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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
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COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION
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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
SCANNER 19
Some CT hardware 20
SCANNER
GANTRY PATIENT COUCH
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GANTRY HOUSES:
X-RAY TUBE GENERATOR (LOW VOLTAGE DESIGN) COLLIMATORS DETECTORS
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GANTRY CHARACTERISTICS
APERTURE TILTING RANGE
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MOST OF THE SCANNERS HAVE 70CM APERTURE
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70 CM
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COORDINATE SYSTEM
X
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COORDINATE SYSTEM
Y
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COORDINATE SYSTEM
Z
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ISOCENTER 32
TILTING RANGE OF MOST SCANNERS- +30 TO -30
DEGREES
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PATIENT COUCH :
450 LBS (204 KG) DISTRIBUTED WEIGHT LIMIT
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SCANNABLE RANGE:
COVERAGE FROM HEAD TO THIGH (162CM)
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MAX. SCANNABLE RANGE 36
IMAGING SYSTEM
PRODUCTION OF X-RAYS SHAPING OF X-RAY BEAM ENERGY FILTERING X-RAY BEAM
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IMAGING SYSTEM COMPONENTS
X-RAY TUBE GENERATOR –HIGH VOLTAGEHIGH VOLTAGE COLLIMATORS FILTER DETECTORS DETECTOR ELECTRONICS
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X-RAY TUBE AND X-RAY PRODUCTION
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CATHODE --------MADE OF TUNGSTEN
IN CT – STILL SMALL AND LARGE
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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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ANODE +++++ MADE OF TUNGSTEN AND MOLYBDENUM
TUNGSTENTARGET
TARGET MADE OF TUNGSTEN AND
RHENIUM
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mA – tube current
The number of electrons flowing from cathode to anode
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kVp
Potential difference between cathode and anode (Volts) kilo means 1,000 x.
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S –time of exposure
mAs tube current for certain length of time
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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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REDUCTION OF HEAT UNITS – TECHNIQUE COMPENSATION kVp
mA
Time
INCREASED NOISE
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TOO LOW OF kVp:
NOISE !!!!NOISE !!!!
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X-RAY EMISSION 51
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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Tube voltage (kVp) CHANGE
kVp
INTENSITY -
ENERGY –
15% INCREASE OF KVP = 2 * mAs
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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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COLLIMATION IN CT
ADC
PRE-PATIENT COLLIMATION
POST-PATIENT COLLIMATION
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BASIC DATA AQUSITION SCHEME IN CT
ADC
FILTRATION
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FILTRATION CHANGE
FILTRATION
INTENSITY
ENERGY –
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FILTRATION MATERIAL ALUMINIUM ( SPECIAL FILTER IN CT)
BOWTIE
TO MAKE THE BEAM HARDER AND MORE MONOENERGETIC
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Filter
Patient
DEFINES SLICE THICKNESS
REDUCES SCATTER RECHING THE PATIENT
Detector
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CT DETECTORS 63
CONCEPT OF MDCT 64
SDTCT AND MDCT 65
DETECTOR TYPES: SCINTILLATION
PM TUBE
S. CRYSTALS. CRYSTAL
PHOTODIODE
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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
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S. CRYSTAL USED WITH PHOTODIODE
CALCIUM TUNGSTATE RARE EARTH OXIDES - CERAMIC
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DETECTOR TYPE: GAS IONIZATION
XENON GAS
30 ATM
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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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COMPUTER SYSTEM IN CT
MINICOMPUTERS
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COMPUTER SYSTEM COMPOSED OF:
HARDWARE SOFTWARE
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COMPUTER PROCESSING IN CT
SEQUENTIAL PROCESSING MULTITASKING MULTIPROCESSING
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SOFTWARE –PROGRAM (S) HELPING CT USER TO COMMUNICATE WITH THE CT SYSTEM
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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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CT OPERATING SYSTEM
UNIX WINDOWS
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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
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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
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IMAGE DISPLAY
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IMAGE RECORDING SYSTEMS(LASER PRINTERS) SOLID STATE
LASER PRINTERS GAS LASER
PRINTERS
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HARD COPY 88
IMAGE STORAGE MEDIA
MAGNETIC TAPES MAGNETO-OPTICAL DISK (MOD) CD
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COMMUNICATION
PACS
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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.
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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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CT ROOM LAYOUT 93
How much does a CT scanner cost?
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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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Lecture delivered with use of resources from ICRP, IAEA,
AAPM and GE
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NEXT LECTURE:
1. ULTRASONOGRAPHIC INSTRUMENTATION
2. MAMMORAPHIC INSTRUMENTATION
3. FLUOROSCOPIC INSTRUMENTATION
4. MRI INSTRUMENTATION
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