digital equipment may 2008. terminology review arrt content specs 2008
TRANSCRIPT
DIGITAL EQUIPMENT
MAY 2008
TERMINOLOGY REVIEW
ARRT CONTENT SPECS
2008
ARRT SPECS - DIGITAL
bull Image Receptorsbull digital image characteristics
ndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix
sizendash image signal (exposure
related)ndash quantum mottlendash SNR (signal to noise ratio)
orndash CNR (contrast to noise ratio)
bull Digital Systemsbull electronic collimationbull grayscale rendition or look-up
table (LUT)bull edge enhancement
ndash noise suppression
bull contrast enhancementbull system malfunctions (eg
ghost image banding erasure dead pixels readout problems printer distortion)
ARRT SPECS - DIGITALbull Image Display
ndash viewing conditions (ie luminanceambient lightingndash spatial resolutionndash contrast resolutiondynamic rangendash DICOM gray scale functionndash window level and width function
bull Image Acquisition and Readoutbull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low contrast)
ARRT SPECS - DIGITAL
bull Recognition of Malfunctions
bull Digital Image Receptor Systems
bull Digital artifacts ndash (grid lines Moireacute effect or aliasing)ndash maintenance (eg detector fog)ndash ( non-uniformity erasure)
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Review of Digital Radiography
and PACS
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
TERMINOLOGY REVIEW
ARRT CONTENT SPECS
2008
ARRT SPECS - DIGITAL
bull Image Receptorsbull digital image characteristics
ndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix
sizendash image signal (exposure
related)ndash quantum mottlendash SNR (signal to noise ratio)
orndash CNR (contrast to noise ratio)
bull Digital Systemsbull electronic collimationbull grayscale rendition or look-up
table (LUT)bull edge enhancement
ndash noise suppression
bull contrast enhancementbull system malfunctions (eg
ghost image banding erasure dead pixels readout problems printer distortion)
ARRT SPECS - DIGITALbull Image Display
ndash viewing conditions (ie luminanceambient lightingndash spatial resolutionndash contrast resolutiondynamic rangendash DICOM gray scale functionndash window level and width function
bull Image Acquisition and Readoutbull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low contrast)
ARRT SPECS - DIGITAL
bull Recognition of Malfunctions
bull Digital Image Receptor Systems
bull Digital artifacts ndash (grid lines Moireacute effect or aliasing)ndash maintenance (eg detector fog)ndash ( non-uniformity erasure)
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Review of Digital Radiography
and PACS
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
ARRT SPECS - DIGITAL
bull Image Receptorsbull digital image characteristics
ndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix
sizendash image signal (exposure
related)ndash quantum mottlendash SNR (signal to noise ratio)
orndash CNR (contrast to noise ratio)
bull Digital Systemsbull electronic collimationbull grayscale rendition or look-up
table (LUT)bull edge enhancement
ndash noise suppression
bull contrast enhancementbull system malfunctions (eg
ghost image banding erasure dead pixels readout problems printer distortion)
ARRT SPECS - DIGITALbull Image Display
ndash viewing conditions (ie luminanceambient lightingndash spatial resolutionndash contrast resolutiondynamic rangendash DICOM gray scale functionndash window level and width function
bull Image Acquisition and Readoutbull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low contrast)
ARRT SPECS - DIGITAL
bull Recognition of Malfunctions
bull Digital Image Receptor Systems
bull Digital artifacts ndash (grid lines Moireacute effect or aliasing)ndash maintenance (eg detector fog)ndash ( non-uniformity erasure)
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Review of Digital Radiography
and PACS
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
ARRT SPECS - DIGITALbull Image Display
ndash viewing conditions (ie luminanceambient lightingndash spatial resolutionndash contrast resolutiondynamic rangendash DICOM gray scale functionndash window level and width function
bull Image Acquisition and Readoutbull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low contrast)
ARRT SPECS - DIGITAL
bull Recognition of Malfunctions
bull Digital Image Receptor Systems
bull Digital artifacts ndash (grid lines Moireacute effect or aliasing)ndash maintenance (eg detector fog)ndash ( non-uniformity erasure)
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Review of Digital Radiography
and PACS
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
ARRT SPECS - DIGITAL
bull Recognition of Malfunctions
bull Digital Image Receptor Systems
bull Digital artifacts ndash (grid lines Moireacute effect or aliasing)ndash maintenance (eg detector fog)ndash ( non-uniformity erasure)
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Review of Digital Radiography
and PACS
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Review of Digital Radiography
and PACS
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Review of Digital Radiography
and PACS
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Key Terms
bull Computed radiographybull DICOM (digital imaging and communications in
medicine)bull Digital imagingbull Digital radiographybull Direct capture DRbull Indirect capture DRbull PACSbull Teleradiology
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Digital
Radiography
DirectCapture
IndirectCapture
Direct-to-DigitalRadiography
(DDR)-Selenium
ComputedRadiography
(CR) - PSL
LaserScanningDigitizers
Direct-to-DigitalRadiographySilicon Scint
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)
bull flat panel detectors ndash (direct and indirect)
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Computed Radiography
bull Uses storage phosphor plates
bull Uses existing equipmentbull Requires special cassettesbull Requires a special cassette
readerbull Uses a computer workstation
and viewing station and a printer
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Computed Radiographybull Storage phosphor plates are similar to
intensifying screensbull Imaging plate stores x-ray energy for an extended timebull Process was first introduced in the
United States by Fuji Medical Systems of Japan in 1983
bull First system used a phosphor storage plate a reader and a laser printer
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Imaging Plate
bull Constructionbull Image recorded on a thin sheet of plastic known
as the imaging platebull Consists of several layers
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Cassette and Imaging Plate
bull Cassette contains a window with a barcode label or barcode sticker on the cassette
bull Label enables technologist to match the image information with the patient-identifying barcode on the exam request
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Using the Laser to Readthe Imaging Plate
bull The light collection optics direct the released phosphor energy to an optical filter and then to the photodetector
bull Although there will be variances between manufacturers the typical throughput is 50 cassettes per hour
bull Some manufacturers claim up to 150 cassettes per hour but based on average hospital department workflow 50 cassettes per hour is much more realistic
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
bull Process up to 101 cassettes an hour
bull bull Handle 16 cassettes at one time
bull up to 8 queued for processing
bull and 8 erased and ready for new
bull imaging studiesbull bull Cassette is ready to
reuse inbull 40 secondsbull bull Review an image in 34
secondsbull at a Kodak DirectView
remotebull operations panelbull bull ldquoDrop-and gordquo
workflow virtually
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
bull Based on proven DirectView CR 850 system design
bull middotProcess up to 62 35 x 43 cm plates an hour
bull middotSmall footprint size of 25 x 29 inch (635 x 736 cm
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Digital Radiography
bull Cassetteless systembull Uses a flat panel detector or
charge-coupled device (CCD) hard-wired to computer
bull Requires new installation of room or retrofit
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Digital Radiography
bull DR is hard-wiredbull DR is cassettelessbull Detectors are permanently enclosed inside a
rigid protective housing bull Thin-film transistor (TFT) detector arrays may
be used in direct- and indirect-conversion detectors
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
bull Two types of digital radiographybull Indirect capture DR
bull Machine absorbs x-rays and converts them to light
bull CCD or thin-film transistor (TFT) converts light to electric signals
bull Computer processes electric signalsbull Images are viewed on computer
monitor
Digital Radiography
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
bull Direct capture DRbull Photoconductor
absorbs x-raysbull TFT collects signalbull Electrical signal is
sent to computer for processing
bull Image is viewed on computer screen
Digital Radiography
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
bull DR used CCD technology developed by the military and then used TFT arrays shortly after
bull CCD and TFT technology developed and continues to develop in parallel
bull No one technology has proved to be better than the other
Digital Radiography
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Flat-Panel Detectors
bull Consist of a photoconductorbull Amorphous selenium
bull Holds a charge on its surface that can then be read out by a TFT
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Direct Conversion
bull X-ray photons are absorbed by the coating material
bull Photons are immediately converted into an electrical signal
bull The DR plate has a radiation-conversion material or scintillator
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Direct Conversion DR Scintillatorbull Typically made of amorphous seleniumbull Absorbs x-rays and converts them to visible
photons bull Converts photons to electrical chargesbull Charges stored in the TFT detectors
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Indirect Conversion
bull Similar to direct detectors in that the TFT technology is also used
bull Two-step processbull X-ray photons are converted to lightbull Light photons are converted to an electrical signal
bull A scintillator converts x-rays into visible light bull Light is then converted into an electrical charge
by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices or CCDs
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Indirect Conversion
bull More than a million pixels can be read and converted to a composite digital image in under a second
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Comparison of Film to CR and DR
bull For conventional x-ray film and computed radiography (CR) a traditional x-ray room with a table and wall Bucky is required
bull For DR a detector replaces the Bucky apparatus in the table and wall stand
bull Conventional and CR efficiency ratings are about the same
bull DR is much more efficient and image is available immediately
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Comparison of Film to CR and DRbull CR
bull A storage phosphor plate is placed inside of CR cassette
bull Most storage phosphor plates are made of a barium fluorohalide
bull When x-rays strike the photosensitive phosphor some light is given off
bull Some of the photon energy is deposited within the phosphor particles to create the latent image
bull The phosphor plate is then fed through the CR reader
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Comparison of CR and DR
bull CR continuedbull Focused laser light is scanned over the plate causing
the electrons to return to their original state emitting light in the process
bull This light is picked up by a photomultiplier tube and converted into an electrical signal
bull The electrical signal is then sent through an analog-to-digital converter to produce a digital image that can then be sent to the technologist review station
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Comparison of CR amp DRbull DR
bull No cassettes are required bull The image acquisition device is built into the table
andor wall stand or is enclosed in a portable device bull Two distinct image acquisition methods are indirect
capture and direct capture bull Indirect capture is similar to CR in that the x-ray
energy stimulates a scintillator which gives off light that is detected and turned into an electrical signal
bull With direct capture the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Amorphous Silicon Detector
bull The light photons are then converted into an electric charge by the photodiode arrays
bull Unlike the selenium-based system used for direct conversion this type of indirect-conversion detector technology requires a two-step process for x-ray detection
bull The scintillator converts the x-ray beams into visible light and light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiodes
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Cesium Iodide Detectors
bull A newer type of amorphous silicon detector uses a cesium iodide scintillator
bull The scintillator is made by growing very thin crystalline needles (5 microm wide) that work as light-directing tubes much like fiber optics
bull This allows greater detection of x-rays and because there is almost no light spread there is much greater resolution
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Cesium Iodide Detectors
bull These needles absorb the x-ray photons and convert their energy into light channeling it to the amorphous silicon photodiode array
bull As the light hits the array the charge on each of the photodiodes decreases in proportion to the light received
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Charge-Coupled Devices
bull The oldest indirect-conversion DR system is based on CCDs
bull X-ray photons interact with a scintillation material such as photostimulable phosphors and this signal is coupled or linked by lenses or fiber optics which act like cameras
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Charge-Coupled Devices
bull These cameras reduce the size of the projected visible light image and transfer the image to one or more small (2 to 4 cm2) CCDs which convert the light into an electrical charge
bull This charge is stored in a sequential pattern and released line by line and sent to an analog-to-digital converter
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Charge-Coupled Devices
bull Even though CCD-based detectors require optical coupling and image size reduction they are widely available and relatively low in cost
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Summary
bull There are two types of cassetteless digital imaging systems direct and indirect
bull Direct sensors are TFT arrays of amorphous silicon coated with amorphous selenium
bull Direct sensors absorb x-ray photons and immediately convert them to an electrical signal
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Summary
bull Indirect-conversion detectors use a scintillator that converts x-rays into visible light which is then converted into an electrical charge
bull CCDs act as miniature cameras that convert light produced by x-ray interaction with photostimulable phosphors into an electrical charge
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Image Display
ndash viewing conditions (ie luminanceambient lighting
ndash DICOM gray scale functionndash window level and width functionndash spatial resolutionndash contrast resolutiondynamic range
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
MONITOR RESOLUTIONDICOM gray scale functionwindow level and width function
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
bull Depending on modalities such as CT CR MRI resolution requirements can range
bull from 13 megapixels to 5 megapixels
bull Generally 3 megapixel and higher class displays are used for softcopy interpretation
bull Where higher accuracy and a subtle reproduction of grayscale are critical in applications such as
bull mammography imaging 5 megapixel resolution is required
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
viewing conditions luminanceambient lighting
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
DICOM gray scale functionwindow level and width function
bull A photometer to a monitor screen in a check of the monitors conformance with the DICOM Grayscale Standard Display Function
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
DICOM gray scale functionwindow level and width function
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Grayscale or color monitors
Digital Systemselectronic collimationgrayscale rendition or look-up table (LUT)edge enhancement
noise suppressioncontrast enhancement
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Detective Quantum Efficiency
bull How efficiently a system converts the x-ray input signal into a useful output image is known as detective quantum efficiency or DQE
bull DQE is a measurement of the percentage of x-rays that are absorbed when they hit the detector
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Detective Quantum Efficiency
bull In other words CR records all of the phosphor output Systems with higher quantum efficiency can produce higher-quality images at a lower dose
bull Indirect and direct DR capture technology has increased DQE over CR
bull However DR direct capture technology because it does not have the light conversion step and consequently no light spread increases DQE the most
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Image Display
bull spatial resolutioncontrast resolutiondynamic range
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Spatial Resolution
bull Spatial resolution refers to the amount of detail present in any image
bull Phosphor layer thickness and pixel size determines resolution in CR
bull The thinner the phosphor layer is the higher resolution
bull Filmscreen radiography resolution at its best is limited to 10 line pairs per millimeter (lpmm)
bull CR resolution is 255 lpmm to 5 lpmm resulting in less detail
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Spatial Resolution
bull CR dynamic range or the number of recorded densities is much higher and lack of detail is difficult to discern
bull More tissue densities on the digital radiograph are seen giving the appearance of more detail
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
SPATIAL RESOLUTION
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Spatial Resolution determined by
1048697 Pixel sizebull CR- sampling frequencybull DR ndash DEL sizebull 1048697 There are relationships betweenbull Pixel sizebull Receptor sizebull Matrix sizebull 1048697 pixel size = larger matrixbull 1048697 receptor size = larger matrixbull Spatial resolution is not related the amount of exposure
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Spatial Resolutionbull knee radiograph typically
does not show soft tissue structures
bull A digital image shows not only the soft tissue but also the edge of the skin This is due to the wider dynamic recording range and does not mean that there is additional detail
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Spatial Resolution
bull Depending on the physical characteristics of the detector spatial resolution can vary a great deal
bull Spatial resolution of amorphous selenium for direct detectors and cesium iodide for indirect detectors is higher than CR detectors but lower than filmscreen radiography
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Spatial Resolution
bull Excessive image processing in an effort to alter image sharpness can lead to excessive noise
bull Digital images can be processed to alter apparent image sharpness however excessive processing can lead to an increase in perceived noise
bull The best resolution is achieved by using the appropriate technical factors and materials
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Speed
bull In conventional radiography speed is determined by the size and layers of crystals in the film and screen
bull In CR speed is not exactly the same because there is no intensifying screen or film
bull The phosphors emit light according to the width and intensity of the laser beam as it scans the plate resulting in a relative speed that is roughly equivalent to a 200-speed filmscreen system
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Speed
bull CR system speeds are a reflection of the amount of photostimulable luminescence given off by the imaging plate while being scanned by the laser
bull For example Fuji Medical Systems reports that a 1-mR exposure at 80 kVp and a source-to-image distance of 72 inches will result in a luminescence value of 200 hence the speed number
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Speed
bull In CR most cassettes have the same speed however there are special extremity or chest cassettes that produce greater resolution
bull These are typically 100 relative speedbull Great care must be taken when converting to a
CR system from a filmscreen system to adjust technical factors to reflect the new speed
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Latitude or Dynamic Range
bull Conventional radiographybull Based on the characteristic response of the film
which is nonlinear bull Radiographic contrast is primarily controlled by
kilovoltage peakbull Optical density on film is primarily controlled by
milliampere-second setting
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
CR Cassettes
bull Because so many more densities are recorded in CR (wide dynamic range) images appear more detailed
bull Because energy stored in the imaging plate is lost over time imaging plates should be read as quickly as possible to avoid image information loss
bull Imaging plates are erased by exposing them to bright light such as fluorescent light
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Latitudeor Dynamic Range
bull CR and DRbull Contain a detector that can respond in a linear
mannerbull Exposure latitude is wide allowing the single detector
to be sensitive to a wide range of exposuresbull Kilovoltage peak still influences subject contrast but
radiographic contrast is primarily controlled by an image processing look-up table LUT
bull Milliampere-second setting has more control over image noise whereas density is controlled by image-processing algorithms
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Density
bull 25 TO -25
bull The straight line of the HampD curve
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Optical Densitybull A numerical value indicating the degree of blackening on
the film (average OD seen on a radiograph = 12 Range is 021 ndash
25)
of photons coming through film = OD of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Why do digital systems havesignificantly greater latitude
bull Linear response give the imaging plates greater latitude
bull Area receving little radiation can be enhanced by the computer
bull Higer densities can be separated and brought down to the visibile density ranges
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
NoteIt is important to note that just because abull digital imaging system has the capacity tobull produce an image from gross underexposurebull or gross overexposure it does not equate tobull greater exposure latitude bull The reason the system is capable of producing
an image when significant exposure errors occur is through a process called automatic rescaling
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
bull In a digital system underexposure of
bull 50 or greater will result in a mottled
bull image
bull 1048697 In a digital system overexposure
bull greater than 200 of the ideal will result
bull in loss of image contrast
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Look-Up Table
bull The look-up table (LUT) is a reference histogram
bull LUT is used as a cross-reference to transform the raw information
bull LUT is used to correct valuesbull LUT has a mapping function
bull All pixels are changed to a new gray value
bull Image will have appropriate appearance in brightness and contrast
bull LUT is provided for every anatomic part
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Look-Up Tablebull LUT can be graphed as follows
bull Plotting the original values ranging from 0 to 255 on the horizontal axis
bull Plotting new values also ranging from 0 to 255 on the vertical axis
bull Contrast can be increased or decreased by changing the slope of this graph
bull Brightness (density) can be increased or decreased by moving the line up or down the y-axis
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Histogram Analysis
bull It is important to choose the correct anatomic region on the menu before exposing the patient
bull Raw data used to form the histogram are compared with a ldquonormalrdquo histogram of the same body part by the computer
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Matrix size is determined by
bull 1048697 Receptor size (Field of View FOV)
bull 1048697 Pixel size
bull CR - Sampling frequency
bull DR - DEL size (Dector ELement)
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
DIGITAL MATRIX SIZE
bull The number of rows and columns of
bull pixels in the image representation
bull 7 X 7
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Digital - GrayscaleBit depth
1048697Number of gray shades available for display
bull 8 bit 256
bull 10 bit 1024
bull 12 bit 4096
bull 14 bit 16384
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Digitizing the Signal
bull So how bright a pixel is determines where it will be located in the matrix in conjunction with the amount of gray level or bit depth
bull Some CR systems have bit depths of 10 or 12 resulting in more shades of gray
bull Each pixel can have a gray level between 0 (20) and 4096 (212) The gray level will be a factor in determining the quality of the image
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Summary
bull Pixel and matrix size are important in determining the amount of resolution and the size of the image to be stored in the PACS system In TFT technology pixel and matrix size are determined by the amount of area available to ldquofillrdquo with photons
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
ARRT SPECS - DIGITAL
bull PACSbull HIS (hospital information system) - work
listbull RIS (radiology information system)bull DICOMbull Workflow (inappropriate documentation
lost images mismatched images corrupt data)
bull windowing and leveling
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Picture Archival andCommunication Systems
bull Networked group of computers servers and archives to store digital images
bull Can accept any image that is in DICOM format
bull Serves as the file room reading room duplicator and courier
bull Provides image access to multiple users at the same time on-demand images electronic annotations of images and specialty image processing
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
PACS
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
PACS Uses
bull Made up of different componentsbull Reading stationsbull Physician review stationsbull Web accessbull Technologist quality control stationsbull Administrative stationsbull Archive systemsbull Multiple interfaces to other hospital and radiology
systems
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
DICOM
bull stands for digital imaging and communications in medicine and it is a universally accepted standard for exchanging medical images between networked medical devices
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
HIS RIS
bull The HIS holds the patientrsquos full medical information from hospital billing to the inpatient ordering system
bull The RIS holds all radiology-specific patient data from the patient scheduling information to the radiologistrsquos dictated and transcribed report
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
HIS ndash RIS INTERFACE
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Image Acquisition and Readout
bull PSP (photo-stimulable phosphor)bull flat panel detectors
ndash (direct and indirect)
bull Noisebull Acceptable Range of Exposurebull Exposure Indicator Determinationbull Gross Exposure Errorbull Image Degradation (mottle light or dark low
contrast)
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Indicators
bull The amount of light given off by the imaging plate is a result of the radiation exposure that the plate has received
bull The light is converted into a signal that is used to calculate the exposure indicator number which is a different number from one vendor to another
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Indicators
bull The base exposure indicator number for all systems designates the middle of the detector operating range
bull For Fuji Phillips and Konica systems the exposure indicator is known as the S or sensitivity number
bull The S number is the amount of luminescence emitted at 1 mR at 80 kVp and it has a value of 200
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Indicators
bull The higher the S number with these systems the lower the exposure
bull For example an S number of 400 is half the exposure of an S number of 200 and an S number of 100 is twice the exposure of an S number of 200
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Indicators
bull The numbers have an inverse relationship to the amount of exposure so that each change of 200 results in a change in exposure by a factor of 2
bull Kodak uses exposure index or EI as the exposure indicator
bull A 1 mR exposure at 80 kVp combined with aluminumcopper filtration yields an EI number of 2000
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Indicators
bull An EI number plus 300 (EI + 300) is equal to a doubling of exposure and an EI number of minus 300 (EI minus 300) is equal to a halving of exposure
bull The numbers for the Kodak system have a direct relationship to the amount of exposure so that each change of 300 results in change in exposure by a factor of 2
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Indicators
bull This is based on logarithms only instead of using 03 (as is used in conventional radiographic characteristic curves) as a change by a factor of 2 the larger number 300 is used
bull This is also a direct relationship the higher the EI the higher the exposure
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Exposure Indicators
bull The term for exposure indicator in an Agfa system is the lgM or logarithm of the median exposure
bull An exposure of 20 microGy at 75 kVp with copper filtration yields an lgM number of 26
bull Each step of 03 above or below 26 equals an exposure factor of 2
bull An lgM of 29 equals twice the exposure of 26 lgM and an lgM of 23 equals an exposure half that of 26
bull The relationship between exposure and lgM is direct
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Image Receptors
digital image characteristicsndash spatial resolutionndash sampling frequencyndash DEL (detector element size)ndash receptor size and matrix sizendash image signal (exposure related)ndash quantum mottlendash SNR (signal to noise ratio) orndash CNR (contrast to noise ratio)
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Stiching an image
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Portrait vs landscape mode
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Edge enhancement amp post processing
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Enhanced Visualization Image Processing
bull Kodakbull Takes image diagnostic quality to a new levelbull Increases latitude while preserving contrastbull Process decreases windowing and levelingbull Virtually eliminates detail loss in dense tissues
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Grid Selectionbull Digital images are
displayed in tiny rows of picture elements or pixels
bull Grid lines that are projected on the imaging plate when using a stationary grid can interfere with the image resulting in a wavy artifact known as a moireacute pattern
bull This pattern occurs because the grid lines and the scanning laser are not parallel
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Collimation
bull Although the use of a grid decreases the amount of scatter that exits the patient from affecting latent image formation properly used collimation reduces the area of irradiation and reduces the volume of tissue in which scatter can be created
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Collimationbull This results in increased contrast because of the
reduction of scatter as fog and reduces the amount of grid cleanup necessary for increased resolution
bull Through postexposure image manipulation known as shuttering a black background can be added around the original collimation edges virtually eliminating the distracting white or clear areas
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Collimation
bull However this technique is not a replacement for proper preexposure collimation
bull Shuttering is an image aesthetic only and does not change the amount or angles of scatter created
bull There is no substitute for appropriate collimation for collimation reduces patient dose
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Automatic Data Recognition
bull Collimation is automatically recognized and a complete histogram analysis occurs
bull Good collimation practices are critical because overcollimation or undercollimation leads to data recognition errors that affect the histogram
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Mis registration ndash needs reprocessing
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Common CR Image Acquisition Errors
bull As with film screen artifacts can detract and degrade imagesndash Imaging plate artifacts
bull Plate reader artifactsbull Image processing artifactsbull Printer artifactsbull Operator errors
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Imaging Plate Artifactsbull As the imaging plate ages it becomes prone to cracks
from the action of removing and replacing the imaging plate within the reader
bull Cracks in the imaging plate appear as areas of lucency on the image
bull The imaging plate must be replaced when cracks occur in clinically useful areas
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Imaging Plate Artifactsbull Adhesive tape used to secure lead markers to the
cassette can leave residue on the imaging plate bull If static exists because of low humidity hair can
cling to the imaging plate
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Imaging Plate Artifactsbull Backscatter created by x-ray photons transmitted through the back of the cassette
can cause dark line artifacts
bull Areas of the lead coating of the cassette that are worn or cracked allow scatter to image these weak areas Proper collimation and regular cassette inspection helps to eliminate this problem
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Plate Reader Artifactsbull The intermittent appearance of extraneous line patterns can be
caused by problems in the electronics of the plate reader
bull Reader electronics may have to be replaced to remedy this problem
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Plate Reader Artifactsbull Incorrect erasure settings result in a residual image
left in the imaging plate before the next exposure bull Results vary depending on how much residual image
is left and where it is located bull Orientation of a grid so that the grid lines are parallel
to the laser scan lines of the plate reader results in the moireacute pattern error Grids should be high frequency and the grid lines should run perpendicular to the laser scan lines of the plate reader
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Operator Errorsbull Insufficient collimation results in unattenuated radiation
striking the imaging plate
bull The resulting histogram is changed so that it is outside the normal exposure indicator range for the body part selected
bull Using the smallest imaging plate possible and proper collimation especially on small or thin patients eliminates this error
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
Operator Errors
bull If the cassette is exposed with the back of a cassette toward the source the result is an image with a white grid-type pattern and white areas that correspond to the hinges
bull Care should be taken to expose only the tube side of the cassette
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-
- DIGITAL EQUIPMENT
- TERMINOLOGY REVIEW
- ARRT SPECS - DIGITAL
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Review of Digital Radiography and PACS
- Key Terms
- Slide 10
- Image Acquisition and Readout
- Computed Radiography
- Slide 13
- Imaging Plate
- Cassette and Imaging Plate
- Using the Laser to Read the Imaging Plate
- Slide 17
- Slide 18
- Digital Radiography
- Digital Radiography
- Slide 21
- Slide 22
- Slide 23
- Flat-Panel Detectors
- Direct Conversion
- Direct Conversion DR Scintillator
- Indirect Conversion
- Slide 28
- Comparison of Film to CR and DR
- Slide 30
- Comparison of CR and DR
- Comparison of CR amp DR
- Amorphous Silicon Detector
- Cesium Iodide Detectors
- Slide 35
- Charge-Coupled Devices
- Slide 37
- Slide 38
- Summary
- Slide 40
- Image Display
- MONITOR RESOLUTION
- Slide 43
- viewing conditions luminanceambient lighting
- DICOM gray scale function window level and width function
- Slide 46
- Slide 47
- Slide 48
- Slide 49
- Slide 50
- Slide 51
- Grayscale or color monitors
- Detective Quantum Efficiency
- Slide 54
- Slide 55
- Spatial Resolution
- Slide 57
- SPATIAL RESOLUTION
- Spatial Resolution determined by
- Slide 60
- Slide 61
- Slide 62
- Slide 63
- Speed
- Slide 65
- Slide 66
- Exposure Latitude or Dynamic Range
- CR Cassettes
- Exposure Latitude or Dynamic Range
- Density
- Optical Density
- Slide 72
- Slide 73
- Slide 74
- Why do digital systems have significantly greater latitude
- Note
- Slide 77
- Slide 78
- Look-Up Table
- Slide 80
- Histogram Analysis
- Image Receptors
- Slide 83
- DIGITAL MATRIX SIZE
- Slide 85
- Slide 86
- Digital - Grayscale Bit depth 1048737
- Slide 88
- Digitizing the Signal
- Slide 90
- Slide 91
- Slide 92
- Picture Archival and Communication Systems
- PACS
- PACS Uses
- DICOM
- HIS RIS
- HIS ndash RIS INTERFACE
- Slide 99
- Exposure Indicators
- Slide 101
- Slide 102
- Slide 103
- Slide 104
- Slide 105
- Slide 106
- Slide 107
- Stiching an image
- Portrait vs landscape mode
- Edge enhancement amp post processing
- Enhanced Visualization Image Processing
- Grid Selection
- Collimation
- Slide 114
- Slide 115
- Automatic Data Recognition
- Mis registration ndash needs reprocessing
- Common CR Image Acquisition Errors
- Imaging Plate Artifacts
- Slide 120
- Slide 121
- Plate Reader Artifacts
- Slide 123
- Operator Errors
- Slide 125
- Slide 126
-