computed tomography instrumentation and operation dr. halima hawesa lecture 3-rad 466
TRANSCRIPT
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COMPUTED TOMOGRAPHYCOMPUTED TOMOGRAPHY INSTRUMENTATION AND INSTRUMENTATION AND
OPERATIONOPERATION
Dr. Halima HawesaLecture 3-RAD 466
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OUTLINEOUTLINE CT SYSTEM COMPONENTS – DEFINITION OF CT SYSTEM COMPONENTS – DEFINITION OF
A SCANNER A SCANNER SCANNER COORDINATE SYSTEM – XYZ, SCANNER COORDINATE SYSTEM – XYZ,
ISOCENTERISOCENTER IMAGING SYSTEMIMAGING SYSTEM COMPUTER SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, AND STORAGE DISPLAY, RECORDING, AND STORAGE
SYSTEMSSYSTEMS
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CT MAIN SYSTEMS
IMAGING SYSTEMIMAGING SYSTEM COMPUTER SYSTEMCOMPUTER SYSTEM DISPLAY, RECORDING, STORAGE DISPLAY, RECORDING, STORAGE
SYSTEMSYSTEM DATA ACQUISITION SYSTEMDATA ACQUISITION SYSTEM
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CT SYSTEMCT SYSTEMGANTRY
DETECTORS
S/H
ADC
ARRAY PROCESSOR
HOST COMPUTER
STORAGECONSOLE
SCAN CONTROLLER
DAC
GANTRY CONTROL
HIGH VOLTAGE GENERATOR
X-RAY TUBE
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SCANNERSCANNER
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SCANNER
GANTRYGANTRY PATIENT COUCHPATIENT COUCH
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GANTRY HOUSES:GANTRY HOUSES:
X-RAY TUBEX-RAY TUBE GENERATOR (LOW VOLTAGE DESIGN)GENERATOR (LOW VOLTAGE DESIGN) COLLIMATORSCOLLIMATORS DETECTORSDETECTORS
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GANTRY CHARACTERISTICS
APERTUREAPERTURE TILTING RANGETILTING RANGE
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MOST OF THE SCANNERS MOST OF THE SCANNERS HAVE 70CM APERTUREHAVE 70CM APERTURE
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70 CM
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COORDINATE SYSTEMCOORDINATE SYSTEM
X
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COORDINATE SYSTEMCOORDINATE SYSTEM
Y
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COORDINATE SYSTEMCOORDINATE SYSTEM
Z
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ISOCENTERISOCENTER
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TILTING RANGE OF MOST TILTING RANGE OF MOST SCANNERS- +30 TO -30 SCANNERS- +30 TO -30
DEGREESDEGREES
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PATIENT COUCH :PATIENT COUCH :
450 LBS (204 KG) 450 LBS (204 KG) DISTRIBUTED WEIGHT LIMITDISTRIBUTED WEIGHT LIMIT
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SCANNABLE RANGE:SCANNABLE RANGE:
COVERAGE FROM HEAD TO COVERAGE FROM HEAD TO THIGH (162CM) THIGH (162CM)
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MAX. SCANNABLE RANGEMAX. SCANNABLE RANGE
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IMAGING SYSTEMIMAGING SYSTEM
PRODUCTION OF X-RAYSPRODUCTION OF X-RAYS SHAPING OF X-RAY BEAM ENERGYSHAPING OF X-RAY BEAM ENERGY FILTERING X-RAY BEAMFILTERING X-RAY BEAM
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IMAGING SYSTEM COMPONENTS
X-RAY TUBEX-RAY TUBE GENERATOR –GENERATOR –HIGH VOLTAGEHIGH VOLTAGE COLLIMATORSCOLLIMATORS FILTER FILTER DETECTORSDETECTORS DETECTOR ELECTRONICSDETECTOR ELECTRONICS
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X-RAY TUBE AND X-RAY X-RAY TUBE AND X-RAY PRODUCTIONPRODUCTION
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CATHODE --------CATHODE --------MADE OF TUNGSTENMADE OF TUNGSTEN
IN CT – STILL SMALL AND LARGE
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THERMIONIC EMISSIONTHERMIONIC 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 FOCAL SPOT- CT UTILIZES DIFFERENT FOCAL SPOTS DIFFERENT FOCAL SPOTS
THE FILAMENT SIZE – LENGTH – THE FILAMENT SIZE – LENGTH – FOCAL SPOTFOCAL SPOT
SMALLER FOCAL SPOT - Low mA
SMALLER FOCAL SPOT – sharper image
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ANODE +++++ MADE OF ANODE +++++ MADE OF TUNGSTEN AND TUNGSTEN AND MOLYBDENUMMOLYBDENUM
TUNGSTENTARGET
TARGET MADE OF TUNGSTEN AND
RHENIUM
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mA – tube currentmA – tube current
The number of electrons flowing from The number of electrons flowing from cathode to anodecathode to anode
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kVpkVp
Potential difference between cathode Potential difference between cathode and anode (Volts) kilo means 1,000 and anode (Volts) kilo means 1,000 x.x.
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S –time of exposureS –time of exposure
mAs tube current for mAs tube current for certain length of timecertain length of time
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X-RAY PRODUCTION RESULTS X-RAY PRODUCTION RESULTS IN A LOT OF HEAT AND VERY IN A LOT OF HEAT AND VERY
LITTLE LITTLE X-RAYS BEING GENERATEDX-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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REDUCTION OF HEAT UNITS – REDUCTION OF HEAT UNITS – TECHNIQUE COMPENSATIONTECHNIQUE COMPENSATION
kVp kVp
mAmA
TimeTime
INCREASED NOISE
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TOO LOW OF kVp:TOO LOW OF kVp:
NOISE !!!!NOISE !!!!
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Why changingWhy changing mA or time mA or time
Avoiding motion – mA timeAvoiding motion – mA time Pediatric technique modificationPediatric technique modification Reducing noise - mAsReducing noise - mAs
NOISE MOTION
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Tube voltage (kVp) CHANGETube voltage (kVp) CHANGE
kVp
INTENSITY -
ENERGY –
15% INCREASE OF KVP = 2 * mAs
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kVp IN CTkVp IN CT
80-14080-140 TOO LOW – NOISE TOO LOW – NOISE
(NOT ENOUGH PENETRATION OF THE PATIENT )(NOT ENOUGH PENETRATION OF THE PATIENT )
PHOTON STARVATION - NOISE!!!!!PHOTON STARVATION - NOISE!!!!!
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HIGH VOLTAGE GENERATOR HIGH VOLTAGE GENERATOR –(HVG)–(HVG)
GENERATES HIGH VOLTAGE GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBEANODE OF AN X-RAY TUBE
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CT GENERATOR
5-50 kHz5-50 kHz 30-60 kW30-60 kW
KVP SELECTION:
80, 100, 120, 130,140
mA selection:
30, 50, 65, 100, 125, 150, 175, 200, 400
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Filter
Patient
DEFINES SLICE THICKNESS
REDUCES SCATTER RECHING THE PATIENT
Detector
CT Imaging Steps
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COLLIMATION IN CTCOLLIMATION IN CTBASIC DATA AQUSITION SCHEME IN CTBASIC DATA AQUSITION SCHEME IN CT
ADC
PRE-PATIENT COLLIMATION
POST-PATIENT COLLIMATION
FILTRATION
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X-RAY EMISSIONX-RAY EMISSIONTUBE CURRENT CHANGETUBE CURRENT CHANGE
CURRENTINTENSITY
ENERGY – NO CHANGE
2 * mA = 2 * number of photons4 * mA = 4 * number of photons
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FILTRATION CHANGEFILTRATION CHANGE
FILTRATION
INTENSITY
ENERGY
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FILTRATION MATERIALFILTRATION MATERIAL
ALUMINIUM ( SPECIAL FILTER IN CT)ALUMINIUM ( SPECIAL FILTER IN CT)
TO MAKE THE BEAM HARDER AND MORE MONOENERGETIC
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CT DETECTORSCT DETECTORS
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DETECTOR TYPES: DETECTOR TYPES: SCINTILLATIONSCINTILLATION
PM TUBE
S. CRYSTALS. CRYSTAL
PHOTODIODE
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SCINTILLATION CRYSTALS SCINTILLATION CRYSTALS USED WITH PM TUBES:USED WITH PM TUBES:
SODIUM IODIDE SODIUM IODIDE CALCIUM FLUORIDECALCIUM FLUORIDE
BISMUTH GERMANATEBISMUTH GERMANATE
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S. CRYSTAL USED WITH S. CRYSTAL USED WITH PHOTODIODEPHOTODIODE
CALCIUM TUNGSTATECALCIUM TUNGSTATE RARE EARTH OXIDES - CERAMICRARE EARTH OXIDES - CERAMIC
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DETECTOR TYPE: GAS IONIZATIONDETECTOR TYPE: GAS IONIZATION
XENON GAS
30 ATM
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EFFICIENCY OF DETECTORS- EFFICIENCY OF DETECTORS- QDEQDE
SCINTILLATION – 95% - 100%- SCINTILLATION – 95% - 100%- COMMONLY USED IN III & IV COMMONLY USED IN III & IV GENERATION SCANNERSGENERATION SCANNERS
GAS – 50% - 60%GAS – 50% - 60%
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COMPUTER SYSTEMCOMPUTER SYSTEM
RECONSTRUCTION AND RECONSTRUCTION AND POSTPROCESSINGPOSTPROCESSING
CONTROL OF ALL SCANNER CONTROL OF ALL SCANNER COMPONENTSCOMPONENTS
CONTROL OF DATA ACQUSITION, CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY.PROCESSING, DISPLAY.
DATA FLOW DIRECTION DATA FLOW DIRECTION
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COMPUTER SYSTEM IN CTCOMPUTER SYSTEM IN CT
MINICOMPUTERSMINICOMPUTERS
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COMPUTER SYSTEM COMPUTER SYSTEM COMPOSED OF:COMPOSED OF:
HARDWAREHARDWARE SOFTWARESOFTWARE
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COMPUTER PROCESSING IN COMPUTER PROCESSING IN CTCT
SEQUENTIAL PROCESSINGSEQUENTIAL PROCESSING MULTITASKINGMULTITASKING MULTIPROCESSINGMULTIPROCESSING
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SOFTWARE –PROGRAM (S) SOFTWARE –PROGRAM (S) HELPING CT USER TO HELPING CT USER TO
COMMUNICATE WITH THE COMMUNICATE WITH THE CT SYSTEMCT SYSTEM
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CT OPERATING SYSTEM-CT OPERATING SYSTEM-PROGRAMS THAT CONTROL PROGRAMS THAT CONTROL
THE HARDWARE THE HARDWARE COMPONENTS AND THE COMPONENTS AND THE OVERALL OPERATION OF OVERALL OPERATION OF
THE CT COMPUTERTHE CT COMPUTER
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CT OPERATING SYSTEMCT OPERATING SYSTEM
UNIXUNIX WINDOWSWINDOWS
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HOST COMPUTER
CONTROL OF ALL COMPONENTSCONTROL OF ALL COMPONENTS CONTROL OF DATA ACQUSITION, CONTROL OF DATA ACQUSITION,
PROCESSING, DISPLAY.PROCESSING, DISPLAY. DATA FLOW DIRECTION DATA FLOW DIRECTION
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ARRAY PROCESSORARRAY PROCESSOR
TAKES DETECTOR MEASUREMENTS TAKES DETECTOR MEASUREMENTS FORM HUNDREDS OF PROJECTIONS. FORM HUNDREDS OF PROJECTIONS. RESPONSIBLE FOR RETROSPECTIVE RESPONSIBLE FOR RETROSPECTIVE RECONSTRUCTION AND RECONSTRUCTION AND POSTPROCESSING OF DATA. POSTPROCESSING OF DATA.
THE MORE PROCESSORS IN THE COMPUTER THE SHORTER THE RECONSTRUCTION TIME
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DATA ACQUISITION SYSTEM DATA ACQUISITION SYSTEM (DAS)(DAS)
SET OF ELECTRONICS BETWEEN SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER. DETECTORS AND HOST COMPUTER.
IT CONTAINS: AMPLIFIER, ADC, DAC, IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H. GENERATOR, S/H.
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AMPLIFIERAMPLIFIER
SIGNAL FROM DETECTORS GOES TO SIGNAL FROM DETECTORS GOES TO AMPLIFIERS FOR SIGNAL AMPLIFIERS FOR SIGNAL MAGNIFICATION AND THEN IS SENT MAGNIFICATION AND THEN IS SENT TO SAMPLE/HOLD UNITTO SAMPLE/HOLD UNIT
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ADCADC
CONVERTS ANALOG SIGNAL OUTPUT CONVERTS ANALOG SIGNAL OUTPUT FROM THE SCANNING EQUIPMENT TO FROM THE SCANNING EQUIPMENT TO A DIGITAL SIGNAL SO IT CAN BE A DIGITAL SIGNAL SO IT CAN BE PROCESSED BY A COMPUTER.PROCESSED BY A COMPUTER.
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SAMPLE/HOLD UNIT (S/H)SAMPLE/HOLD UNIT (S/H)
LOCATED BETWEEN LOCATED BETWEEN AMPLIFIERAMPLIFIER AND AND ADC ADC PERFORMS SAMPLING AND ASSIGNS PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO DIGITAL MATRIX CORRESPONDING TO THE STRUCTURESTHE STRUCTURES
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DASDASGANTRY
DETECTORS
S/H
ADC
ARRAY PROCESSOR
HOST COMPUTER
STORAGECONSOLE
SCAN CONTROLLER
DAC
GANTRY CONTROL
HIGH VOLTAGE GENERATOR
X-RAY TUBE
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IMAGE DISPLAY, RECORDING, STORAGE
DISPLAYS IMAGE ( OUTPUT FROM DISPLAYS IMAGE ( OUTPUT FROM COMPUTER)COMPUTER)
PROVIDES HARD COPY OF THE IMAGEPROVIDES HARD COPY OF THE IMAGE FACILITATES THE STORAGE AND FACILITATES THE STORAGE AND
RETRIEVAL OF DIGITAL DATARETRIEVAL OF DIGITAL DATA COMMUNICATES IMAGES IN THE COMMUNICATES IMAGES IN THE
NETWORKNETWORK
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IMAGE IMAGE DISPLAYDISPLAY
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IMAGE RECORDING SYSTEMSIMAGE RECORDING SYSTEMS(LASER PRINTERS)(LASER PRINTERS)
SOLID STATE SOLID STATE LASER PRINTERSLASER PRINTERS
GAS LASER GAS LASER PRINTERSPRINTERS
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HARD COPYHARD COPY
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IMAGE STORAGE MEDIAIMAGE STORAGE MEDIA
MAGNETIC TAPESMAGNETIC TAPES MAGNETO-OPTICAL DISK (MOD)MAGNETO-OPTICAL DISK (MOD) CDCD
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COMMUNICATIONCOMMUNICATION
PACSPACS
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OVERREAD NETWORKOVERREAD NETWORK While most teleradiology systems purchased over While most teleradiology systems purchased over
the last decade were intended for on-call the last decade were intended for on-call purposes, the past two years have seen a rapid purposes, the past two years have seen a rapid
increase in the use of teleradiology to link increase in the use of teleradiology to link hospitals and affiliated satellite facilities, other hospitals and affiliated satellite facilities, other
primary hospitals, and imaging centers. A number primary hospitals, and imaging centers. A number of the enabling technologies needed for effective of the enabling technologies needed for effective overread networks, such as more affordable high-overread networks, such as more affordable high-
speed telecommunications networks and speed telecommunications networks and improved data compression techniques, have improved data compression techniques, have
matured in recent yearsmatured in recent years..
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CT ROOM LAYOUTCT ROOM LAYOUT
Thanks for listening