Transcript CT INSTRUMENTATION

COMPUTED TOMOGRAPHY
INSTRUMENTATION AND
OPERATION
OUTLINE
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CT SYSTEM COMPONENTS – DEFINITION OF A
SCANNER
SCANNER COORDINATE SYSTEM – XYZ,
ISOCENTER
IMAGING SYSTEM
COMPUTER SYSTEM
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DISPLAY, RECORDING, AND STORAGE SYSTEMS
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CT MAIN SYSTEMS
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IMAGING SYSTEM
COMPUTER SYSTEM
DISPLAY, RECORDING, STORAGE SYSTEM
DATA ACQUISITION SYSTEM
CT SYSTEM
GANTRY
X-RAY TUBE
GANTRY CONTROL
DETECTORS
S/H
ADC
DAC
HIGH VOLTAGE
GENERATOR
SCAN CONTROLLER
ARRAY PROCESSOR
HOST
COMPUTER
STORAGE
CONSOLE
SCANNER
SCANNER
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GANTRY
PATIENT COUCH
GANTRY HOUSES:
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X-RAY TUBE
GENERATOR (LOW VOLTAGE DESIGN)
COLLIMATORS
DETECTORS
GANTRY CHARACTERISTICS
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APERTURE
TILTING RANGE
MOST OF THE SCANNERS HAVE
70CM APERTURE
70 CM
COORDINATE SYSTEM
X
COORDINATE SYSTEM
Y
COORDINATE SYSTEM
Z
ISOCENTER
TILTING RANGE OF MOST
SCANNERS- +30 TO -30
DEGREES
PATIENT COUCH :
450 LBS (204 KG)
DISTRIBUTED WEIGHT LIMIT
SCANNABLE RANGE:
COVERAGE FROM HEAD TO
THIGH (162CM)
MAX. SCANNABLE RANGE
IMAGING SYSTEM
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PRODUCTION OF X-RAYS
SHAPING OF X-RAY BEAM ENERGY
FILTERING X-RAY BEAM
IMAGING SYSTEM COMPONENTS
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X-RAY TUBE
GENERATOR –HIGH VOLTAGE
COLLIMATORS
FILTER
DETECTORS
DETECTOR ELECTRONICS
X-RAY TUBE AND X-RAY
PRODUCTION
CATHODE -------MADE OF TUNGSTEN
IN CT – STILL SMALL AND LARGE
THERMIONIC EMISSION
CATHODE HEATED UP TO AT LEAST 2,200 DEG. CELSIUS
TO LIBERATE ELECTRONS FOR TRANSIT TO ANODE
FOCAL SPOT- CT UTILIZES
DIFFERENT FOCAL SPOTS
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THE FILAMENT SIZE – LENGTH – FOCAL SPOT
SMALLER FOCAL SPOT - Low mA
SMALLER FOCAL SPOT – sharper image
ANODE +++++ MADE OF
TUNGSTEN AND MOLYBDENUM
TUNGSTEN
TARGET
TARGET MADE OF TUNGSTEN
AND
RHENIUM
mA – tube current
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The number of electrons flowing from
cathode to anode
kVp
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Potential difference between cathode and
anode (Volts) kilo means 1,000 x.
S –time of exposure
mAs tube current for certain
length of time
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
REDUCTION OF HEAT UNITS –
TECHNIQUE COMPENSATION
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kVp
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mA
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Time
INCREASED NOISE
TOO LOW OF kVp:
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NOISE !!!!
X-RAY EMISSION
TUBE CURRENT CHANGE
INTENSITY
CURRENT
ENERGY – NO CHANGE
2 * mA = 2 * number of photons
4 * mA = 4 * number of photons
Why changing
mA or time
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Avoiding motion – mA
time
Pediatric technique modification
Reducing noise - mAs
NOISE
MOTION
Tube voltage (kVp) CHANGE
INTENSITY kVp
ENERGY –
15% INCREASE OF KVP = 2 * mAs
kVp IN CT
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80-140
TOO LOW – NOISE
(NOT ENOUGH PENETRATION OF THE PATIENT )
PHOTON STARVATION - NOISE!!!!!
HIGH VOLTAGE GENERATOR –
(HVG)
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GENERATES HIGH VOLTAGE POTENTIAL
BETWEEN CATHODE AND ANODE OF AN
X-RAY TUBE
CT GENERATOR
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5-50 kHz
30-60 kW
KVP SELECTION:
80, 100, 120, 130,140
mA selection:
30, 50, 65, 100, 125, 150, 175, 200, 400
COLLIMATION IN CT
PRE-PATIENT COLLIMATION
POST-PATIENT COLLIMATION
ADC
BASIC DATA AQUSITION SCHEME IN CT
FILTRATION
ADC
FILTRATION CHANGE
INTENSITY
FILTRATION
ENERGY –
FILTRATION MATERIAL
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ALUMINIUM ( SPECIAL FILTER IN CT)
BOWTIE
TO MAKE THE BEAM HARDER AND
MORE MONOENERGETIC
Filter
DEFINES SLICE
THICKNESS
Patient
REDUCES SCATTER
RECHING THE PATIENT
Detector
CT DETECTORS
DETECTOR TYPES: SCINTILLATION
S. CRYSTAL
S. CRYSTAL
PHOTODIODE
PM TUBE
SCINTILLATION CRYSTALS
USED WITH PM TUBES:
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SODIUM IODIDE –AFTERGLOW + LOW
DYNAMIC RANGE ( USED IN THE PAST)
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CALCIUM FLUORIDE
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BISMUTH GERMANATE
S. CRYSTAL USED WITH
PHOTODIODE
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CALCIUM TUNGSTATE
RARE EARTH OXIDES - CERAMIC
DETECTOR TYPE: GAS IONIZATION
XENON GAS
30 ATM
EFFICIENCY OF DETECTORSQDE
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SCINTILLATION – 95% - 100%COMMONLY USED IN III & IV
GENERATION SCANNERS
GAS – 50% - 60%
COMPUTER SYSTEM
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RECONSTRUCTION AND
POSTPROCESSING
CONTROL OF ALL SCANNER
COMPONENTS
CONTROL OF DATA ACQUSITION,
PROCESSING, DISPLAY.
DATA FLOW DIRECTION
COMPUTER SYSTEM IN CT
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MINICOMPUTERS
COMPUTER SYSTEM
COMPOSED OF:
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HARDWARE
SOFTWARE
COMPUTER PROCESSING IN CT
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SEQUENTIAL PROCESSING
MULTITASKING
MULTIPROCESSING
SOFTWARE –PROGRAM (S)
HELPING CT USER TO
COMMUNICATE WITH THE CT
SYSTEM
CT OPERATING SYSTEMPROGRAMS THAT CONTROL
THE HARDWARE COMPONENTS
AND THE OVERALL OPERATION
OF THE CT COMPUTER
CT OPERATING SYSTEM
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UNIX
WINDOWS
HOST COMPUTER
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CONTROL OF ALL COMPONENTS
CONTROL OF DATA ACQUSITION,
PROCESSING, DISPLAY.
DATA FLOW DIRECTION
ARRAY PROCESSOR
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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
DATA ACQUISITION SYSTEM
(DAS)
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SET OF ELECTRONICS BETWEEN
DETECTORS AND HOST COMPUTER.
IT CONTAINS: AMPLIFIER, ADC, DAC,
GENERATOR, S/H.
AMPLIFIER
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SIGNAL FROM DETECTORS GOES TO
AMPLIFIERS FOR SIGNAL
MAGNIFICATION AND THEN IS SENT TO
SAMPLE/HOLD UNIT
ADC
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CONVERTS ANALOG SIGNAL OUTPUT
FROM THE SCANNING EQUIPMENT TO A
DIGITAL SIGNAL SO IT CAN BE
PROCESSED BY A COMPUTER.
SAMPLE/HOLD UNIT (S/H)
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LOCATED BETWEEN AMPLIFIER AND ADC
PERFORMS SAMPLING AND ASSIGNS
SHADES OF GRAY TO THE PIXELS IN THE
DIGITAL MATRIX CORRESPONDING TO
THE STRUCTURES
DAS
GANTRY
X-RAY TUBE
GANTRY CONTROL
DETECTORS
S/H
ADC
DAC
HIGH VOLTAGE
GENERATOR
SCAN CONTROLLER
ARRAY PROCESSOR
HOST
COMPUTER
STORAGE
CONSOLE
IMAGE DISPLAY, RECORDING,
STORAGE
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DISPLAYS IMAGE ( OUTPUT FROM
COMPUTER)
PROVIDES HARD COPY OF THE IMAGE
FACILITATES THE STORAGE AND
RETRIEVAL OF DIGITAL DATA
COMMUNICATES IMAGES IN THE
NETWORK
IMAGE
DISPLAY
IMAGE RECORDING SYSTEMS
(LASER PRINTERS)
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SOLID STATE LASER
PRINTERS
GAS LASER PRINTERS
HARD COPY
IMAGE STORAGE MEDIA
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MAGNETIC TAPES
MAGNETO-OPTICAL DISK (MOD)
CD
COMMUNICATION
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PACS
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 highspeed telecommunications networks and
improved data compression techniques, have
matured in recent years.
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.
CT ROOM LAYOUT