AN INTRODUCTION TO DIGITAL RADIOGRAPHY

2. Lecturer : Seyedeh Shokoofeh Mousavi Gazafroudi
3/6/2016 Isfahan University of Medical Sciences 2

3.  Introduction to digital radiography(DR)
 Process
 System
 classification
 Computed Radiography (CR)
 photostimulable phosphor (PSP)
 Exposure & readout
 Imaging plates
 Charged Couple Device (CCD)
 Indirect Digital Radiography (IDR)
 Structure & function
 Direct Digital Radiography (DDR)
 Structure & function
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4. Introduction to digital radiography(DR)
Process
System
classification

5. Introduction
 Historically, digital radiography referred to specialized modalities that
produced digital images
 Digital images can be numerically processed This is not possible in
conventional radiology.
 Digital images can be easily transmitted through networks and
archived
 Since the early 1990s, Digital Radiography has grown to include
Computed Radiography(CR) and ‘true’ Digital Radiography(DR) or
Direct Radiography.
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6. What is digital radiology?
 In conventional radiographic images, spatial position and blackening are
analogue values
 Digital radiology uses a matrix to represent an image
 A matrix is a square or rectangular area divided into rows and columns. The
smallest element of a matrix is called ”pixel”
 Each pixel of the matrix is used to store the individual grey levels of an image,
which are represented by positive integer numbers
 The location of each pixel in a matrix is encoded by its row and column number
(x,y)
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7. Digital Radiology Process
 Image acquisition
 Image processing
 Image display
 Image archiving (PACS)
 Image retrieving
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8. Digital Radiography Systems 8

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10. Computed Radiography (CR)
photostimulable phosphor (PSP)
Exposure & readout
Imaging plates
Charged Couple Device (CCD)

11. Computed Radiography (CR)
 Uses same radiographic equipment
 No change in X-ray machine
 Uses an imaging plate
 Contains a photo stimulator phosphor
 Need a cassette reader
 Images can be sent to a PACS
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12. Computed Radiography
 Is a marketing term for photostimulable phosphor (PSP) detector systems.
 Re-usable metal imaging plates replace film & cassette
 Uses conventional bucky & x-ray equipment
 When x-rays are absorbed some light is promptly emitted, but much of the
absorbed x-ray energy is trapped in the PSP screen and can be readout later.
 CR imaging plates are made of barium fluorohalid.
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13. The principle of PSP 13
Excitation Storage Emission
CB
Trap
ADC
PMT

14. CR readout processing steps
 After the cassette is exposed by the x-ray beam, the cassette is loaded into a
reader.
 The reader removes the phosphor plate and exposes it to a laser, stimulating
the phosphors.
 The light emitted from the plate is collected, quantified, and digitized.
 after read-out, plate erased using a bright light
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15. CR Exposure & Readout 15

16. Reading Imaging Plate
 Reader scans plate with laser
light using rotating mirror
 Film pulled through scanner by
rollers
 Light given off by plate
measured by PM tube &
recorded by computer
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17. PMT
Beam deflector
Laser
Source
Light channelingguide
Plate translation:
Sub-scan direction
Laser beam:
Scandirection
Output Signal
Reference detector
Beam splitter
Cylindrical mirrorf-theta
lens
Amplifier
ADC
Toimage
processor
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18. Laser & Emitted Light are Different Colors
 Phosphor stimulated by laser light
 Intensity of emitted light indicates amount of
radiation incident on phosphor at each location
 Only color of light emitted by phosphor measured
by PMT
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19. Reading Imaging Plate
 plate is photostimulable
phosphor
 radiation traps electrons in
high energy states
 higher states
form latent image
Higher Energy
Electron
State
Lower Energy
Electron
State
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X-Ray
Photon
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Photon pumps
electron to
higher energy state
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20. Reading Imaging Plate
 reader scans plate with laser
 laser releases electrons trapped in high
energy states
 electrons fall to low energy states
 electrons give up energy as visible light
 light intensity is measure of incident
radiation
Laser Beam
Higher Energy
Elect ron
St at e
Lower Energy
Elect ron
St at e
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Lower Energy
Electron State
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21. 21

22. CR Throughput
 Generally slower than film processing
 CR reader must finish reading one plate
before starting to read the next
 Film processors can run films back to back
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23. Charged Couple Device (CCD)
 Is an integrated circuit made of crystalline silicon
 Forms images from visible light
 For linear CCD detectors charge pocket at the very bottom of linear array spills onto a
transistor, and produce an electronic signal that is digitized. The entire line of pixels and
readout in a shift-and-read process.
 For 2D CCD detectors , the charges on each column are shifted onto the bottom row of
pixels, that entire row is read out horizontally, and then next charges from all columns are
shifted down one pixel.
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24. CCD detectors function 24

25. 25

26. Indirect & Direct Digital Radiography
(IDR & DDR)

27. Digital Radiography (DR)
 Receptor provides direct digital output
 Potentially lower patient dose than CR
 High latitude as for CR
 No processor / reader required
 Images available in < 15 seconds
 Much less work for technologist
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28. Flat panel detector 28

29. Indirect digital radiography
 X-ray strike scintillator producing light
 Photodiode array converts light to electrons
 The intensifying screen is made up of cesium-iodide crystals and the
photodetector is made up of amorphous silicon.
Light
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30. Indirect digital radiography
 Electronic sensor are replaces the light sensitive film emulsion
 X-rays are absorbed in the screen and the absorbed energy is then relayed to
the photodetector by visible light photons
 The ratio of the light sensitive area to the entire area of each detector element
is called fill factor
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31. Flat Panel Imaging Arrays (indirect conversion)
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32. Direct Digital Radiography
 Is made from a layer of photoconductor materials on top of a TFT array
 The electrons released in the detector layer from x-ray interaction are used
to form the image directly
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33. Direct DR
 the photoconductor is made up of amorphous selenium. selenium has
higher atomic number than silicon, but it is still quit low compared with
conventional x-ray intensifying screen phosphorus.
 Due to electric field ,selenium direct detectors can be made much thicker.
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34. Flat Panel Imaging Arrays (direct conversion)
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35. Direct Vs. Indirect
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36. 36

37. Digital mammography
 it uses a mosaic of CCD and CsI
scintillator.
 As scanning x-ray beam detector
move to the right , the charge
packet in the CCD array are moving
to the left
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38. Patient dose considerations
 The exposure necessary to produce good images are directly related to
the detective quantum efficiency of the detector (DQE)
 CR systems require about twice the exposure of a corresponding 400-
speed screen-film detector for comparable image quality
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39. Copy display
 Hard copy display refers to displaying image on film, and soft copy
display refers using video monitors.
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40. Digital image corrections
 Dead pixel correction
 Column defect correction
 Dark noise correction
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41. Processing
 Is performed by altering the relation between digital number in the image
and displayed brightness
 Windowing, leveling & reversing the contrast are simple procedures
performed routinely.
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42. Image Processing based on Convolution
 The science of manipulating digital images
often involves the mathematical operation
called “Convolution”.
 𝑔 𝑥 = −∞
+∞
𝐼 𝑥’ ℎ 𝑥 − 𝑥’ 𝑑𝑥’
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43. DR properties
 Adaptive histogram equalization (AHE)
 Contrast & spatial resolution
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44. I'm so glad I live in a world where there are
“Autumns”