1. COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION
Dr. Halima Hawesa
Lecture 3-RAD 466

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

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

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

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

36. 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

37. CT Imaging Steps Filter Patient Detector DEFINES SLICE THICKNESS
REDUCES SCATTER
RECHING THE PATIENT
Detector

38. COLLIMATION IN CT BASIC DATA AQUSITION SCHEME IN CT
FILTRATION
PRE-PATIENT COLLIMATION
POST-PATIENT COLLIMATION
ADC

39. X-RAY EMISSION TUBE CURRENT CHANGE
INTENSITY
ENERGY – NO CHANGE
CURRENT
2 * mA = 2 * number of photons
4 * mA = 4 * number of photons

40. FILTRATION CHANGE
INTENSITY
ENERGY
FILTRATION

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

42. CT DETECTORS

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

44. SCINTILLATION CRYSTALS USED WITH PM TUBES:
SODIUM IODIDE
CALCIUM FLUORIDE
BISMUTH GERMANATE

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

46. DETECTOR TYPE: GAS IONIZATION
XENON GAS
30 ATM

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

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

49. COMPUTER SYSTEM IN CT
MINICOMPUTERS

50. COMPUTER SYSTEM COMPOSED OF:
HARDWARE
SOFTWARE

51. COMPUTER PROCESSING IN CT
SEQUENTIAL PROCESSING
MULTITASKING
MULTIPROCESSING

52. SOFTWARE –PROGRAM (S) HELPING CT USER TO COMMUNICATE WITH THE CT SYSTEM

53. CT OPERATING SYSTEM-PROGRAMS THAT CONTROL THE HARDWARE COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

54. CT OPERATING SYSTEM
UNIX
WINDOWS

55. HOST COMPUTER CONTROL OF ALL COMPONENTS
CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY.
DATA FLOW DIRECTION

56. ARRAY PROCESSOR
TAKES DETECTOR MEASUREMENTS FORM HUNDREDS OF PROJECTIONS. RESPONSIBLE FOR RETROSPECTIVE RECONSTRUCTION AND POSTPROCESSING OF DATA.
THE MORE PROCESSORS IN THE COMPUTER
THE SHORTER THE RECONSTRUCTION TIME

57. DATA ACQUISITION SYSTEM (DAS)
SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.
IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H.

58. AMPLIFIER
SIGNAL FROM DETECTORS GOES TO AMPLIFIERS FOR SIGNAL MAGNIFICATION AND THEN IS SENT TO SAMPLE/HOLD UNIT

59. ADC
CONVERTS ANALOG SIGNAL OUTPUT FROM THE SCANNING EQUIPMENT TO A DIGITAL SIGNAL SO IT CAN BE PROCESSED BY A COMPUTER.

60. SAMPLE/HOLD UNIT (S/H)
LOCATED BETWEEN AMPLIFIER AND ADC PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO THE STRUCTURES

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

62. IMAGE DISPLAY, RECORDING, STORAGE
DISPLAYS IMAGE ( OUTPUT FROM COMPUTER)
PROVIDES HARD COPY OF THE IMAGE
FACILITATES THE STORAGE AND RETRIEVAL OF DIGITAL DATA
COMMUNICATES IMAGES IN THE NETWORK

63. IMAGE DISPLAY

64. IMAGE RECORDING SYSTEMS (LASER PRINTERS)
SOLID STATE LASER PRINTERS
GAS LASER PRINTERS

65. HARD COPY

66. IMAGE STORAGE MEDIA
MAGNETIC TAPES
MAGNETO-OPTICAL DISK (MOD) CD

67. COMMUNICATION
PACS

68. OVERREAD NETWORK
While most teleradiology systems purchased over the last decade were intended for on-call purposes, the past two years have seen a rapid increase in the use of teleradiology to link hospitals and affiliated satellite facilities, other primary hospitals, and imaging centers. A number of the enabling technologies needed for effective overread networks, such as more affordable high-speed telecommunications networks and improved data compression techniques, have matured in recent years.

69. CT ROOM LAYOUT
Thanks for listening