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Image Receptors

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Digital

Radiography

DirectCapture

IndirectCapture

Direct-to-DigitalRadiography

(DDR)

ComputedRadiography

(CR)

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Computed Radiography

Similar to F/S Uses cassettes as imaging plate (IP)

Imaging plate is termed PSP

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History of CR

INDUSTRY • Theory of “filmless radiography” first

introduced in 1970

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

• Technology could not support system

• First clinical use in Japan - 1983 5

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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Uses the same generalequipment as F/S

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How is it different from F/S?

How the image is captured How the image is stored How the image is viewed How the image is processed after

taken

Computed Radiography

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Review of F/S image production:

Primary beam Exit radiation Hits phosphors of intensifying screens, lights

helps form image-latent image Some photons hit film directly-latent image Film is processed to develop manifest image Film stored, duplicated to be seen by others

Computed Radiography

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Computed Radiography Image Production:

Primary beam-same as film Exit radiation-same as film Interacts with CR cassette image plate- latent image latent image -

similar to film CR cassette is place in CR reader, laser translates

image to analog signal-different Analog signal converted to digital signal Image can be viewed on computer monitor-manifest manifest

imageimage Image can be post-processed-not possible with F/S Image is stored in computer system (PACS) Image can be viewed by anyone with access to system Image can be printed on film with a laser printer

Computed Radiography

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Cassette with film CR with PSP

Film Cassette

CR cassette with PSP

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Computed Radiography

Responds to radiation by trapping energy in the locations where x-rays strike, creating the latent image

PSP run scanned by a CR reader, converted to analog image, then to digital image, then image viewed on monitor.

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CR Reader- scans the PSP plate

using a RED laser light, releases trapped electrons which then emit BLUE light which is converted to analog image.

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Computed Radiography

Uses red light to scan

Detects the Blue light emitted

Exit radiation exposes CR cassette

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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 15

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

Computed Radiography

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CR Phosphor PlatesCR Phosphor Plates

ABSORPTION EMISSION

X-RAY

LIGHT

LASER STIMULATION

ELECTRONTRAP

ELECTRONTRAP

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How CR works

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

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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ERASING PLATE

1. After image is recorded

2. Plate is erased with high intensity white light

3. Cassettes are reused

Remember RED, WHITEWHITE AND BLUE…..but really it goes Red, Blue White…

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Digital

Radiography

DirectCapture

IndirectCapture

Direct-to-DigitalRadiography

(DDR)

ComputedRadiography

(CR)

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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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Cassette-less imaging Uses TFT-Thin Film Transistor No film, so no developing, No PSP, so CR reader needed Immediate image viewing Post Processing capabilities Multiple viewing stations

Direct Digital Radiography

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Amorphous Selenium detector technology for DR Direct Radiography

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Direct Digital Radiography

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Be able to compare all the different Be able to compare all the different imaging systems. Compare the imaging systems. Compare the

advantages, disadvantages of each advantages, disadvantages of each system. system.

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FS - Film inside of cassetteFS - Film inside of cassette

CR – Photostimulable Phosphor Plate (PSP)CR – Photostimulable Phosphor Plate (PSP)

DR(DDR) - Thin Film Transistor (TFT)DR(DDR) - Thin Film Transistor (TFT)

Don’t forget about Direct Exposure !!Don’t forget about Direct Exposure !!

FS vs. CR

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 28

CR vs DR

CR 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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COMPUTED RADIOGRAPHY & DIRECT RADIOGRAPHY& FILM SCREEN IMAGE CAPTURE

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Image Resolution (how sharply is the image seen)

CR 4000 x 4000

Image only as good a monitor*

More pixels = more memory needed to store

CR 2 -5 lp/mm RAD 10 lp/mm DR ?

IMAGE APPEARS SHARPER BECAUSE CONTRAST CAN BE ADJUSTED BY THE COMPUTER –

(DIFFERENCES IN DENSITY)

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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 32

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 34

Storage /Archiving

FILM/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 access35

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ADVANTAGE OF CR/DR vs FS

1. Rapid storage

2. Retrieval of images NO LOST FILMS!

3. PACS- DICOM (storage management)

4. Teleradiology - long distance transmission of image information

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

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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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Basics of Digital Images

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

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Analog vs Digital1. Analog - one value

blends into another1. 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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CONTRAST & DENSITY

1. 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 - PROCESSING41

High displayed contrast – narrow window width42

Low displayed contrast (stretched) – wide window width43

Basics of Digital Images

1. 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 44

Danger of Digital

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-F/S techniques

3. Higher kVp = Less mAs 4. Less patient dose5. Goes Contrary to what good techs have been

taught

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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 CONSIDERATIONS

1.kVp Dependent

2. Now COMPUTER controls CONTRAST

3. Higher kVp to stimulate electron traps

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CR – Reader (replaces Darkroom & Processor & Chemicals

Diagnostic Viewer(replaces film, storage & viewboxes)

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EMERGING PROBLEMS

1. Better – not necessarily faster

2. Learning curve for technologists and physicians-increase repeat rate?

3. Student applications and issues

4. Pitfalls of CR52

Learning Curve

1. Positioning and proper collimation are critical to good imaging outcomes

2. Just like Phototiming, it can magnify your mistakes

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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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To Produce Quality Images

For Conventional Radiography or CR Radiography:

The same rules, theories, and laws still apply and can not be overlooked SID, Inverse Square Law, Beam Alignment ,Tube-Part-Film Alignment, Collimation, Grid, Exposure Factors: kVp, mAs

Patient Positioning

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Quality Images

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Towel that was

used to help in positioning a child

CR/DR is MORE sensitive to ARTIFACTS

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