COMPUTED TOMOGRAPHY - I RAD 365 CT - Scan Prepared By: Ala’a Ali Tayem Abed

COMPUTED TOMOGRAPHY INSTRUMENTATION AND OPERATION

OUTLINE CT SYSTEM COMPONENTS. SCANNER COORDINATE SYSTEM – XYZ, ISOCENTER. IMAGING SYSTEM. COMPUTER SYSTEM . DISPLAY, RECORDING, AND STORAGE SYSTEMS.

5. Image Archival (Recording). CT MAIN SYSTEMS IMAGING SYSTEM. DATA ACQUISITION SYSTEM, Analog-to-Digital Converter (ADC). COMPUTER SYSTEM. DISPLAY, RECORDING, STORAGE SYSTEM. Phases of CT imaging 1. Scanning the patient. 2. Data Acquisition. A. Tube or tube and detector move. B. Multiple attenuation measurements are taken around the object. 3. Image reconstruction. 4. Image Display. 5. Image Archival (Recording).

CT Gantry External View Gantry Aperture (70 cm diameter). Microphone. Sagittal laser Alignment Light. Patient guide lights. X-ray exposure indicator light. Emergency stop buttons. Gantry control panels. External laser alignment lights. Patient Couch.

CT Gantry Control Panel Gantry Tilt (+/-30 degrees). Laser Alignment Lights on/off. Couch in/out. Free (manual) Couch Movement. Zero Couch Position. Couch up/down. Home Button (couch out & down).

CT Gantry Internal View 1. X-Ray Tube. 2. Filters, Collimator. 4. X-Ray tube heat exchanger (Oil Cooler). 5. High Voltage Generator (0-75 kV) 6. Direct Drive Gantry Motor. 7. Rotation Control Unit. 8. Data Acquisition System (DAS). 9. Detectors. 10. Slip Rings. 11. Detector Temperature Controller 12. High Voltage Generator (75-150 kV). 13. Power Unit (AC to DC).

GANTRY CHARACTERISTICS TILTING RANGE, (TILTING RANGE OF MOST SCANNERS +30 TO -30 DEGREES. APERTURE, (MOST OF THE SCANNERS HAVE 70 cm APERTURE). 70 CM

TILTING OF CT SCANNER GANTRY

COORDINATE SYSTEM X Y Z

ISOCENTER

IMAGING SYSTEM SCANNER GANTRY HOUSES: X-RAY TUBE. PATIENT COUCH : GENERATOR. COLLIMATORS. DETECTORS. PATIENT COUCH : 450 Pounds (204 KG) DISTRIBUTED WEIGHT LIMIT. SCANNABLE RANGE: COVERAGE FROM HEAD TO THIGH (162 cm). IMAGING SYSTEM COMPONENTS: GENERATOR – HIGH VOLTAGE. FILTER. DETECTOR ELECTRONICS.

X-RAY TUBE AND X-RAY PRODUCTION The x-ray tube axis is positioned perpendicular to the imaging plane to reduce the heal effect.

Anode Heal Effect

THERMIONIC EMISSION CATHODE ( - ) ITS CONSIST OF FILAMENT HEATED UP TO AT LEAST 2,200 DEG. CELSIUS, TO LIBERATE ELECTRONS FOR TRANSIT TO ANODE. CATHODE: MADE OF TUNGSTEN

SMALLER FOCAL SPOT – sharper image. ANODE ( + ) MADE OF TUNGSTEN AND MOLYBDENUM TUNGSTEN TARGET FOCAL SPOT- CT UTILIZES DIFFERENT FOCAL SPOTS. SMALE FOCAL SPOT, AND LARGE FOCAL SPOT. SMALLER FOCAL SPOT – sharper image. CT large focal spots (1 mm) are used at high power ratings (up to 60 kW). The small focal spot (0.6 mm) is used at low power ratings below about 25 kW.

HEAT UNITS CALCULATION HU= kVp X mA x time MOST CT TUBES HEAT CAPACITY mA – tube current: The number of electrons flowing from cathode to anode. kVp: Potential difference between cathode and anode, kilo (Volts). S: time of exposure in second. 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

15% INCREASE OF KVP = 2 * mAs INTENSITY kVp ENERGY REDUCTION OF HEAT UNITS – TECHNIQUE COMPENSATION: kVp, mA, and time will INCREASED NOISE. kVp Range : 80-140. TOO LOW OF kVp: INCREASED NOISE. (NOT ENOUGH PENETRATION OF THE PATIENT ) - PHOTON STARVATION NOISE!!!!! Tube voltage (kVp) CHANGE: INTENSITY ENERGY kVp 15% INCREASE OF KVP = 2 * mAs

Why changing mA or time???? NOISE MOTION Avoiding motion – time TUBE CURRENT CHANGE ( mA ): INCREASING CURRENT WILL INCREAS INTENSITY, AND ENERGY – NO CHANGE. Why changing mA or time???? Avoiding motion – time Pediatric technique modification. Reducing noise - mAs NOISE MOTION

2. HIGH VOLTAGE GENERATOR – (HVG) Generates high voltage potential between cathode and anode of an X- Ray tube. All CT imaging system operate on high frequency power. A high – frequency generator is small because the high – voltage step – up transformer is small, so it can be mounted on the rotating gantry. KVP SELECTION ( Tube Potential ): 80, 100, 120, 130,140. mA selection ( Tube Current ): 20, 30, 50, 65, 100, 125, 150, 175, 200, 400, 500.

Thank You Best Wishes For All