Computed tomography instrumentation and operation
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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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Computed tomography instrumentation and operation
COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION


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



Scanner1
SCANNER

  • GANTRY

  • PATIENT COUCH


Gantry houses
GANTRY HOUSES:

  • X-RAY TUBE

  • GENERATOR (LOW VOLTAGE DESIGN)

  • COLLIMATORS

  • DETECTORS


Gantry characteristics
GANTRY CHARACTERISTICS

  • APERTURE

  • TILTING RANGE









Patient couch 450 lbs 204 kg distributed weight limit
PATIENT COUCH :450 LBS (204 KG) DISTRIBUTED WEIGHT LIMIT


Scannable range coverage from head to thigh 162cm
SCANNABLE RANGE:COVERAGE FROM HEAD TO THIGH (162CM)



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


kVp

  • Potential difference between cathode and anode (Volts) kilo means 1,000 x.


S time of exposure mas tube current for certain length of time
S –time of exposuremAs tube current for certain length of time


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


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 system in ct
COMPUTER SYSTEM IN CT

  • MINICOMPUTERS


Computer system composed of
COMPUTER SYSTEM COMPOSED OF:

  • HARDWARE

  • SOFTWARE


Computer processing in ct
COMPUTER PROCESSING IN CT

  • SEQUENTIAL PROCESSING

  • MULTITASKING

  • MULTIPROCESSING



CT OPERATING SYSTEM-PROGRAMS THAT CONTROL THE HARDWARE COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER


Ct operating system
CT OPERATING SYSTEM COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • UNIX

  • WINDOWS


Host computer
HOST COMPUTER COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • CONTROL OF ALL COMPONENTS

  • CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY.

  • DATA FLOW DIRECTION


Array processor
ARRAY PROCESSOR COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • 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) COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER.

  • IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H.


Amplifier
AMPLIFIER COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • SIGNAL FROM DETECTORS GOES TO AMPLIFIERS FOR SIGNAL MAGNIFICATION AND THEN IS SENT TO SAMPLE/HOLD UNIT


ADC COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • 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) COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • LOCATED BETWEEN AMPLIFIER AND ADC PERFORMS SAMPLING AND ASSIGNS SHADES OF GRAY TO THE PIXELS IN THE DIGITAL MATRIX CORRESPONDING TO THE STRUCTURES


DAS COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

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 COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • 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 DISPLAY COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER


Image recording systems laser printers
IMAGE RECORDING SYSTEMS COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER(LASER PRINTERS)

  • SOLID STATE LASER PRINTERS

  • GAS LASER PRINTERS


Hard copy
HARD COPY COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER


Image storage media
IMAGE STORAGE MEDIA COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • MAGNETIC TAPES

  • MAGNETO-OPTICAL DISK (MOD)

  • CD


Communication
COMMUNICATION COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

  • PACS


Overread network

OVERREAD NETWORK COMPONENTS AND THE OVERALL OPERATION OF THE CT COMPUTER

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.


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
CT ROOM LAYOUT 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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