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Computed radiography uses a photostimulable plate instead of film that is scanned with a laser to produce a digital radiographic image. The plate contains a phosphor layer that stores radiation energy and emits light when stimulated by the laser, which is then detected and the image digitized. Digital radiography uses a solid-state detector like amorphous selenium that directly converts x-rays to a digital signal in real-time. Both computed radiography and digital radiography allow images to be viewed digitally and integrated into a picture archiving and communication system (PACS) using the DICOM standard.
file004735.ppt
- 1. Computed radiography & Digital Radiography Dr. Muhammad bin zulfiqar PGR-1 SIMS/ SHL.
- 5. 5 Byte The basic unit of binary coded information Kilobyte—210 – 1024 bites Megabyte—1024 times1024bites
- 6. Performance parameters Pixel: Smallest complete sample of an image. Has a varied set of tones in shades of white/ black/grey. Expressed in binary codes (bits). Size of the pixel : Smaller the size , better resolution. CR- 50 to 200 microns, DR- 100 to 200 microns, DM- 50 to 100 microns. Gray Scale: Shades of Gray in between pure black and pure white. Bit Depth: No of shades to define each pixel ,measured as no of bits. Larger the depth, incr gray scale and large file size.
- 7. Spatial Resolution: finer details, diff objects in an image. Depends on sampling frequency and no of pixels. expressed in lp/mm. Contrast Resolution: Color or gray scale differentiation. Indicate the no of shades of grey that a detector can capture. File Size. Performance Parameters(contd..)
- 8. DIGITAL PROJECTION RADIOGRAPHY DEPENDS ON COMPUTER TECHNOLOGY TO PRODUCE DIGITAL RADIOGRAPHIC IMAGE
- 9. DIGITAL PROJECTION RADIOGRAPHY COMPUTED RADIOGRAPHY (CR) DIGITAL RADIOGRAPHY (DR)
- 12. Computed Radiography (CR) Been around since 1980-81 Uses same radiographic equipment No change in X-ray machine Uses an imaging plate Contains a photostimulator phosphor Need a cassette reader Images can be sent to a PACS
- 13. COMPUTED RADIOGRAPHY (CR): USES PHOTOSTIMULABLE PLATE (IMAGE PLATE) INSTEAD OF FILM, AS THE IMAGE RECEPTOR. CR USES CASSETTE THAT LOOKS VERY SIMILAR TO CONVENTIONAL RADIOGRAPHIC CASSETTE.
- 14. Computed Radiography (CR) Re-usable metal imaging plates replace film & cassette Uses conventional bucky & x-ray equipment
- 15. CR SYSTEM COMPONENTS CASSETTES (phosphor plates) ID STATION IMAGE PREVIEW STATION DIGITIZER VIEWING STATION
- 16. CR PLATE !!!!! DOES NOT USE SCREENS OR FILM (CONVENTIONAL FILM)
- 17. CR PLATE
- 18. CASETTE CONSTRUCTION LIGHTWEIGHT ALUMINUM PLASTIC STEEL FRAME FRONT PANEL MADE OF LOW ATTENUATION CARBON FIBER
- 19. CROSS-SECTION OF CR PLATE PROTECTIVE LAYER PHOSPHOR LAYER ANTI-HALO & REFLECTIVE LAYER BASE BACKING LAYER
- 20. PHOSPHOR LAYER BASE Ba FX: Eu +2 PET- POLYETHYLENE TERAPHTALATE PROTECTIVE LAYER FLUORINATED POLYMER MATERIAL PROTECTS PHOSPHOR LAYER
- 21. ANTI-HALO LAYER + REFLECTIVE LAYER PREVENTS LASER FROM PASSING THROUGH. REFLECTED LIGHT FROM PHOSPHOR IS ALLOWED TO PASS. BACKING LAYER PROTECTS THE BASE FROM DAMAGE.
- 23. CR CASSETTE IS PROTECTING IMAGE PLATE FROM DAMAGE + IS THE STABLE VEHICLE FOR TRANSPORT AND PLACEMENT OF THE CASSETTE UNDER THE PATIENT
- 24. BACK PANEL CONTAINS LEAD FOIL TO PROTECT THE PLATE FROM BACKSCATTER !!! BACK PANEL ALSO CONTAINS CHIP TO RECORD PATIENT DEMOGRAPHIC INFORMATION
- 28. CR Operation
- 29. Add module code number and lesson title 29 (Europium Activated Barium FluoroHalide) BaFX:Eu , (X= Cl, Br, or I)
- 30. Add module code number and lesson title 30 The principle of PSP Excitation Storage Emission CB Trap ADC PMT
- 31. Impurities in the crystal lattice are responsible for luminescence. As the concentration of impurity ions increase the greater the intensity of the luminescence. CR screens use barium fluorohalides doped with europium (europium is the impurity in the crystal). LUMINESCENCE
- 32. When phosphors are stimulated with x-ray photon energy electron pair holes are created. In effect, europium is raised to an excited state and upon luminescence it is returned to its ground Eu2+ state. This mechanism holds for both spontaneous luminescence and photostimulated luminescence LUMINESCENCE
- 33. H igher E nergy E lectron State Lower E nergy Electron State - - - - - - - - - - - - - - - - - - - - - - - - - - - X-R ay P hoton - P hoton pumps electron to higher energy state
- 34. The shifting of europium from its excited state back to its ground state for both spontaneous and photostimulated luminescence is about 0.6 - 0.8 microseconds. With screen-film imaging these crystals spontaneously luminescence to expose a film, but with CR imaging the luminescence occurs, then there is also photoluminescence that occurs when the screen is stimulated by a narrow beam of infrared light. LUMINESCENCE
- 35. The holes or vacancies in the lattice are portions of the lattice normally occupied by halogens (fluoride, bromide, or iodine). These vacancies will trap free electrons when irradiated and are called Farbzentren centers or F- centers. When the photostimulable plate is exposed to high frequency light, usually from a helium laser, the electrons in these F-centers are liberated and cause luminescence at readout. LUMINESCENCE
- 36. Add module code number and lesson title 36 (Images courtesy of AFGA) PSP digitizer Casette and PSP Workstation
- 37. 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 Laser Beam Higher Energy Elect ron St at e Lower Energy Elect ron St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - Lower Energy Electron State
- 38. 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 Reading Imaging Plate
- 40. THE LATENT IMAGE WILL REMAIN STORED FOR 24 HOURS. IT WILL FADE THROUGH PHOSPHORESCENCE FADING 25% OF STORED ENERGY WITHIN 8 HOURS
- 41. CR PLATE CR SCANNER/READER CR AFTER EXPOSURE IS INSERTED INTO CR SCANNER
- 42. READOUT THE SCANNER SCANS THE IMAGE PLATE WITH LASER LIGHT AND READS THE LATENT IMAGE FROM THE PHOSPHOR
- 43. CR Exposure & Readout
- 45. LASER HELIUM-NEON (633 nm) LASER BEAM SWEEPS THE PLATE IN RASTER FASHION
- 47. PLATE & F-CENTERS LASER 633 nm PHOTOSTIMULABLE LUMINESCENCE 390-400 nm
- 48. LASER SPOT SIZE – 100 MICROMETERS PIXEL SIZE – 100 MICROMETERS
- 49. P.M. TUBE DETECTION SENSITIVITY MATCHED TO BLUE-PURPLE PSL (390-400 nm)
- 50. AFTER SCANNING THE CR PLATE NEED TO BE CLEARED FROM RESIDUAL SIGNAL PLATE EXPOSED TO HIGH INTENSITY SODIUM VAPOR OR FLUORESCENT LIGHT
- 52. After read-out, plate erased using a bright light Plate can be erased virtually without limit Plate life defined not by erasure cycles but by physical wear
- 53. IMAGE DISPLAY Typical image plate can be reused thousands of times
- 54. CR Resolution Small cassettes have better spatial resolution Smaller pixels More pixels / mm
- 58. PACS
- 59. CR CHARACTERISTIC CURVE VERY WIDE LATITUDE CR SYSTEMS LESS RADIOGRAPH REPEATS
- 60. Much greater latitude than screen/film Plate responds to many decades of input exposure under / overexposures unlikely Computer scale inputs exposure to viewable densities Unlike film, receptor separate from viewer
- 61. CHARACTERISTIC CURVE LATITTUDE OF CR LATITTUDE OF FILM
- 62. IMAGE CAN BE SALVAGED WITH CR 500% OVEREXPOSURE 80% UNDEREXPOSURE USE ADEQUATE KVP
- 63. HARD COPY GENERATED IN LASER PRINTER
- 64. CR SYSTEM EFFICIENCY CHARACTERISTIC QDE- QUANTUM DETECTION EFFICIENCY NO NEED FOR SCREENS QDE: THE MEASURE OF THE EFFICIENCY OF CR SYSTEM TO CONVERT REMNANT X-RAYS TO USEFUL IMAGE SIGNAL QDE PATIENT DOSE
- 66. Receptor provides direct digital output No processor / reader required Images available in < 15 seconds Much less work for technologist
- 72. 72 CCD Based Detection System
- 77. PACS and DICOM THE ROLE OF PACS : A Picture Archiving and Communication System (PACS) aims to replace conventional analogue film and paper clinical request forms and reports with a completely computerized electronic network whereby digital images are viewed on monitors in conjunction with the clinical details of the patient and the associated radiological report displayed in electronic format. The ROLE OF DICOM: Digital Imaging and Communications in Medicine (DICOM) is a standard for handling, storing, printing, and transmitting information in medical imaging. It includes a file format definition and a network communications protocol. DICOM enables the integration of scanners, servers, workstations, printers, and network hardware from multiple manufacturers into a picture archiving and communication system (PACS). The different devices come with DICOM conformance statements which clearly state the DICOM classes they support. DICOM has been widely adopted by hospitals .
- 79. ?