Computed radiography and digital radiography are two methods for obtaining digital x-rays. Computed radiography uses an imaging plate inside a cassette that captures x-rays, which are then digitized in a CR reader. Digital radiography uses a flat panel detector with either direct or indirect conversion of x-rays to electrical signals. Both methods provide advantages over conventional film such as faster workflow, ability to adjust images after exposure, and reduced radiation dose for patients.

1. COMPUTED
RADIOGRAPHY &
DIGITAL
RADIOGRAPHY
Dr Amit

2. Digital X-ray Technology
There are two ways to obtain Digital X-rays:
• Computed Radiography (CR)
• Digital Radiography (DR)

3. What is CR?
• Computed Radiography (CR) is a process of
capturing radiographic data from a
conventional X-ray machine and processing
the data digitally to produce crisp and high
quality radiographic images

4. What is CR?…
• For exposure, an Imaging Plate (IP) is placed in a
cassette instead of a piece of film. The IP captures
and "stores" the X-rays
• The image is "developed" in a CR reader instead
of a film processor. The CR reader extracts the
information stored in the plate and produces a
digital image
• Images produced have much better contrast than a
Conventional X-ray film-screen system

5. Basic Modules of CR
Digitizer
Preview & ID Station
Processing Server
ID Tablet
Laser Camera
Cassette with
Imaging Plate

6. Imaging Plate (IP)
• The Imaging Plate looks like the intensifying
screens found in Conventional film-screen
cassettes
• They are made of photostimulable
phosphor.

7. Imaging Plate (IP)
• Instead of emitting light immediately when exposed
to X-rays, the photostimulable phosphor has the
special property of storing the X-ray energy in a
latent form and releasing the same when stimulated
by a laser energy in the CR Reader / Digitizer

8. Imaging Plate (IP)…
• Storage phosphors are unique because they
respond to a very wide range of X-ray exposures
• This latitude gives the flexibility in selecting
X-ray technique and takes care of under or over
exposure
• Regardless of the exposure, the image can be
displayed correctly
• As a consequence, retakes due to inappropriate
exposures are drastically reduced.

9. Storage phosphor principle
Absorption Emission
laser stimulation
x-rays
electron
trap
electron
trap

10. Storage phosphor principle…
• The imaging plate is coated with
photostimulable phosphor, also called storage
phosphor
• The phosphor material is generally a kind of
Barium fluorohalide
• The Imaging Plate contains not only the
phosphor layer, but also a protective coat, a
conductive layer, support and laminate layers

11. Storage phosphor principle…
• Incident X-rays excite electrons into a higher energy
level (electron traps)
• A latent image is created in the form of “stored energy”
• Stimulation with a scanning laser beam releases
electrons
• Typical wavelength of the stimulating laser is 633 nm
• Falling back, electrons emit luminescent light
• Typical wavelength of the emitted light is 390 nm

12. CR Readout

13. Storage phosphor principle…
• The emitted light intensity is proportional to
the original incident X-ray intensity
• The emitted light is captured with an optical
array and a photomultiplier and is digitized
• The residual image is erased from the plate by
an intense light source, which returns all
electrons to their original stat, making the plate
ready to be reused for new exposures

14. • The storage phosphor plate fits inside a standard
size cassette and is exposed to X-rays exactly like
film
• The X-ray energy is stored on the plate in the form
of latent energy
How is a Storage Phosphor plate
exposed?

15. Patient ID Station
• Before exposing the cassette, the patient
demographic and exam data is stored on the
microchip attached on cassette
• This is done by inserting the cassette in a slot
of ID station and entering the data with the
help of keyboard
• When cassette is inserted in digitizer after
X-ray exposure, the digitizer reads both
patient data as well as X-ray exposure data
• The two data are combined to display images
along with patient data

16. Digitizer
• The plate is inserted into the digitizer
where it is scanned with a high power laser
• The laser light causes the storage
phosphors to release the energy they have
captured in the form of blue light
• In the digitizer, this blue light energy is
converted to electrical signals which are
then digitized to produce digital images

17. What happens to a Storage Phosphor
Plate after it is scanned?
• After exposure and scanning, the phosphor
plate is "erased" by exposing to a bright light
exposure within the digitizer
• The previous image stored in the phosphors is
removed and the plate is ready to be exposed
again

18. Workstation
• The digitized image
data is processed on
a processing server
and is displayed on
its monitor

19. How many times can we use a
Storage Phosphor Plate?
• The life of a phosphor plate depends on
how carefully it is handled. Physical
damage to the plate will limit its useful
life
• If properly cared for, a plate will produce
thousands of images
• Imaging Plates are known to last more
than 50000 Exposure Cycles

20. How is the workflow different with
CR ?
• Instead of taking the film cassette to a dark
room for processing, the technologist takes
the cassette with imaging plate to the CR
reader for digital processing of the image
• Instead of manually taking the films to the
reporting radiologists , the soft copy
images reach the workstation almost
immediately

21. How is the workflow different with
CR ?…
• The time required to acquire a Digital
image is much less compared to
conventional darkroom process
• The film is the first product in Conventional
where as the film is the last product in CR

22. CR WORKFLOW
Rx
Network
Digitizer
Printing
Identification
Processing server
Exposure
Cassette with Imaging Plate

23. Digital Radiography
This technique is performed by digital X-ray
machines with flat panel detectors

24. Digital Radiography
Digital Radiography uses two types of
detectors:
• Direct
• Indirect

25. Direct detectors
• Direct detectors automatically convert X- rays into electronic
signals.
■
■
X.rays interact with semiconductor material
■ Amorphous selenium
X.rays converted directly into electrical charge
■ No intermediate steps

26. Indirect detectors
• Indirect detectors are so named because this technique still uses a
scintillator to converts x-rays to light before conversion to an
electrical charge for subsequent readout.
• X-ray photons encounter a cesium iodide (CsI) scintillator and
are converted to light. The light then reaches a low-noise
photodiode array and is converted into an electrical charge. Each
photodiode represents a single pixel, and each produces an
electrical charge that is read out digitally before finally being sent
to the image processor

27. ■ TFT = THIN-FILM TRANSISTOR ARRAY

28. Limitations of Conventional X-ray process
(X-ray film / Screen/Darkroom)
• Film has a limited exposure latitude i.e less
detail contrast
• Time consuming & cumbersome
• Intolerant to exposure errors
• Repeat X-rays ( More radiation exposure )
• Film wastage

29. Limitations of Conventional X-ray process
(X-ray film / Screen/Darkroom)…
• Cannot be duplicated without loss of quality
• Film storage is a problem
• Scatter radiation reduces contrast and increases
patient dose
• Quality control is an issue

30. What are the advantages of
Digital X-rays?
• Post processing (soft tissue and bony details can
be viewed at same time )
• Reduction in hazardous X-ray dose to patients
• More info on one image
• Constant image quality
• Possibility of viewing X-ray images wherever
needed

31. What are the advantages of
Digital X-rays?…
• Digital images are of extremely high
quality
• Digital images have a future scope of
better image management
• Facility of giving multiple images of
investigative studies on a single high
definition laser film

32. Thank
you