1 / 72

COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION

COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION. OUTLINE. CT SYSTEM COMPONENTS – DEFINITION OF A SCANNER SCANNER COORDINATE SYSTEM – XYZ, ISOCENTER IMAGING SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, AND STORAGE SYSTEMS. CT MAIN SYSTEMS. IMAGING SYSTEM COMPUTER SYSTEM

tiponya
Download Presentation

COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION

  2. OUTLINE • CT SYSTEM COMPONENTS – DEFINITION OF A SCANNER • SCANNER COORDINATE SYSTEM – XYZ, ISOCENTER • IMAGING SYSTEM • COMPUTER SYSTEM • DISPLAY, RECORDING, AND STORAGE SYSTEMS

  3. CT MAIN SYSTEMS • IMAGING SYSTEM • COMPUTER SYSTEM • DISPLAY, RECORDING, STORAGE SYSTEM • DATA ACQUISITION SYSTEM

  4. CT SYSTEM GANTRY X-RAY TUBE GANTRY CONTROL DETECTORS HIGH VOLTAGE GENERATOR DAC S/H ADC SCAN CONTROLLER ARRAY PROCESSOR HOST COMPUTER CONSOLE STORAGE

  5. SCANNER

  6. SCANNER • GANTRY • PATIENT COUCH

  7. GANTRY HOUSES: • X-RAY TUBE • GENERATOR (LOW VOLTAGE DESIGN) • COLLIMATORS • DETECTORS

  8. GANTRY CHARACTERISTICS • APERTURE • TILTING RANGE

  9. MOST OF THE SCANNERS HAVE 70CM APERTURE

  10. 70 CM

  11. COORDINATE SYSTEM X

  12. COORDINATE SYSTEM Y

  13. COORDINATE SYSTEM Z

  14. ISOCENTER

  15. TILTING RANGE OF MOST SCANNERS- +30 TO -30 DEGREES

  16. PATIENT COUCH :450 LBS (204 KG) DISTRIBUTED WEIGHT LIMIT

  17. SCANNABLE RANGE:COVERAGE FROM HEAD TO THIGH (162CM)

  18. MAX. SCANNABLE RANGE

  19. IMAGING SYSTEM • PRODUCTION OF X-RAYS • SHAPING OF X-RAY BEAM ENERGY • FILTERING X-RAY BEAM

  20. IMAGING SYSTEM COMPONENTS • X-RAY TUBE • GENERATOR –HIGH VOLTAGE • COLLIMATORS • FILTER • DETECTORS • DETECTOR ELECTRONICS

  21. X-RAY TUBE AND X-RAY PRODUCTION

  22. CATHODE --------MADE OF TUNGSTEN IN CT – STILL SMALL AND LARGE

  23. THERMIONIC EMISSION CATHODE HEATED UP TO AT LEAST 2,200 DEG. CELSIUS TO LIBERATE ELECTRONS FOR TRANSIT TO ANODE

  24. FOCAL SPOT- CT UTILIZES DIFFERENT FOCAL SPOTS • THE FILAMENT SIZE – LENGTH – FOCAL SPOT SMALLER FOCAL SPOT - Low mA SMALLER FOCAL SPOT – sharper image

  25. ANODE +++++ MADE OF TUNGSTEN AND MOLYBDENUM TUNGSTEN TARGET TARGET MADE OF TUNGSTEN AND RHENIUM

  26. mA – tube current • The number of electrons flowing from cathode to anode

  27. kVp • Potential difference between cathode and anode (Volts) kilo means 1,000 x.

  28. S –time of exposuremAs tube current for certain length of time

  29. X-RAY PRODUCTION RESULTS IN A LOT OF HEAT AND VERY LITTLE X-RAYS BEING GENERATED HEAT UNITS CALCULATION HU= kVp X mA x time MOST CT TUBES HEAT CAPACITY 3-5 MILLION HU

  30. REDUCTION OF HEAT UNITS – TECHNIQUE COMPENSATION • kVp • mA • Time INCREASED NOISE

  31. TOO LOW OF kVp: • NOISE !!!!

  32. X-RAY EMISSION

  33. TUBE CURRENT CHANGE INTENSITY ENERGY – NO CHANGE CURRENT 2 * mA = 2 * number of photons 4 * mA = 4 * number of photons

  34. Why changing mA or time • Avoiding motion – mA time • Pediatric technique modification • Reducing noise - mAs MOTION NOISE

  35. Tube voltage (kVp) CHANGE INTENSITY - ENERGY– kVp 15% INCREASE OF KVP = 2 * mAs

  36. kVp IN CT • 80-140 • TOO LOW – NOISE (NOT ENOUGH PENETRATION OF THE PATIENT ) PHOTON STARVATION - NOISE!!!!!

  37. HIGH VOLTAGE GENERATOR –(HVG) • GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBE

  38. CT GENERATOR • 5-50 kHz • 30-60 kW KVP SELECTION: 80, 100, 120, 130,140 mA selection: 30, 50, 65, 100, 125, 150, 175, 200, 400

  39. COLLIMATION IN CT PRE-PATIENT COLLIMATION POST-PATIENT COLLIMATION ADC

  40. BASIC DATA AQUSITION SCHEME IN CT FILTRATION ADC

  41. FILTRATION CHANGE INTENSITY ENERGY – FILTRATION

  42. FILTRATION MATERIAL • ALUMINIUM ( SPECIAL FILTER IN CT) BOWTIE TO MAKE THE BEAM HARDER AND MORE MONOENERGETIC

  43. Filter DEFINES SLICE THICKNESS Patient REDUCES SCATTER RECHING THE PATIENT Detector

  44. CT DETECTORS

  45. DETECTOR TYPES: SCINTILLATION S. CRYSTAL S. CRYSTAL PHOTODIODE PM TUBE

  46. SCINTILLATION CRYSTALS USED WITH PM TUBES: • SODIUM IODIDE –AFTERGLOW + LOW DYNAMIC RANGE ( USED IN THE PAST) • CALCIUM FLUORIDE • BISMUTH GERMANATE

  47. S. CRYSTAL USED WITH PHOTODIODE • CALCIUM TUNGSTATE • RARE EARTH OXIDES - CERAMIC

  48. DETECTOR TYPE: GAS IONIZATION XENON GAS 30 ATM

  49. EFFICIENCY OF DETECTORS- QDE • SCINTILLATION – 95% - 100%- COMMONLY USED IN III & IV GENERATION SCANNERS • GAS – 50% - 60%

  50. COMPUTER SYSTEM • RECONSTRUCTION AND POSTPROCESSING • CONTROL OF ALL SCANNER COMPONENTS • CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. • DATA FLOW DIRECTION

More Related