Computed Radiography and digital radiography

Computed and digital radiography

1. SEMINAR COMPUTED RADIOGRAPHY (CR) a nd DIGITAL RADIOGRAPHY (DR) Moderator – Dr Anil Rawat Presenter – Dr Durga Singh 14/07/21

2. Overview : Introduction Components Principle Working Advantages Disadvantages CR & DR

3. Computed Radiography (CR)

4. It is the digital replacement of conventional X-ray film radiography It is the process of capturing radiographic data from a conventional x-ray machine and processing the data digitally to produce high quality radiographic images 1973 – KODAK patented the first optically scanned storage phosphor system (CR) 1983 – FUJI commercialized firstly CR Basically the bridge between the conventional and the digital technology Introduction Introduction – components – principle – working – advantages - disadvantages

5. Components Introduction – components – principle – working – advantages - disadvantages Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system Video

6. Principle Introduction – components – P rinciple – working – advantages - disadvantages CR employs a phosphor ( present in the IP ) , which works on PSL ( Photo- stimulable luminescence )principle When the phosphor is exposed to radiation , it absorbs the radiation and store the energy . Amount of luminescence Radiation exposed Later , when it is exposed by a different light source , it gives luminescence

7. Principle Introduction – components – principle – working – advantages - disadvantages CR employs a phosphor ( present in the IP ) , which works on PSL ( Photo- stimulable luminescence ) principle When the phosphor is exposed to radiation , it absorbs the radiation and store the energy . Later , when it is exposed by a different light source , it gives luminescence Amount of luminescence Radiation exposed

8. Introduction – components – P rinciple – working – advantages - disadvantages

9. Components Introduction – components – principle – working – advantages - disadvantages Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system

10. Introduction – components – principle – working – advantages - disadvantages Components Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system Imaging acquisition system / Imaging P late (IP) In CR , image is captured in thin plastic sheet , k/a Imaging plate ( similar to conventional screen film cassette ) Available in different sizes – 14x17’’ ,14x14’’, 10x12’’, 8x10’’ Made up of several layers :

11. Introduction – components – principle – working – advantages - disadvantages Components Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system Imaging acquisition system / Imaging P late (IP) made up of several layers : Protective layer – thin,tough,clear plastic that protects the phosphor/active layer of IP Phosphor/Active layer – layer of photostimulable phosphor that traps electrons during exposure , this layer has the property of storing radiation energy for a while. This is usually made of phosphors from bariumfluorohalide family- generally – BaFBr (85%) + BaFI (15%) : Eu . This Eu is doped in bariumfluorohalide crystals which acts like an activator for PSL property and create defects in the crystals for trapping electrons Reflective layer – reflects the light to the reader Conductive layer – absorbs light as well as any electrical charge Supportive layer – made of polyester and gives some strength to IP

12. Introduction – components – principle – working – advantages - disadvantages Imaging plate reader/Phosphor reader Most critical part of CR imaging system After the radiation exposure , the CR cassette is inserted into the reader , where the IP is removed and fitted into drive mechanism Components Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system

13. After the radiation exposure , the CR cassette is inserted into the reader , where the IP is removed and fitted into drive mechanism The drive mechanism moves the plate with constant velocity along the y-axis. This is usually done with slow motion – k/a slow scan mode . A rotating and multi-faced mirror reflects the red light from a laser light source (He Ne laser 633nm) This light is deflected back and forth across the phosphor plate in the horizontal (x axis) which releases visible wavelength , blue green light of 390nm . This is done by fast scan mode The blue green light is collected by the photomultiplier tube (PMT) through the fiber optic light guide The PMT amplifies the signal and gives the output electronic signal , which is fed into the computer for further processing

14. Introduction – components – principle – working – advantages - disadvantages Imaging plate reader/Phosphor reader After the radiation exposure , the CR cassette is inserted into the reader , where the IP is removed and fitted into drive mechanism The drive mechanism moves the plate with constant velocity along the y-axis. This is usually done with slow motion – k/a slow scan mode . A rotating and multi-faced mirror reflects the red light from a laser light source (He Ne laser 633nm) This light is deflected back and forth across the phosphor plate in the horizontal (x axis) which releases visible wavelength , blue green light of 390nm . This is done by fast scan mode Both fast and slow scan modes are controlled by the CR computer Components Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system

15. Introduction – components – principle – working – advantages - disadvantages Imaging plate reader/Phosphor reader The blue green light is collected by the photomultiplier tube (PMT) through the fiber optic light guide The PMT amplifies the signal and gives the output electronic signal , which is fed into the computer for further processing The CR reader takes around 110 sec to process each cassette Components Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system

16. Introduction – components – principle – working – advantages - disadvantages Components Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system 3 . Image display system

17. Introduction – components – principle – working – advantages - disadvantages Components Image acquisition system / Imaging plate (IP) Imaging plate reader Image display system Image storage system 4. Image storage system After display of image , image can be stored or printed The image is stored in the computer hard disk and from this storage system , we can retrieve the image whenever we want

18. Working Introduction – components – principle – Working – advantages - disadvantages Based on PSL principle The material which has the property of giving luminescence is k/a phosphor When the IP/phosphor is exposed to radiation , the divalent europium atoms get oxidized into trivalent europium ion with release of electrons in valence bond These electrons move from valence bond to conduction band , later they are trapped at the F centres in the forbidden zone. These electrons can stay in these centres for longer period of time When the IP is scanned by red laser light , the F centres absorbs energy and transfer it to the electrons Then electrons move from conduction band to valence band with emission of blue green light The electrons joins with trivalent europium and converted into divalent europium

19. Working Introduction – components – principle – working – advantages - disadvantages Based on PSL principle The material which has the property of giving luminescence is k/a phosphor When the IP/phosphor is exposed to radiation , the divalent europium atoms get oxidized into trivalent europium ion with release of electrons in valence bond These electrons move from valence bond to conduction band , later they are trapped at the F centres in the forbidden zone. These electrons can stay in these centres for longer period of time When the IP is scanned by red laser light , the F centres absorbs energy and transfer it to the electrons Then electrons move from conduction band to valence band with emission of blue green light The electrons joins with trivalent europium and converted into divalent europium

20. Working Introduction – components – principle – working – advantages - disadvantages The phosphor will not give up all the trapped electrons in the first laser light exposure. It will retain some amount of trapped electrons. Hence , it is exposed to a very bright light source , which moves all the trapped electrons to the valence bond, thus emptying the F centres. Now the phosphor can be used for radiation exposure

21. Advantages Wide , dynamic range Improved image quality Less patient dose Images can be stored No chemicals required Less time taking as compared to conventional radiography Introduction – components – principle – working – advantages - disadvantages Disadvantages High equipment cost Higher noise Spatial resolution is less compared to conventional radiography

22. Introduction – components – P rinciple – working – advantages - disadvantages Summary

23. Digital Radiography (DR)

24. It is a technique in which conventional silver halide film or PSP screen like radiation receptors are replaced by photo electronic receptor which is connected directly to computer. Introduction Introduction – components – principle – working – advantages - disadvantages

25. Components Introduction – components – principle – working – advantages - disadvantages X-ray equipment Detector TFT (Thin Film Transistor) CCD (Charge couple devices) Computer system Video

26. Principle Introduction – components – principle – working – advantages - disadvantages X-ray signals can be digitized by using detectors X-rays falls on detectors which convert x-ray signal into electronic signal These electronic signal falls on TFT or CCD where they are converted into digital signals

27. Principle Introduction – components – principle – working – advantages - disadvantages X-ray signals can be digitized by using detectors X-rays falls on detectors which convert x-ray signal into electronic signal These electronic signal falls on TFT or CCD where they are converted into digital signals These digital signals are displayed as image on the computer system

28. Introduction – components – principle – working – advantages - disadvantages

29. Components Introduction – components – principle – working – advantages - disadvantages X-ray equipment – X-ray machine same as conventional /CR X-ray machine High power generators are used Detector – Main function is to convert x-ray signal into electronic signal Indirect or direct digital detector Components X-ray equipment Detector TFT (Thin Film Transistor) CCD (Charge couple devices) Computer system

30. Introduction – components – principle – working – advantages - disadvantages Indirect digital detector Amorphous Silicon photodiode : light sensitive material Function : light signal to electronic signal Consists of scintillation Phosphor crystal and Amorphous Silicon photodiode Scintillation Phosphor crystal used : Thallium activated cesium iodide ( CsI:Tl ) , terbium activated gadolinium oxy sulfide (Gd2O2S:Tb) Function : X-ray signal to light photons X-ray photons Light photons Electronic signal Scintillation Phosphor crystal Amorphous Silicon photodiode

31. Introduction – components – principle – working – advantages - disadvantages Direct digital detector Consists of Amorphous Selenium photo conducting material X-ray photons Electronic signal Amorphous Selenium photo conducting layer

32. Introduction – components – principle – working – advantages - disadvantages 3. Thin film transistor (TFT) / Flat panel detector (FPD) Components X-ray equipment Detector TFT (Thin Film Transistor) CCD (Charge couple devices) Computer system It can be used with both direct or indirect digital detector It has 3 connections : Source – capacitor Gate – connected to horizontal lines (rows) Drain – connected to vertical or read out lines (columns)

33. TFT is basically an electronic switch that can be made ON and OFF - ve voltage applied to gate – OFF + ve voltage applied to gate – ON Initially , the capacitor of each detector element that stores the charge is earthened , so that all the residual charges are passed on ground During the x-ray exposure , - ve voltage to gate – TFT in OFF position – charge accumulated in each detector element is stored in capacitor During the read out process, + ve voltage to gate (one row R at a time) – thus the switches of detector elements in a given row are ON This will connect vertical wires C1 & C2 to multiplexer through switches S1 & S2 Multiplexer select the coloumn sequentially ( one coloumn at a time ) and charge is amplified and allowed to move to digitizer

34. Introduction – components – principle – working – advantages - disadvantages TFT is basically an electronic switch that can be made ON and OFF - ve voltage applied to gate – OFF + ve voltage applied to gate – ON Initially , the capacitor of each detector element that stores the charge is earthened , so that all the residual charges are passed on ground During the x-ray exposure , - ve voltage to gate – TFT in OFF position – charge accumulated in each detector element is stored in capacitor During the read out process, + ve voltage to gate (one row R at a time) – thus the switches of detector elements in a given row are ON This will connect vertical wires C1 & C2 to multiplexer through switches S1 & S2 Multiplexer select the coloumn sequentially ( one coloumn at a time ) and charge is amplified and allowed to move to digitizer

35. Introduction – components – principle – working – advantages - disadvantages Thus Gate --------------- Row Multiplexer ------- Coloumn and charge in each detector element is read out sequentially Finally , Electronic signal --------- digitized --------- stored

36. Introduction – components – principle – working – advantages - disadvantages 4. Charged coupled devices (CCD) CCD forms images from visible light It is usually used with intensifying screens and image intensifier tubes CCD is an integrated circuit made up of MOCSC- metal oxide crystalline silicon capacitor CCD has individual pixel elements ; when visible light falls on each pixel ; electrons are liberated charges from pixels Electrons in every pixel are shifted to another pixel The bottom row is read out pixel by pixel and the charge is shifted to the read out electronics ; which produces an electronic signal This signal is digitized by ADC and will be used to construct final image matrix

37. Introduction – components – principle – working – advantages - disadvantages 4. Charged coupled devices (CCD) CCD forms images from visible light It is usually used with intensifying screens and image intensifier tubes CCD is an integrated circuit made up of MOCSC- metal oxide crystalline silicon capacitor CCD has individual pixel elements ; when visible light falls on each pixel ; electrons are liberated charges from pixels Electrons in every pixel are shifted to another pixel The bottom row is read out pixel by pixel and the charge is shifted to the read out electronics ; which produces an electronic signal This signal is digitized by ADC and will be used to construct final image matrix

38. Introduction – components – principle – working – advantages - disadvantages Components X-ray equipment Detector TFT (Thin Film Transistor) CCD (Charge couple devices) Computer system In the computer system , the digital image is manipulated by different means like contrast enhancement , brightness control etc From this computer system , the digital image will go to either printer system or in the storage system 5. Computer system

39. Working Introduction – components – principle – working – advantages - disadvantages Indirect digital detector Direct digital detector

40. Advantages No chemicals required for image processing Elimination of dark room Instant viewing of images Less radiation dose to the pt Ability to manipulate the image Better image quality Introduction – components – principle – working – advantages - disadvantages Disadvantages More expensive Sensors can be bulky for the pt

41. Introduction – components – P rinciple – working – advantages - disadvantages Summary

42. CR DR Components - cassette – labour intensive step Cassette reading takes time Can view images after few time Cassette can’t be used immediately Lower initial investment Lower image quality Components – detectors - no labour Immediate reading Can view images instantly Detectors can be used immediately Higher initial investment Higher image quality vs

43. MCQ session

44. Q1. Tungsten is most likely used as an x-ray target because of its high A. Physical density B. Electron density C. Electrical resistance D. Melting point Reference : The physics of radiology and imaging , K Thayalan , Chapter 3 – Physics of x-rays , page no 59

45. Q1. Tungsten is most likely used as an x-ray target because of its high A. Physical density B. Electron density C. Electrical resistance D. Melting point

46. Q2. Material responsible photo- stimulable luminescence in CR A. Barium B. Fluorine C. Bromide D. Europium Reference : The physics of radiology and imaging , K Thayalan , Chapter 8 – computed and digital radiography , page no 189

47. Q2. Material responsible photo- stimulable luminescence in CR A. Barium B. Fluorine C. Bromide D. Europium

48. Q3. The function of optical filter placed in front of PMT in CR is A. To attenuate scattered laser light B. To attenuate blue-green light C. No function D. To amplify the blue-green ligh Reference : The physics of radiology and imaging , K Thayalan , Chapter 8 – computed and digital radiography , page no 193

49. Q3. The function of optical filter placed in front of PMT in CR is A. To attenuate scattered laser light B. To attenuate blue-green light C. No function D. To amplify the blue-green ligh

50. Q4. The most preferred scintillation crystal used in indirect detectors is made up of A. CsI:Tl B. Gd2O2S:Tb C. Amorphous Silicon D. None Reference : The physics of radiology and imaging , K Thayalan , Chapter 8 – computed and digital radiography , page no 199

51. Q4. The most preferred scintillation crystal used in indirect detectors is made up of A. CsI:Tl B. Gd2O2S:Tb C. Amorphous Silicon D. None

52. Q5. Direct detectors in DR can use A. TFT B. CCD C. Both D. None Reference : The physics of radiology and imaging , K Thayalan , Chapter 8 – computed and digital radiography , page no 195

53. Q5. Direct detectors in DR can use A. TFT B. CCD C. Both D. None

54. Q6. If KVP is increased , subject contrast A. Increases B. Decreases C. No effect D. None Reference :

55. Q6. If KVP is increased , subject contrast A. Increases B. Decreases C. No effect D. None

56. Q7. The sequence of equipments in CR is A. X-ray tube - grid - pt - imaging plate - computer - reader B. X-ray tube - pt - grid - imaging plate - reader - computer C. X-ray tube - pt - grid - imaging plate - computer - reader D. X-ray tube - grid - pt - imaging plate - reader - computer Reference : The physics of radiology and imaging , K Thayalan , Chapter 8 – computed and digital radiography , page no 191

57. Q7. The sequence of equipments in CR is A. X-ray tube - grid - pt - imaging plate - computer - reader B. X-ray tube - pt - grid - imaging plate - reader - computer C. X-ray tube - pt - grid - imaging plate - computer - reader D. X-ray tube - grid - pt - imaging plate - reader - computer

58. Q8. Which of the following is NOT an advantage of CR A. Imaging plates are reusable B. Darkroom and chemical processing not required C. Easy storage of digital information D. Cheaper than screen film radiography Reference :

59. Q8. Which of the following is NOT an advantage of CR A. Imaging plates are reusable B. Darkroom and chemical processing not required C. Easy storage of digital information D. Cheaper than screen film radiography

60. Q9.Grids are placed between A. X-ray source and pt B. Pt and cassette C. Detector and TFT D. Detector and CCD Reference : The physics of radiology and imaging , K Thayalan , Chapter 7 – screen film radiography , page no 160

61. Q9.Grids are placed between A. X-ray source and pt B. Pt and cassette C. Detector and TFT D. Detector and CCD

62. Q. If a grid is manufactured with 30 micrometers lead strips sandwitched between interspace material that is 300 micrometers thick with a height of 2.4mm. What is grid ratio ? 5:1 b. 8:1 c. 16:1 d. 4:1 Reference : The physics of radiology and imaging , K Thayalan , Chapter 7 – screen film radiography , page no 160

63. Q. If a grid is manufactured with 30 micrometers lead strips sandwitched between interspace material that is 300 micrometers thick with a height of 2.4mm. What is grid ratio ? 5:1 b. 8:1 c. 16:1 d. 4:1

64. Thank you ! By – Dr Durga Singh