This document discusses computed radiography (CR), which is an indirect digital radiography technique. In CR, x-rays create a latent image on a photostimulable phosphor plate, which is then read with a laser and converted to a digital image. This allows for digital processing and archiving of images. While CR images have improved quality over film, attention must be paid to potential increases in patient dose from retakes or higher than needed image quality. Digital detectors also have a wider dynamic range than film, allowing "good" images even if dose is excessive.

1. Mrs. BHUVANESHWARI.P
M.Sc. MEDICAL PHYSICS
LECTURER
GANGA COLLEGE OF NURSING
COIMBATORE

2. COMPUTED
RADIOGRAPHY

3. RADIOGRAPHY
It is an art and science of recording
images produced by X-rays on film
 Film act as
Image
receptor
Display
medium
Permanent
record

4. Radiography
Patient
FSR
Film Screen
Radiography
Imaging Plate
CR - 2 Step
Digital Detector
DR – 1 Step
Transmitted X-rays

5. Equipment for digital
radiography

6. Equipment for digital
radiography
 CR involves an intermediate step in which the
image is stored as a latent image, in a cassette-
like device, before it is converted to
electronic/digital form, using laser stimulation
 In DR, the image is created immediately in
electronic/digital form, in the image receptor
 Images from both systems can be displayed on
suitable high-resolution monitors or printed out
on film

7. Screen-film vs digital radiography
 Digital images can be numerically modified
(not possible in screen-film radiography)
 Digital images can be easily transmitted
through networks and archived
 Attention should be paid to the potential
increase of patient dose due to a tendency to:
– produce more images than needed
– produce higher image quality not
necessarily required for the clinical purpose.

8. Screen-film vs digital radiography
Conventional films directly show the
selection of wrong exposure
parameters: images are too white or
too black.
Digital technology always provides user
with a “good image”, since its
dynamic range and tone-scaling
compensates for wrong settings even
if the dose is higher than necessary.

9. What is “dynamic range”?
 Wide dose range to the detector
allows “good” tone scale to be
obtained at different dose levels.
 Digital detectors have a dynamic
range of 104 (from 1 to 10,000),
while a screen-film system has
approximately 101.5 (from 1 to 30).

10. Screen-film vs digital
radiography
Digital detector

11. Screen-Fim vs Digital
Dadiography
 The key advantage of CR and DR is
greatly improved contrast resolution,
accompanied by almost infinite
possibilities with digital processing .

12. Digital radiography
 In general, digital imaging has potential for dose
reduction while improving image quality and
diagnostic accuracy
 But only with much attention to:
– staff training
– continuous monitoring of parameters and
practices
 The key issue is that, because of image
processing, the tone scale will continue to look
good even if the dose increases

13. Digital Radiography
 Indirect digital
Radiography
 Film Digitization
 Computed Radiography
 Direct digital
Radiography
– CCD Cameras
– CMOS Cameras
– Thin Film Transistor
(TFT) Flat Panel Arrays
Depending on mode of acquisition and
capture of the x-ray image with/without
user intervention.

15. 15

16. Cassettes

17. IMAGING PLATES
Light reflective Layer
Support
Light shielding layer (Carbon
particle in binder)
Bracode label (Serial no. for
identification)
Backing layer.

18. IMAGING PLATES
Photostimulable Storage Phosphor plates.
Standard grade imaging plate has 210 um thick
phosphor layer with a reflective backing on a
polyester base
Thin protective layer
Phosphor layer (Barium Fluorohalide contained in
binder provides photo-stimulable phosphor)
Conduction layer (reduces problem caused by
electrostatic charges by absorbing light and increase
image sharpness)

19. CR Image Acquisition
Phosphor plate
X-ray
system
1. X-ray Exposure
Image
Scaling
3.
Image
Record
4.
Patient
Computed
Radiograph5.
unexposed
Image
Reader
2.
exposed

20. Display / Archive
Laser film printer
DICOM / PACS
Image Acquisition
Latent image produced
CR
Reader
Latent
image
extracted
CR QC
WorkstationPatient information

21. Photostimulated Luminescence
Conduction band
Valence band
PSL
3.0 eV
t Eu
Eu2+
Eu 3+
/
4f 7
8.3 eV
Laser
stimulation
2.0 eV
F/F+
PSLC complexes (F centers) are
created in numbers proportional to
incident x-ray intensity
e-
t tunneling
t recombination
4f 6 5d
phonon
CR: How does it work?
Incident
x-rays
e
Energy Band
BaFBr

22. 300400500600700800
Relativeintensity
0.0
0.5
1.0
 (nm)
Energy (eV)
3 42.521.5
Stimulation and Emission Spectra
1.75
EmissionStimulation
Diode
680 nm
BaFBr: Eu2+
Optical
Barrier

23. Photostimulated Luminescence
Incident Laser Beam
PMT
Protective Layer
Phosphor Layer
Base Support
Light
Scattering
Laser Light Spread
Photostimulated
Luminescence
"Effective" readout diameter
Exposed
Imaging
Plate
Light guide
PSL
Signal

24. CR: Latent Image Readout
PMT
Polygonal
Mirror
Laser
Source
Light channeling guide
Output Signal
Reference
detector Cylindrical mirrorf-
lens
ADC
Laser beam:
Scan direction
Plate translation:
Sub-scan direction
To image
processor
ADC
x= 1279
y= 1333
z= 500

25. CR: Latent Image Readout
PMT
Polygonal
Mirror
Laser
Source
Light channeling guide
Output Signal
Reference
detector Cylindrical mirrorf-
lens
ADC
Laser beam:
Scan direction
Plate translation:
Sub-scan direction
To image
processor
ADC
x= 1279
y= 1333
z= 500

26. Phosphor Plate Cycle
PSP
Base support
reuse
plate erasure:
remove residual signal
light erasure
plate exposure:
create latent image
x-ray exposure
plate readout:
extract latent image
laser beam scan

27. 5 sec scan
Laser Line
Source
Shaping
Lens
Linear CCD
Array
Lens
Array
Line excitation PSL
Sub-scan
Direction
CR “line-scan”
Side View
Linear
Laser
Source
Light Collection Lens
Linear CCD
Array
Stationary IP

28. ADVANTAGES OF C.R.
 Image quality of CR is better than the conventional rare earth screens film
systems
 CR compensates automatically for exposure variations so that images of
optimum density are consistently produced thus eliminating the need of
retakes
 Significant reduction in the exposure factors without the loss of density
 Sharpness of the image is enhanced, due to the usage of needle phosphor
 Computer processing of raw data can produce images of conventional
appearance or if needed, with contrast or sharpness enhancement
 Faster and better post processing.
 Since image data is already in the digital form it can be easily linked to the
PACS.

29. DISADVANTAGES OF C.R.
 High initial cost.
 Radiographers receive no direct feedback
on the accuracy of their exposure
selection, because the resulting CR images
are of consistent density regardless of the
x-ray exposure used.


31. THANK
YOU