digital radiography

AN INTRODUCTION TO DIGITAL RADIOGRAPHY

1. In the Name of God

2. Digital Radiography Lecturer : Seyedeh Shokoofeh M ousavi 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 3/6/2016 Isfahan University of Medical Sciences 3 Table of Content

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 . 3/6/2016 Isfahan University of Medical Sciences 5

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 ) Isfahan University of Medical Sciences 6 3/6/2016

7. Digital Radiology P rocess Image acquisition Image processing Image display Image archiving (PACS) Image retrieving 7 3/6/2016 Isfahan University of Medical Sciences

8. Digital Radiography Systems 3/6/2016 Isfahan University of Medical Sciences 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 3/6/2016 Isfahan University of Medical Sciences 11

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. 3/6/2016 Isfahan University of Medical Sciences 12

13. The principle of PSP Isfahan University of Medical Sciences 13 Excitation Storage Emission CB Trap ADC PMT 3/6/2016

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 3/6/2016 Isfahan University of Medical Sciences 14

15. CR Exposure & Readout 3/6/2016 Isfahan University of Medical Sciences 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 3/6/2016 Isfahan University of Medical Sciences 16

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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 3/6/2016 Isfahan University of Medical Sciences 18

19. Reading Imaging Plate plate is photostimulable phosphor radiation traps electrons in high energy states higher states form latent image H i g h e r E n e r g y E l e c t r o n S t a t e L o w e r E n e r g y E l e c t r o n S t a t e - - - - - - - - - - - - - - - - - - - - - - - - - - - X - R a y P h o t o n - P h o t o n p u m p s e l e c t r o n t o h i g h e r e n e r g y s t a t e 3/6/2016 Isfahan University of Medical Sciences 19

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 Lower Energy Electron State 3/6/2016 Isfahan University of Medical Sciences 20

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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                  3/6/2016 Isfahan University of Medical Sciences 22

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. 3/6/2016 Isfahan University of Medical Sciences 23

24. CCD detectors function 3/6/2016 Isfahan University of Medical Sciences 24

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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 3/6/2016 Isfahan University of Medical Sciences 27

28. Flat panel detector 3/6/2016 Isfahan University of Medical Sciences 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 3/6/2016 Isfahan University of Medical Sciences 29

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 3/6/2016 Isfahan University of Medical Sciences 30

31. Flat Panel Imaging Arrays ( indirect conversion) 3/6/2016 Isfahan University of Medical Sciences 31

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 3/6/2016 Isfahan University of Medical Sciences 32

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. 3/6/2016 Isfahan University of Medical Sciences 33

34. Flat Panel Imaging Arrays ( direct conversion) 3/6/2016 Isfahan University of Medical Sciences 34

35. Direct Vs . Indirect 3/6/2016 Isfahan University of Medical Sciences 35

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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 3/6/2016 Isfahan University of Medical Sciences 37

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 3/6/2016 Isfahan University of Medical Sciences 38

39. C opy display Hard copy display refers to displaying image on film, and soft copy display refers using video monitors. 3/6/2016 Isfahan University of Medical Sciences 39

40. Digital image corrections Dead pixel correction Column defect correction Dark noise correction 3/6/2016 Isfahan University of Medical Sciences 40

41. P rocessing 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. 3/6/2016 Isfahan University of Medical Sciences 41

42. Image Processing based on Convolution The science of manipulating digital images often involves the mathematical operation called “Convolution”.   3/6/2016 Isfahan University of Medical Sciences 42

43. DR properties Adaptive histogram equalization (AHE) Contrast & spatial resolution 3/6/2016 Isfahan University of Medical Sciences 43

44. I'm so glad I live in a world where there are “Autumns”

45. Thanks for your attention