The document provides details on the key components of a computed tomography (CT) scanner. It discusses the gantry, which houses the x-ray tube, detector array, and high voltage generator. It describes different types of x-ray tubes, detectors, including scintillation and gas ionization detectors, and collimators. The computer is also highlighted as a crucial component, processing the data collected and representing the cross-sectional images.

1. ‫تعلم‬ ‫تكن‬ ‫مالم‬ ‫وعلمك‬
‫هللا‬ ‫فضل‬ ‫وكان‬
‫عظيما‬ ‫عليك‬

2. Basics Of Computed
Tomography (CT)
Lecture Four
Gamal Fathalla M.
Mahdaly
gamal_mahdaly@hotmail.com

4. (1) Gantry
The gantry contains :
 (a) The x-ray tube
 (b) The detector array
 (c) The high voltage generator

5. CT Scanner main components

6. The gantry houses imaging components such as the x-ray tube
and generator, slip rings, collimators, detectors and detector electronics

7. X-RAY TUBE

8. (a) X-ray Tube
 The anode heating capacity must be high,
at least several million heat unit (8-MUH).
 High speed rotators are used for best heat
dissipation.
 Small focal spot size.
 X-ray tubes are energized with either a
continuous or a pulsed x-ray beam.

9. Special features of x-ray tube
 Internal getters (ion pumps) completely
evacuate air from the tube.
 Large anode disks e.g. 200 mm
(conventional tube disk 120 – 160 mm).
 The anode disk is thicker than
conventional all metal disk.

10. Three types of disk designs for modern x-ray tubes used
in CT:
A, conventional all-metal disk, B, brazed graphite anode disk
and C, chemical vapor deposition ( CVD) graphite disk.

11. Slip-Ring Technology
 Electromechanical devices consisting of
circular electrical conductive rings and
brushes that transmit electrical energy
cross a rotating interface.
 Design in form of disk or cylinder.
 Power supply low-voltage or high voltage.

12. (b) Detector assembly
 Early CT scanners had one detector.
 Modern CT scanner have multiple.
 A detector must has the following characteristics:
1. High Efficiency.
2. Suitable Response time.
3. Flexible Dynamic range.
4. High reproducibility and stability.

13. Types of Detectors
 Scintillation Detector
Convert x-ray to light
 Gas Ionization Detector
Convert x-ray energy directly to electrical
energy.

14. Scintillation Detectors
Contain:
 1-Crystal:
Sodium iodide
Bismuth germinate
Cesium iodide
Cadmium tungestate
 2- Photomultiplier or photodiode.

15. Scintillation crystal detection
and conversion scheme.

16. Schematic representation of a scintillation
detector based on the photomultiplier

17. A: Basic structure of a photodiode.
B: The electronic symbol of a photodiode

18. Scintillation detector
 Spacing 8 / mm or 1-5 /degree
 Detection efficiency 90%
 Inter-space 50%
 Over all efficiency 45%

19. Gas detectors
 Made from high atomic number inert gas
xenon, or xenon krypton mixture.
 Spacing 1 mm interval.
 Detection efficiency 45%
 Over all efficiency 45%

20. Detectors and Detector Arrays
Most modern CT
systems use either
Xenon detectors (old
technology) or solid-
state scintillation
detectors

22. Conversion of X-rays into electrical
energy through gas ionization.

23. The configuration of a gas ionization detector
consists of series of individual gas chambers
separated by tungsten plates.

25. OVERALL DETECTOR EFFICIENCY OF A GAS-FILLED DETECTOR
ARRAY IS APROXIMATELY EQUAL TO THAT OF THE
SCINTILLATION DETECTOR ARRAY

26. Detector efficiency is important

27. (c) X-ray Generator
 Three-phase power
 High-frequency generator

28. (d) Collimation
 Pre-patient collimator
 Post patient or pre-detector collimator.
 Required for the same reasons as that is
required in conventional radiography:
1* Reduction of patient exposure & scattered radiation.
2* Enhancing the image contrast.

29. Collimation

31. (2) Computer
 Large capacity computer
 Microprocessor or array processor
 Costs 1/3 of the total cost.

32. Any Question???.
Take your Tiiime!!! .
Again Any Question???.
Otherwise, I’m going to ask!!!.
Should I Ask???.

33. Have a nice day