EASY TO GRASP, FULL OF VITAL FACTS, RECOMMENDED FOR UNDERGRADUATE MEDICAL IMAGING TRAINING. VERY HELPFUL

1. COMPUTED TOMOGRAPHY
INSTRUMENTATION AND
OPERATION
Nchanji NKEH Kenneth
kennchanji@yahoo.com/nkeh92@gmail.com
671459765/662695118
B.TECH/HPD, MDIRT
CHM Virtued Academy India (Ongoing)
Leader
Radiology Department
Level 300 MDI
2016/2017 Academic Year
ST. Louis UNIHEBS mile 3 Nkwen ,Bamenda- Cameroon
1

2. COMPUTED TOMOGRAPHY
INSTRUMENTATION AND OPERATION
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15. 15

16. OUTLINE
 CT SYSTEM COMPONENTS – DEFINITION OF A
SCANNER
 SCANNER COORDINATE SYSTEM – XYZ,
ISOCENTER
 IMAGING SYSTEM
 COMPUTER SYSTEM
 DISPLAY, RECORDING, AND STORAGE
SYSTEMS
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17. CT MAIN SYSTEMS
 IMAGING SYSTEM
 COMPUTER SYSTEM
 DISPLAY, RECORDING, STORAGE SYSTEM
 DATA ACQUISITION SYSTEM
17

18. CT SYSTEM
GANTRY
DETECTORS
SAMPLE HOLD UNIT
ADC
ARRAY PROCESSOR
HOST
COMPUTER
STORAGE
CONSOLE
SCAN CONTROLLER
DAC
GANTRY CONTROL
HIGH VOLTAGE
GENERATOR
X-RAY TUBE
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19. SCANNER 19

20. Some CT hardware 20

21. SCANNER
 GANTRY
 PATIENT COUCH
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23. 23

24. 24

25. GANTRY HOUSES:
 X-RAY TUBE
 GENERATOR (LOW VOLTAGE DESIGN)
 COLLIMATORS
 DETECTORS
25

26. GANTRY
CHARACTERISTICS
 APERTURE
 TILTING RANGE
26

27. MOST OF THE SCANNERS HAVE
70CM APERTURE
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28. 70 CM
28

29. COORDINATE SYSTEM
X
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30. COORDINATE SYSTEM
Y
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31. COORDINATE SYSTEM
Z
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32. ISOCENTER 32

33. TILTING RANGE OF MOST
SCANNERS- +30 TO -30
DEGREES
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34. PATIENT COUCH :
450 LBS (204 KG) DISTRIBUTED
WEIGHT LIMIT
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35. SCANNABLE RANGE:
COVERAGE FROM HEAD TO
THIGH (162CM)
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36. MAX. SCANNABLE RANGE 36

37. IMAGING SYSTEM
 PRODUCTION OF X-RAYS
 SHAPING OF X-RAY BEAM ENERGY
 FILTERING X-RAY BEAM
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38. IMAGING SYSTEM
COMPONENTS
 X-RAY TUBE
 GENERATOR –HIGH VOLTAGEHIGH VOLTAGE
 COLLIMATORS
 FILTER
 DETECTORS
 DETECTOR ELECTRONICS
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39. X-RAY TUBE AND X-RAY
PRODUCTION
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40. 40

41. CATHODE --------
MADE OF TUNGSTEN
IN CT – STILL SMALL AND LARGE
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42. THERMIONIC EMISSION
CATHODE HEATED UP TO AT LEAST 2,200 DEG. CELSIUS
TO LIBERATE ELECTRONS FOR TRANSIT TO ANODE
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43. FOCAL SPOT- CT UTILIZES
DIFFERENT FOCAL SPOTS
 THE FILAMENT SIZE – LENGTH – FOCAL SPOTFOCAL SPOT
SMALLER FOCAL SPOT - Low mA
SMALLER FOCAL SPOT – sharper image
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44. ANODE +++++ MADE OF
TUNGSTEN AND
MOLYBDENUM
TUNGSTEN
TARGET
TARGET MADE OF TUNGSTEN
AND
RHENIUM
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45. mA – tube current
 The number of electrons flowing from cathode to
anode
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46. kVp
 Potential difference between cathode and
anode (Volts) kilo means 1,000 x.
46

47. S –time of exposure
mAs tube current for certain
length of time
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48. 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
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49. REDUCTION OF HEAT UNITS –
TECHNIQUE
COMPENSATION kVp
 mA
 Time
INCREASED NOISE
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50. TOO LOW OF kVp:
 NOISE !!!!NOISE !!!!
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51. X-RAY EMISSION 51

52. TUBE CURRENT CHANGE
CURRENT
INTENSITY
ENERGY – NO CHANGE
2 * mA = 2 * number of photons
4 * mA = 4 * number of photons
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53. Why changing
mA or time
 Avoiding motion – mA time
 Pediatric technique modification
 Reducing noise - mAs
NOISE
MOTION
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54. Tube voltage (kVp)
CHANGE
kVp
INTENSITY -
ENERGY –
15% INCREASE OF KVP = 2 * mAs
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55. kVp IN CT
 80-140
 TOO LOW – NOISE
(NOT ENOUGH PENETRATION OF THE PATIENT )
PHOTON STARVATION - NOISE!!!!!PHOTON STARVATION - NOISE!!!!!
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56. HIGH VOLTAGE
GENERATOR –(HVG)
 GENERATES HIGH VOLTAGE POTENTIAL BETWEEN
CATHODE AND ANODE OF AN X-RAY TUBE
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57. 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
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58. COLLIMATION IN CT
ADC
PRE-PATIENT COLLIMATION
POST-PATIENT COLLIMATION
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59. BASIC DATA AQUSITION SCHEME IN CT
ADC
FILTRATION
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60. FILTRATION CHANGE
FILTRATION
INTENSITY
ENERGY –
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61. FILTRATION MATERIAL
 ALUMINIUM ( SPECIAL FILTER IN CT)
BOWTIE
TO MAKE THE BEAM HARDER AND
MORE MONOENERGETIC
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62. Filter
Patient
DEFINES SLICE
THICKNESS
REDUCES SCATTER
RECHING THE PATIENT
Detector
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63. CT DETECTORS 63

64. CONCEPT OF MDCT 64

65. SDTCT AND MDCT 65

66. DETECTOR TYPES: SCINTILLATION
PM TUBE
S. CRYSTAL
S. CRYSTAL
PHOTODIODE
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67. SCINTILLATION CRYSTALS
USED WITH PM TUBES:
 SODIUM IODIDE –AFTERGLOW + LOW DYNAMICAFTERGLOW + LOW DYNAMIC
RANGERANGE ( USED IN THE PAST)( USED IN THE PAST)
 CALCIUM FLUORIDE
 BISMUTH GERMANATE
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68. S. CRYSTAL USED WITH
PHOTODIODE
 CALCIUM TUNGSTATE
 RARE EARTH OXIDES - CERAMIC
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69. DETECTOR TYPE: GAS IONIZATION
XENON GAS
30 ATM
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70. EFFICIENCY OF
DETECTORS- QDE
 SCINTILLATION – 95% - 100%- COMMONLY USED INCOMMONLY USED IN
III & IV GENERATION SCANNERSIII & IV GENERATION SCANNERS
 GAS – 50% - 60%
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71. COMPUTER SYSTEM
 RECONSTRUCTION AND POSTPROCESSING
 CONTROL OF ALL SCANNER COMPONENTS
 CONTROL OF DATA ACQUSITION, PROCESSING,
DISPLAY.
 DATA FLOW DIRECTION
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72. COMPUTER SYSTEM IN CT
 MINICOMPUTERS
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73. COMPUTER SYSTEM
COMPOSED OF:
 HARDWARE
 SOFTWARE
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74. COMPUTER PROCESSING
IN CT
 SEQUENTIAL PROCESSING
 MULTITASKING
 MULTIPROCESSING
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75. SOFTWARE –PROGRAM (S)
HELPING CT USER TO
COMMUNICATE WITH THE CT
SYSTEM
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76. CT OPERATING SYSTEM-
PROGRAMS THAT CONTROL
THE HARDWARE COMPONENTS
AND THE OVERALL OPERATION
OF THE CT COMPUTER
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77. CT OPERATING SYSTEM
 UNIX
 WINDOWS
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78. HOST COMPUTER
 CONTROL OF ALL COMPONENTS
 CONTROL OF DATA ACQUSITION, PROCESSING,
DISPLAY.
 DATA FLOW DIRECTION
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79. ARRAY PROCESSOR
 TAKES DETECTOR MEASUREMENTS FROM HUNDREDS OF
PROJECTIONS. RESPONSIBLE FOR RETROSPECTIVE
RECONSTRUCTION AND POSTPROCESSING OF DATA.
THE MORE PROCESSORS IN THE COMPUTER
THE SHORTER THE RECONSTRUCTION TIME
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80. DATA ACQUISITION
SYSTEM (DAS)
 SET OF ELECTRONICS BETWEEN DETECTORS AND
HOST COMPUTER.
 IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR,
S/H.
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81. AMPLIFIER
 SIGNAL FROM DETECTORS GOES TO AMPLIFIERS
FOR SIGNAL MAGNIFICATION AND THEN IS SENT
TO SAMPLE/HOLD UNIT
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82. ADC
 CONVERTS ANALOG SIGNAL OUTPUT FROM THE
SCANNING EQUIPMENT TO A DIGITAL SIGNAL SO IT
CAN BE PROCESSED BY A COMPUTER.
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83. SAMPLE/HOLD UNIT (S/H)
 LOCATED BETWEEN AMPLIFIERAMPLIFIER AND ADCADC PERFORMS SAMPLING
AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL
MATRIX CORRESPONDING TO THE STRUCTURES
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84. DAS
GANTRY
DETECTORS
S/H
ADC
ARRAY PROCESSOR
HOST
COMPUTER
STORAGE
CONSOLE
SCAN CONTROLLER
DAC
GANTRY CONTROL
HIGH VOLTAGE
GENERATOR
X-RAY TUBE
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85. 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
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86. IMAGE
DISPLAY
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87. IMAGE RECORDING SYSTEMS
(LASER PRINTERS)
 SOLID STATE LASER
PRINTERS
 GAS LASER PRINTERS
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88. HARD COPY 88

89. IMAGE STORAGE MEDIA
 MAGNETIC TAPES
 MAGNETO-OPTICAL DISK (MOD)
 CD
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90. COMMUNICATION
 PACS
90

91. 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.
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92. NightHawk Radiology Services has developed
an innovative approach to the delivery of
radiology services by operating centralized,
state-of-the-art reading centers in Sydney,
Australia and Zurich, Switzerland. Staffing
U.S.-trained, board-certified radiologists
specializing in emergency radiology, these
locations are ideally situated for U.S. care
because when it’s the middle of the night in
Boston, it’s daytime “Down Under.” When it’s
early morning in Los Angeles, it’s daytime in
the Alps. From the centralized reading centers,
NightHawk radiologists interpret exams and
report the results to attending physicians in
real-time, usually less than 20 minutes.
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93. CT ROOM LAYOUT 93

94. How much does a CT
scanner cost?
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95. How much ??
4-slice scanner: $85,000 - $115,000
16-slice scanner: $145,000 - $225,000
64-slice scanner: $250,000 - $450,000
Service contracts: $100,000 - $135,000
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97. 97

98. Lecture delivered with use of
resources from ICRP, IAEA,
AAPM and GE
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99. NEXT LECTURE:
1. ULTRASONOGRAPHIC INSTRUMENTATION
2. MAMMORAPHIC INSTRUMENTATION
3. FLUOROSCOPIC INSTRUMENTATION
4. MRI INSTRUMENTATION
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