computed tomography is an method of examining the body organs.it is originally known as computed axial tomography. PRINCIPLE-It uses ionizing radiation or x rays ,coupled with an electronic detector array to record a pattern of densities and to create an image. GANTRY-Donut shape.It contain the scanner, x ray tube as well as detectors that generate and detect x rays. Two type-Scintillation detectors and gas filled detector OPERATING CONSOLE-Used to input all the factors related to taking a scanner (KVp, mA, Scan time ,Slice thickness etc.) Two different console One is Used by CAT Scanner operators and other by physicians.different generation of CT ie, first,second,third and fourth. QA tests Alignment of gantry laser-To verify the gantry lasers are parallel and orthogonal with the imaging plane,To verify that the wall lasers are accurately spaced from the scan plane,To verify proper identification of scan plane with gantry laser,Tolerance limit +/- 2mm,Should be done monthly and after laser adjustment, Gantry tilt-To verify the accuracy of gantry tilt indicators To verify that the gantry accurately return to nominal position after tilting Tolerance limit +/- 1mm or +/-1 degree Should be done annually. Generator tests-To verify the proper operation of a x ray generator.Should be done after the replacement of generator components Radiation profile width-To verify the radiation profile width meets the specification of manufacture.To verify that the sensitivity profile width meets the manufacturer specification.This is optional if the CTDI (computed tomography dose index) accuracy has been verified.Tolerance limit is specified by the manufacture.Should be done annually CT number accuracy-Daily-CT number for water.Monthly-4 to 5 different materials.Annually-electron density phantom.Tolerance limit for water 0 +/- 5 HU. In plane spatial integrity-Daily- x or y direction,Monthly- both direction,Tolerance limit +/-1mm

1. COMPUTED TOMOGRAPY
ATHULIYA K

2. • CT is an method of examining body organs
• Originally known as computed axial tomography (CAT).
• PRINCIPLE
– It uses ionizing radiation or x rays ,coupled with an
electronic detector array to record a pattern of densities
and to create an image.

3. • MAIN COMPONENTS OF CT SCANNER
– CT SCANNER
– GANTRY
– DATAACQUISITION SYSTEM
– OPERATING CONSOLE

4. • GANTRY
– Donut shape
– It contain the scanner, x ray tube as well as detectors that
generate and detect x rays

5. • DETECTORS
– Two type
• Scintillation detectors
• gas filled detectors
– Gas filled detectors
• Xenon
• Kryton
Pressurised xenon gas  ionization  signal
– Scintillation detectors
• Sodium iodide
• Cesium iodide
Scintillation  photon capture  light  photodiode
 signal

6. • DATA ACQUISITION SYSTEM
Detector
current to voltage converter
preamplifier
analog integrator
analog to digital converter
computer

7. • OPERATING CONSOLE
• Used to input all the factors related to taking a scanner
(KVp, mA, Scan time ,Slice thickness etc.)
• Two different console
– Used by CAT Scanner operators
– Used by physicians

8. • GENERATIONS
FIRST
Translate rotate configuration
1-2 detectors
narrow thin beam

9. SECOND
Translate rotate configuration
3-52 detectors
Narrow fan beam

10. THIRD
Rotate rotate configuration
256-1000 detectors
Wide fan of beam

11. FOURTH
Rotate fixed configuration
600-4800 detectors
Wide fan of beam

12. • QA TESTS
– Alignment of gantry laser
• To verify the gantry lasers are parallel and orthogonal with
the imaging plane
• To verify that the wall lasers are accurately spaced from the
scan plane
• To verify proper identification of scan plane with gantry laser
• Tolerance limit +/- 2mm
• Should be done monthly and after laser adjustment

13. – Gantry tilt
• To verify the accuracy of gantry tilt indicators
• To verify that the gantry accurately return to nominal
position after tilting
• Tolerance limit +/- 1mm or +/-1 degree
• Should be done annually
– Generator tests
• To verify the proper operation of a x ray generator
• Should be done after the replacement of generator
components

14. – Radiation profile width
• To verify the radiation profile width meets the
specification of manufacture
• To verify that the sensitivity profile width meets the
manufacturer specification
• This is optional if the CTDI (computed tomography dose
index) accuracy has been verified
• Tolerance limit is specified by the manufacture
• Should be done annually

15. – CT number accuracy
• Daily-CT number for water
• Monthly-4 to 5 different materials
• Annually-electron density phantom
• Tolerance limit for water 0 +/- 5 HU
– Electron density to CT number
– Spatial resolution
– Contrast resolution
Should be done annually.
Tolerance limit is specified
by the manufacture

16. – In plane spatial integrity
• Daily- x or y direction
• Monthly- both direction
• Tolerance limit +/-1mm
– Field uniformity
• Monthly- verify the commonly used kvp