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

Computed Tomography Instrumentation And Operation

Outline CT System Components. Imaging System. Computer System . Display, Recording, And Storage Systems.

5. Image Archival (Recording). Phases Of CT Imaging 1. Scanning The Patient. 2. Data Acquisition. Multiple Attenuation Measurements Are Taken Around The Object. 3. Image Reconstruction. 4. Image Display. 5. Image Archival (Recording).

Imaging System Scanner: Gantry. Patient Couch. Gantry Houses: X-ray Tube. Generator. Filter. Collimators. Detectors. Patient Couch : 450 Pounds (204 Kg) Distributed Weight Limit. Scannable Range: Coverage From Head To Thigh (162 Cm).

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

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

Focal Spot- CT Utilizes Different Focal Spots. Anode ( + ) Made Of Tungsten And Molybdenum. TUNGSTEN TARGET Focal Spot- CT Utilizes Different Focal Spots. Small Focal Spot, And Large Focal Spot. Smaller Focal Spot – Sharper Image. The CT Large Focal Spot (1 mm). The CT Small Focal Spot (0.6 mm).

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

Noise 15% Increase Of kVp = 2 * mAs 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 ) Tube Voltage (kVp) Change: Intensity Energy Noise kVp 15% Increase Of kVp = 2 * mAs

NOISE MOTION Why Changing mA or time???? Tube Current Change ( mA ): Increasing Current Will Increase 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, 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