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 DISPLAY, RECORDING, STORAGE SYSTEM DATA ACQUISITION 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

SCANNER

SCANNER GANTRY PATIENT COUCH

GANTRY HOUSES: X-RAY TUBE GENERATOR (LOW VOLTAGE DESIGN) COLLIMATORS DETECTORS

GANTRY CHARACTERISTICS 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 PRODUCTION OF X-RAYS SHAPING OF X-RAY BEAM ENERGY FILTERING X-RAY BEAM

IMAGING SYSTEM COMPONENTS 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 THE FILAMENT SIZE – LENGTH – FOCAL SPOT SMALLER FOCAL SPOT - Low mA SMALLER FOCAL SPOT – sharper image

ANODE +++++ MADE OF TUNGSTEN AND MOLYBDENUM TARGET TARGET MADE OF TUNGSTEN AND RHENIUM

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

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 kVp mA Time INCREASED NOISE

TOO LOW OF kVp: NOISE !!!!

X-RAY EMISSION

TUBE CURRENT CHANGE 2 * mA = 2 * number of photons INTENSITY ENERGY – NO CHANGE CURRENT 2 * mA = 2 * number of photons 4 * mA = 4 * number of photons

Why changing mA or time Avoiding motion – mA time Pediatric technique modification Reducing noise - mAs MOTION NOISE

Tube voltage (kVp) CHANGE INTENSITY - ENERGY – kVp 15% INCREASE OF KVP = 2 * mAs

kVp IN CT 80-140 TOO LOW – NOISE (NOT ENOUGH PENETRATION OF THE PATIENT ) PHOTON STARVATION - NOISE!!!!!

HIGH VOLTAGE GENERATOR –(HVG) GENERATES HIGH VOLTAGE POTENTIAL BETWEEN CATHODE AND ANODE OF AN X-RAY TUBE

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

PRE-PATIENT COLLIMATION POST-PATIENT COLLIMATION COLLIMATION IN CT PRE-PATIENT COLLIMATION POST-PATIENT COLLIMATION ADC

BASIC DATA AQUSITION SCHEME IN CT FILTRATION ADC

FILTRATION CHANGE INTENSITY ENERGY – FILTRATION

TO MAKE THE BEAM HARDER AND FILTRATION MATERIAL ALUMINIUM ( SPECIAL FILTER IN CT) BOWTIE TO MAKE THE BEAM HARDER AND MORE MONOENERGETIC

Filter Patient Detector DEFINES SLICE THICKNESS REDUCES SCATTER RECHING THE PATIENT Detector

CT DETECTORS

DETECTOR TYPES: SCINTILLATION S. CRYSTAL S. CRYSTAL PHOTODIODE PM TUBE

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 CALCIUM TUNGSTATE RARE EARTH OXIDES - CERAMIC

DETECTOR TYPE: GAS IONIZATION XENON GAS 30 ATM

EFFICIENCY OF DETECTORS- QDE SCINTILLATION – 95% - 100%- COMMONLY USED IN III & IV GENERATION SCANNERS GAS – 50% - 60%

COMPUTER SYSTEM RECONSTRUCTION AND POSTPROCESSING CONTROL OF ALL SCANNER COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. DATA FLOW DIRECTION

COMPUTER SYSTEM IN CT MINICOMPUTERS

COMPUTER SYSTEM COMPOSED OF: HARDWARE SOFTWARE

COMPUTER PROCESSING IN CT SEQUENTIAL PROCESSING MULTITASKING MULTIPROCESSING

SOFTWARE –PROGRAM (S) HELPING CT USER TO COMMUNICATE WITH THE CT SYSTEM

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

CT OPERATING SYSTEM UNIX WINDOWS

HOST COMPUTER CONTROL OF ALL COMPONENTS CONTROL OF DATA ACQUSITION, PROCESSING, DISPLAY. DATA FLOW DIRECTION

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) SET OF ELECTRONICS BETWEEN DETECTORS AND HOST COMPUTER. IT CONTAINS: AMPLIFIER, ADC, DAC, GENERATOR, S/H.

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

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) 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 HIGH VOLTAGE GENERATOR DAC S/H ADC SCAN CONTROLLER ARRAY PROCESSOR HOST COMPUTER CONSOLE 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 DISPLAY

IMAGE RECORDING SYSTEMS (LASER PRINTERS) SOLID STATE LASER PRINTERS GAS LASER PRINTERS

HARD COPY

IMAGE STORAGE MEDIA MAGNETIC TAPES MAGNETO-OPTICAL DISK (MOD) CD

COMMUNICATION 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 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