1. Chapter 6: Digital Radiographic Imaging

2. Digital Acquisition Methods
1. Digitize radiographs with a film digitizer

3. * Converts films to
digital files

4. 1. Digitize radiographs with a film digitizer
Digital Acquisition Methods
1. Digitize radiographs with a film digitizer
2. Digitize the video signal with an ADC
Advantages: Inexpensive
Easy to install
Disadvantages: Noisy cameras
Poor signal-to-noise ratio
(200:1, need 1000:1 for digital)
Area beam
Small matrix size

5. Digital Acquisition Methods
1. Scan radiographic films
2. Digitize the video signal
3. Scan projection radiography (SPR)
* Greatly reduces the area of the beam, and scatter
* Replaces the camera with detectors
Fan shaped
beam
Depth of beam
may be a cm, or
smaller

6. Xenon Gas Detector From a CT Scanner
Xenon gas chamber

7. Detectors
1. Xenon Gas
2. Scintillation

8. Detectors 1. Xenon Gas 2. Scintillation Photomultiplier (PM tube)
Crystal

9. Ring of Xenon Detectors in a CT Scanner

10. SPR used for CT Scout Films
X-ray tube
Detectors

11. CT Scout Views
Acquired by SPR, to produce a digital radiograph

12. Digital Acquisition Methods
1. Scan radiographic films
2. Digitize the video signal
3. Scan projection radiography (SPR)
4. Computed Radiography (CR)
Photostimulable image plate (IP) technology
Barium Fluorohalide doped with Europium

13. CR Advantages Uses existing radiographic hardware
Relatively inexpensive to purchase
Reduced number of repeats
Increased latitude
Filmless capture
The CR IP looks
like a conventional
intensifying screen,
and is housed in a
conventional looking
cassette.

14. CR Facts 300 RSV Only one speed (no detail or high speed)
Standard film sizes
Laser Film – wet or dry processing

15. Step 1. Make the exposure like any other radiographic
Computed Radiography
Step 1. Make the exposure like any other radiographic
exposure, only use an IP instead of film.
*Remnant photons strike plate
*Photoelectric interaction causes
barium fluorohalide to fluoresce
as electron is ejected.
*Electrons (that are of no more
use in film radiography) are
trapped in the energy traps
created by the europium IP

16. Reading the IP Converting the stored energy to an
electric current, point by point.

17. The CR IP Reader
And Workstation

18. CR Workstations

19. Posterior bases obscured
Problems Inherent to Conventional Chest Radiography
Under-
exposed
Retrocardiac clear-
space overexposed
Posterior bases obscured
by diaphragm on PA

20. Films

21. Latitude Logarithmic response of film Linear response of CR Maxed out
Yet to respond
Linear response
of CR

22. Analog is continuous. Image is fixed in film Digital is discrete
Analog is continuous. Image is fixed in film Digital is discrete. Image may be manipulated 1 15 15 1

23. CR Postprocessing & Characteristic Curves

24. Histogram

25. Processing Algorithms
Poorly exposed image
plates may be corrected
by software to some extent

26. Patient Dose
Calculated and displayed
Fuji S number (200 ave) Low number = high exposure
Kodak ( ) Low number = low exposure

27. Fuji’s CR Cassette Readers
* Four cassettes
* 115 images per hour
* Standard pixel
density = 5 per mm
* High pixel
density =10 per mm
* Single cassette
* Built in ID terminal
* Single cassette
* Separate ID terminal

28. Cassetteless Readers
Chest units.
In table

29. Workstations Technologists consoles communicates with IP reader for:
* QA of images
* Examination status
* Processing adjustments

30. Laser, Dry Image Hardcopy Devices

31. Now why didn’t they think of that sooner?
Smart CR
All in one unit
Now why didn’t they think of that sooner?

32. Digital Acquisition Methods
1. Scan radiographic films
2. Digitize the video signal
3. Scan projection radiography (SPR)
4. Computed Radiography (CR)
5. Charged Couple Devices
6. Flat Panels
Amorphous Silicon & Amorphous Selenium

33. Thin film transistors (TFT) in an Active Matrix Array (AMA), are incorporated in a “flat panel” detector that is used in place of a film cassette.

34. Thin Film Transistors (TFT)
139 microns (half
a hair)
Diodes connected
to rows
Current flows
out columns

35. Liquid Crystal Displays
5. RGB colored
filters
6. Second filter

36. Amorphous Silicon Cesium iodide (CsI) scintillator
converts X-rays to light
Light is converted to a charge
by a photodiode at a TFT junction.

37. Amorphous Selenium Photon in Interaction creates electron-hole pairs
(called Direct Radiography)
Positive charge
Electrode with a bias voltage
Photoconductor material
Photon in
Negative charge
TFT
Interaction creates
electron-hole pairs
Signal out

38. * Method by which the stored, latent electronic image is discharged
Digital Radiography (DR)
Receptor Reader* Energy Comment
Transformations
Video Target of camera Electron gun x-ray to light to Use limited by
charged globules noise of camera
to video signal
SPR Xenon Interrogations of x-ray to ionized Dedicated cxr
successive detectors electrons and CT scouts
Scintillation Interrogations of x-rays to light
successive detectors to current
CR Photostimulable Helium-neon x-ray to light to Only portable
phosphorIP laser to trapped electrons receptor
to light to current
CCD IC Point by point discharge x-ray to light to Potential next
of photoelectric trapped electrons generation of IIs
detectors (pixels) to current
Amorphous TFT AMA point by point discharge x-ray to light Called direct
silicon Flat panel of TFTs to current radiography
Amorphous TFT AMA point by point discharge x-ray to current Called direct
selenium Flat panel of TFTs radiography
* Method by which the stored, latent electronic image is discharged