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Digital Radiography

Fall 2012

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filmless’ radiology departments

Diagnostic radiographers

have traded their film and chemistry

for a computer mouse

and monitor

advance for Rad Sci Prof, 8/9/99

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What Is Digital Imaging?

Digital imaging is the acquisition of images to a computer rather than directly to film.

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New Technology Has impacted everyone:

1. Practicing radiologic technologist

2. Educators

3. Administrators

4. Students in the radiologic sciences.

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Computed Radiography

Fundamentals of

Computerized Radiography

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Radiology 1895 Radiology 2001

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CR SYSTEM COMPONENTS

1. CASSETTES (phosphor plates)

2. ID STATION

3. IMAGE PREVIEW (QC) STATION

4. DIGITIZER

5. VIEWING STATION

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History of CR

INDUSTRY • Theory of “filmless radiography” first

introduced in 1970

• 1981 Fugi introduced special cassettes with PSP plates (replaces film)

• Technology could not support system

• First clinical use in Japan - 1983

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Predictions 1980 – Bell Labs believed that Unix would

be the worlds dominant operating system

1982 – Bill Gates thought 640K of main memory would suffice for workplace operating systems ( This presentation is 80,000 kb)

1984 – IBM predicted that personal computers would not amount to anything

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History of CR By 1998 – over 5,000 CR systems in use

nationwide

1998 – Local area hospitals begin to incorporate CR systems in their departments

(Riverside Co. Hosp builds new hospital in Moreno Valley) – completely CR system – 1st generation equipment

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TERMINOLOGY

1. F/S - Film/Screen (currently used method)

2. CR - Computed Radiography

3. DR - Digital Radiography

4. DDR - Direct to Digital Radiography

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IMAGE CREATION SAME RADIOGRAPHY EQUIPMENT

USED

THE DIFFERENCE IS HOW IT IS 1. CAPTURED2. STORED3. VIEWED4. And POST -PROCESSED

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Conventional vs. Digital Imaging

Conventional X-ray imaging systems Produce an analog image

(radiographs, & fluoroscopy). Using x-ray tube with films &

cassettes

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Conventional vs. Digital Imaging

Digital radiography systems require that the electronic signal be converted to a digital signal –

Using x-ray tube – CR cassettes with phosphor plate (PSP) DR systems with transistors (TFT)

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COMPUTED RADIOGRAPHY & DIRECT RADIOGRAPHY

& FILM SCREENIMAGE CAPTURE

FS - Film inside of cassette

CR – Photostimuable Phosphor Plate (PSP)

DR(DDR) - Thin Film Transitor (TFT)

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Cassette with film CR with PSP

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Directed Digital Radiography

(DDR)

Directed digital radiography, a term used to describe total electronic imaging capturing.

Eliminates the need for an

image plate altogether.

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Amorphous Selenium detector technology for DR Direct Radiography

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IMAGE CAPTURE

1. CR PSP – photostimulable phosphor plate Replaces film in the cassette

2. DR – No cassette- Photons captured directly onto TFT Sent directly to a monitor

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CR vs. FS CR PSP in cassette Digital image Scanned & read- CR

reader

COMPUTER Image stored on

computer Viewed on a

Monitor Hard copy (film)

can be made with laser printer

FILM Film in cassette loaded in a

darkroom Processed in a

processor

FILM Hard copy image –

stores the image Viewboxes – view

the images

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CR BASICS• Eliminates the need for film as a

recording, storage & viewing medium.

• PSP Plate – receiver

• Archive Manager – storage

• Monitor - Viewing

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General Overview CR

PSP cassette exposed by conventional X-ray equipment.

Latent image generated as a matrix of trapped electrons in the plate.

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CR – PSP plate

1. Photostimulable phosphor (PSP) plate

2. Captures photons

3. Stored in traps on plate (latent image)

4. PLATE scanned in CR READER

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CR – PSP plate

1. Stimulated by a RED LIGHT

2. Energy is RELEASED in a form of BLUE light

3. LIGHT captured by photomultiplier tube (PMT)

4. Changed to a digital signal

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How CR works

1. Blue released light is captured by a PMT (photo multiplier tube)

2. This light is sent as a digital signal to the computer

3. The intensity (brightness) of the light – correlates to the density on the image

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PMT

Beam deflector

LaserSource

Light channeling guide

Plate translation: Sub-scan direction

Laser beam: Scan direction

Output Signal

Reference detec tor

Beam splitter

Cylindrical m irrorf-thetalens

Amplifier

ADC

To imageprocessor

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X-rayX-raysystemsystem

PatientPatient

PSPPSPdetector detector

ComputedComputedRadiographRadiograph

1. X-ray Exposure1. X-ray Exposure

ImageImageReaderReader

2.2.

ImageImageScalingScaling

3.3.

ImageImageRecorderRecorder

4.4.

une xposedune xposed

exposedexposed

5.5.

re-usablere-usablephosphorphosphor

plateplate

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CR “PROCESSORS”

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Densities of the IMAGE

1. The light is proportional to amount of light received

2. Digital values are then equivalent (not exactly the same) to a value of optical density (OD) from a film, at that location of the image

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ERASING PLATE

1. After image is recorded

2. Plate is erased with high intensity white light

3. Cassettes are reused

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CR VS. DR (slide 41)

CR -Indirect capture where the image is first captured on plate and stored = then converted to digital signal

DDR -Direct capture where the image is acquired immediately as a matrix of pixels – sent to a monitor

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Digital

Radiography

DirectCapture

IndirectCapture

Direct-to-DigitalRadiography

(DDR)

ComputedRadiography

(CR)

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DIRECT RADIOGRAPHY Uses a transistor receiver (like bucky)

Captures and converts x-ray energy directly into digital signal

Images seen immediately on monitor

Sent to PACS/ printer/ other workstations FOR VIEWING

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CR vs DRCR Imaging plate

Processed in a Digital Reader

Signal sent to computer

Viewed on a monitor

DR Transistor receiver

(like bucky)

Directly into digital signal

Seen immediately on monitor

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ADVANTAGE OF CR/DR Can optimize image quality

Can manipulate digital data

Improves visualization of anatomy and pathology

AFTER EXPOSURE TO PATIENT

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ADVANTAGE OF CR/DR

Changes made to image after the exposure

Can eliminate the need to repeat the exposure

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ADVANTAGE OF CR/DR vs FS1. Rapid storage

2. Retrieval of images NO LOST FILMS!

3. PAC (storage management)

4. Teleradiology - long distance transmission of image information

5. Economic advantage - at least in the long run?

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CR/DR VS FILM/SCREEN

1. FILM- these can not be modified once processed

2. If copied – lose quality

3. DR/CR – print from file – no loss of quality

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“No fault” TECHNIQUES

F/S: RT must choose technical factors (mAs & kvp) to optimally visualize anatomic

detail

CR: the selection of processing algorithms and anatomical regions controls how the acquired latent image is presented for display

HOW THE IMAGE LOOKS CAN BE ALTERED BY THE COMPUTER – EVEN WHEN “BAD” TECHNIQUES ARE SET

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DR

1. Initial expense high

2. Very low dose to pt –

3. Image quality of 100s using a 400s technique

4. Therefore ¼ the dose needed to make the image

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Storage /ArchivingFILM/SCREEN

1. Films: bulky

2. Deteriorates over time

3. Requires large storage & expense

4. Environmental concerns

CR & DR

1. 8000 images stored on CD-R

2. Jukebox CD storage

3. No deterioration of images

4. Easy access

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Transmission of Images

1. PACS - Picture Archiving & Communications System

2. DICOM - Digital Images & Communication in Medicine

3. TELERADIOGRAPHY -Remote Transmission of Images

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Benefits of Computer (web)-based Viewing Systems

1. Hardcopy studies are no longer misplaced or lost- eliminates films

2. Multiple physicians may access same patient films

3. Patients do not have to wait in Radiology for films once study is completed

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“Film-less” components

1. CR or DR2. CD-ROM or similar

output3. Email capability4. Digitizing capability or

service

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PACS

Internet VPN

Digital Images Archive

Databaseand Workflow Engine

Workstations

Remote Workstations

Remote Facilities

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Histogram Analysis

1. A histogram is a plot of gray scale value

2. vs. the frequency of occurrence

3. (# pixels) of the gray value in the image

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HISTOGRAM – a bar graph depicting the density distribution (in numerical values) of the imaging plate

ALGORITHM – a set of mathematical values used to solve a problem or find an average

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0 200 400 600 800 1,0000

2,000

4,000

6,000

8,000

10,000

12,000

Digital number

Fre

qu

ency

High attenuation(e.g., mediastinum)

Low attenuation(e.g., lungs)

Histogram

Adapted from AAPM TG10

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Statistical plots of the

frequency of occurrence of

each pixel's value

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Basics of Digital Images

Digital images are a (matrix) of pixel (picture element) values

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The algorithm attempts to distinguish among the parts of the histogram which represent the range of densities from bone to soft tissue

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Histograms set for specific exams (body parts)

Should produce digital images that are consistent (regardless of kVp or mAs used)

Correct Algorithm (body part) must be selected prior to processing imaging plate

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Methods to Digitize an Image

1. Film Digitizer - Teleradiography system (PACS, DICOM)

2. Video Camera (vidicon or plumbicon)

3. Computed Radiography

4. Direct Radiography

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FILM DIGITIZER

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Analog vs Digital (slide 73)1. Analog - one value

blends into another

1. like a thermometer

2. Digital - distinct separation

1. 98.6 2. exact

0

20

40

60

80

100

1st

Qtr

3rd

Qtr

East

West

North

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ANALOG TO DIGITAL IMAGE

1. Conversion of conventional analog films

2. To digital format for PACs and teleradiology applications

3. With scanning laser digitizers

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CONTRAST & DENSITY1. Most digital systems are capable of

1024 shades of gray – but the human eye can see only about 30

shades of gray

2. The Optical Density and Contrast can be adjusted after the exposure by the Radiographer.

3. This is POST - PROCESSING

73High displayed contrast – narrow window width

74Low displayed contrast (stretched) – wide window width

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Basics of Digital Images1. Pixel values can be any bit depth

(values from 0 to 1023)

2. Image contrast can be manipulated to stretched or contracted to alter the displayed contrast.

3. Typically use “window width” and “window level” to alter displayed contrast

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55 15 30

100 200 500

80 KVP

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Then the COMPUTER corrects any exposure errors

Therefore almost ANY technique can be used on the patient –

The computer will fix it

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DOSE IMPLICATIONS

1. More exposure to the patient2. Techniques established

3. Higher kVp = Less mAs 4. Less patient dose

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80 kvp 200mas

10 mas 80 kvp

Note

Quantum Mottle

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Dose Implications

1. Images nearly always look better at higher exposures.

2. Huge dynamic range means nearly impossible to overexpose.

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POST PROCESSING

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TECHNIQUE CONISDERATIONS

1. KVP Dependant

2. Now COMPUTER controls CONTRAST

3. Higher kVp to stimulate electron traps

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standard image edge sharpening

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NO GRID HAND ALGO

REPROCESSED

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QC – Reader (replaces Darkroom & Processor & Chemicals

Diagnostic Viewer(replaces film, storage & viewboxes)

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REPEAT IMAGES

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EMERGING PROBLEMS

1. Better – not necessarily faster

2. Learning curve for technologists and physicians

3. Student applications and issues

4. Pitfalls of CR

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COLLIMATION CRITICAL

1. As the computer reads the density value of each pixel- it is averaged into the total

2. Close collimation= Better contrast

3. Bad collimation= more grays and less detail

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1. Digital imaging is not the end all, cure all for imaging problems

2. It is still technologist dependent

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To Produce Quality ImagesFor Conventional Projection

or CR Radiography: The same rules, theories, and laws still

apply and can not be overlooked FFD/OFD (SID/SOD) Inverse Square Law Beam Alignment Tube-Part-Film Alignment Collimation Grids

Exposure Factors: KVP, MaS

Patient Positioning

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NEW IMAGE• Towel that was used to help in positioning a child

• CR is MORE sensitive to

• ARTIFACTS

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CR image – NEW IMAGE

Line caused from dirt collected in a CR Reader

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High resolution with digital imaging