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

2. Computed Tomography Instrumentation And Operation

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

4. 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).

5. 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).

6. 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.

7. 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).

8. 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 ( kV).
13. Power Unit (AC to DC).

9. Gantry Characteristics
Tilting Range, (Tilting Range Of Most Scanners +30 To -30 Degrees).
Aperture, (Most Of The Scanners Have 70 cm Aperture).
70 CM

10. Tilting Of CT Scanner Gantry

11. X-ray Tube And X-Ray Production
The X-ray Tube Axis Is Positioned Perpendicular To The
Imaging Plane To Reduce The Heal Effect.

12. Anode Heal Effect

13. 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

14. 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).

15. 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

16. Noise 15% Increase Of kVp = 2 * mAs
Reduction Of Heat Units – Technique Compensation: kVp, mA, And Time Will Increased Noise.
kVp Range :
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

17. 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

18. 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.

19. Thank You
Best Wishes For All