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COMPUTED TOMOGRAPHY INSTRUMENTATION AND
OPERATION
Nchanji NKEH [email protected]/[email protected]
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
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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CT MAIN SYSTEMS
IMAGING SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, STORAGE SYSTEM DATA ACQUISITION SYSTEM
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CT SYSTEMGANTRY
DETECTORS
SAMPLE HOLD UNIT
ADC
ARRAY PROCESSOR
HOST COMPUTER
STORAGECONSOLE
SCAN CONTROLLER
DAC
GANTRY CONTROL
HIGH VOLTAGE GENERATOR
X-RAY TUBE18
IMAGING SYSTEM COMPONENTS
X-RAY TUBE GENERATOR –HIGH VOLTAGEHIGH VOLTAGE COLLIMATORS FILTER DETECTORS DETECTOR ELECTRONICS
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THERMIONIC EMISSION
CATHODE HEATED UP TO AT LEAST 2,200 DEG. CELSIUS TO LIBERATE ELECTRONS FOR TRANSIT TO ANODE
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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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X-RAY PRODUCTION RESULTS IN A LOT OF HEAT AND VERY LITTLE X-RAYS BEING GENERATEDHEAT UNITS CALCULATION
HU= kVp X mA x time
MOST CT TUBES HEAT CAPACITY 3-5 MILLION HU
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TUBE CURRENT CHANGE
CURRENTINTENSITY
ENERGY – NO CHANGE
2 * mA = 2 * number of photons4 * mA = 4 * number of photons
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Why changing mA or time Avoiding motion – mA time Pediatric technique modification Reducing noise - mAs
NOISE MOTION
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kVp IN CT 80-140 TOO LOW – NOISE (NOT ENOUGH PENETRATION OF THE PATIENT ) PHOTON STARVATION - NOISE!!!!!PHOTON STARVATION - NOISE!!!!!
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HIGH VOLTAGE GENERATOR –(HVG)
GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBE
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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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FILTRATION MATERIAL ALUMINIUM ( SPECIAL FILTER IN CT)
BOWTIE
TO MAKE THE BEAM HARDER AND MORE MONOENERGETIC
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SCINTILLATION CRYSTALS USED WITH PM TUBES: SODIUM IODIDE –AFTERGLOW + LOW DYNAMIC AFTERGLOW + LOW DYNAMIC
RANGE RANGE ( USED IN THE PAST)( USED IN THE PAST)
CALCIUM FLUORIDE
BISMUTH GERMANATE
67
EFFICIENCY OF DETECTORS- QDE
SCINTILLATION – 95% - 100%- COMMONLY COMMONLY USED IN III & IV GENERATION SCANNERSUSED IN III & IV GENERATION SCANNERS
GAS – 50% - 60%
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COMPUTER SYSTEM
RECONSTRUCTION AND POSTPROCESSING CONTROL OF ALL SCANNER COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING,
DISPLAY. DATA FLOW DIRECTION
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CT OPERATING SYSTEM-PROGRAMS THAT CONTROL THE HARDWARE COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER
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HOST COMPUTER
CONTROL OF ALL COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING,
DISPLAY. DATA FLOW DIRECTION
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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
79
DATA ACQUISITION SYSTEM (DAS)
SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.
IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H.
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AMPLIFIER
SIGNAL FROM DETECTORS GOES TO AMPLIFIERS FOR SIGNAL MAGNIFICATION AND THEN IS SENT TO SAMPLE/HOLD UNIT
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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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SAMPLE/HOLD UNIT (S/H)
LOCATED BETWEEN AMPLIFIERAMPLIFIER AND ADC ADC PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO THE STRUCTURES
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DASGANTRY
DETECTORS
S/H
ADC
ARRAY PROCESSOR
HOST COMPUTER
STORAGECONSOLE
SCAN CONTROLLER
DAC
GANTRY CONTROL
HIGH VOLTAGE GENERATOR
X-RAY TUBE84
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
85
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.
91
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.
92
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
95
NEXT LECTURE:
1. ULTRASONOGRAPHIC INSTRUMENTATION
2. MAMMORAPHIC INSTRUMENTATION
3. FLUOROSCOPIC INSTRUMENTATION
4. MRI INSTRUMENTATION
99