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COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION. OUTLINE. CT SYSTEM COMPONENTS – DEFINITION OF A SCANNER SCANNER COORDINATE SYSTEM – XYZ, ISOCENTER IMAGING SYSTEM COMPUTER SYSTEM DISPLAY, RECORDING, AND STORAGE SYSTEMS. CT MAIN SYSTEMS. IMAGING SYSTEM COMPUTER SYSTEM

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outline
OUTLINE
  • CT SYSTEM COMPONENTS – DEFINITION OF A SCANNER
  • SCANNER COORDINATE SYSTEM – XYZ, ISOCENTER
  • IMAGING SYSTEM
  • COMPUTER SYSTEM
  • DISPLAY, RECORDING, AND STORAGE SYSTEMS
ct main systems
CT MAIN SYSTEMS
  • IMAGING SYSTEM
  • COMPUTER SYSTEM
  • DISPLAY, RECORDING, STORAGE SYSTEM
  • DATA ACQUISITION SYSTEM
ct system
CT SYSTEM

GANTRY

X-RAY TUBE

GANTRY CONTROL

DETECTORS

HIGH VOLTAGE

GENERATOR

DAC

S/H

ADC

SCAN CONTROLLER

ARRAY PROCESSOR

HOST

COMPUTER

CONSOLE

STORAGE

scanner6
SCANNER
  • GANTRY
  • PATIENT COUCH
gantry houses
GANTRY HOUSES:
  • X-RAY TUBE
  • GENERATOR (LOW VOLTAGE DESIGN)
  • COLLIMATORS
  • DETECTORS
gantry characteristics
GANTRY CHARACTERISTICS
  • APERTURE
  • TILTING RANGE
imaging system
IMAGING SYSTEM
  • PRODUCTION OF X-RAYS
  • SHAPING OF X-RAY BEAM ENERGY
  • FILTERING X-RAY BEAM
imaging system components
IMAGING SYSTEM COMPONENTS
  • X-RAY TUBE
  • GENERATOR –HIGH VOLTAGE
  • COLLIMATORS
  • FILTER
  • DETECTORS
  • DETECTOR ELECTRONICS
cathode made of tungsten
CATHODE --------MADE OF TUNGSTEN

IN CT – STILL SMALL AND LARGE

thermionic emission
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
FOCAL SPOT- CT UTILIZES DIFFERENT FOCAL SPOTS
  • THE FILAMENT SIZE – LENGTH – FOCAL SPOT

SMALLER FOCAL SPOT - Low mA

SMALLER FOCAL SPOT – sharper image

anode made of tungsten and molybdenum
ANODE +++++ MADE OF TUNGSTEN AND MOLYBDENUM

TUNGSTEN

TARGET

TARGET MADE OF TUNGSTEN

AND

RHENIUM

ma tube current
mA – tube current
  • The number of electrons flowing from cathode to anode
slide27
kVp
  • Potential difference between cathode and anode (Volts) kilo means 1,000 x.
x ray production results in a lot of heat and very little x rays being generated
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

too low of kvp
TOO LOW OF kVp:
  • NOISE !!!!
tube current change
TUBE CURRENT CHANGE

INTENSITY

ENERGY – NO CHANGE

CURRENT

2 * mA = 2 * number of photons

4 * mA = 4 * number of photons

why changing ma or time
Why changing mA or time
  • Avoiding motion – mA time
  • Pediatric technique modification
  • Reducing noise - mAs

MOTION

NOISE

tube voltage kvp change
Tube voltage (kVp) CHANGE

INTENSITY -

ENERGY–

kVp

15% INCREASE OF KVP = 2 * mAs

kvp in ct
kVp IN CT
  • 80-140
  • TOO LOW – NOISE

(NOT ENOUGH PENETRATION OF THE PATIENT )

PHOTON STARVATION - NOISE!!!!!

high voltage generator hvg
HIGH VOLTAGE GENERATOR –(HVG)
  • GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBE
ct generator
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

collimation in ct
COLLIMATION IN CT

PRE-PATIENT COLLIMATION

POST-PATIENT COLLIMATION

ADC

filtration change
FILTRATION CHANGE

INTENSITY

ENERGY –

FILTRATION

filtration material
FILTRATION MATERIAL
  • ALUMINIUM ( SPECIAL FILTER IN CT)

BOWTIE

TO MAKE THE BEAM HARDER AND

MORE MONOENERGETIC

slide43

Filter

DEFINES SLICE

THICKNESS

Patient

REDUCES SCATTER

RECHING THE PATIENT

Detector

detector types scintillation
DETECTOR TYPES: SCINTILLATION

S. CRYSTAL

S. CRYSTAL

PHOTODIODE

PM TUBE

scintillation crystals used with pm tubes
SCINTILLATION CRYSTALS USED WITH PM TUBES:
  • SODIUM IODIDE –AFTERGLOW + LOW DYNAMIC RANGE ( USED IN THE PAST)
  • CALCIUM FLUORIDE
  • BISMUTH GERMANATE
s crystal used with photodiode
S. CRYSTAL USED WITH PHOTODIODE
  • CALCIUM TUNGSTATE
  • RARE EARTH OXIDES - CERAMIC
efficiency of detectors qde
EFFICIENCY OF DETECTORS- QDE
  • SCINTILLATION – 95% - 100%- COMMONLY USED IN III & IV GENERATION SCANNERS
  • GAS – 50% - 60%
computer system
COMPUTER SYSTEM
  • RECONSTRUCTION AND POSTPROCESSING
  • CONTROL OF ALL SCANNER COMPONENTS
  • CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY.
  • DATA FLOW DIRECTION
computer processing in ct
COMPUTER PROCESSING IN CT
  • SEQUENTIAL PROCESSING
  • MULTITASKING
  • MULTIPROCESSING
slide55
CT OPERATING SYSTEM-PROGRAMS THAT CONTROL THE HARDWARE COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER
host computer
HOST COMPUTER
  • CONTROL OF ALL COMPONENTS
  • CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY.
  • DATA FLOW DIRECTION
array processor
ARRAY PROCESSOR
  • 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
DATA ACQUISITION SYSTEM (DAS)
  • SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.
  • IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H.
amplifier
AMPLIFIER
  • SIGNAL FROM DETECTORS GOES TO AMPLIFIERS FOR SIGNAL MAGNIFICATION AND THEN IS SENT TO SAMPLE/HOLD UNIT
slide61
ADC
  • 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
SAMPLE/HOLD UNIT (S/H)
  • LOCATED BETWEEN AMPLIFIER AND ADC PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO THE STRUCTURES
slide63
DAS

GANTRY

X-RAY TUBE

GANTRY CONTROL

DETECTORS

HIGH VOLTAGE

GENERATOR

DAC

S/H

ADC

SCAN CONTROLLER

ARRAY PROCESSOR

HOST

COMPUTER

CONSOLE

STORAGE

image display recording storage
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
image recording systems laser printers
IMAGE RECORDING SYSTEMS(LASER PRINTERS)
  • SOLID STATE LASER PRINTERS
  • GAS LASER PRINTERS
image storage media
IMAGE STORAGE MEDIA
  • MAGNETIC TAPES
  • MAGNETO-OPTICAL DISK (MOD)
  • CD
overread network

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.

slide71

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.