Generations of Computer Tomography (CT))

by G.K.R. Senadeera 9/22/2015

Lay out 1. CT in brief 2. Generation types & their features (i) First generation: rotate/translate,pencil beam with one detector

(ii)Second generation: rotate/translate, narrow fan beam, multiple detectors

(iii) Third generation: rotate/rotate, wide fan beam (iv) Forth generation: rotate/stationary, with detector ring (v). Fifth generation: electron beam CT (vi). Sixth generation: helical (or spiral) CT (vii). Seventh generation: multiple detector array 3. Summary 4. References 2

CT: The beginning CT founded in 1970 by Sir Godfrey Hounsfield

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CT combines X radiation and radiation detectors coupled with a computer to create cross sectional image of any part of the body. Equipment Arrangement Radiography v/s Tomography Cross-sectional slices

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CT scanners are categorized into several generations depending on the Type of detectors,

Scanning method etc.

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First Generation Scanners  Single detector, single x-ray tube, rotate/translate pencil beam system, rotation angle/step 1°  Long scan time 5 min  Over night image reconstruction  Poor spatial resolution  Best scatter rejection  Designed only for evaluation of brain  The axis of rotation passed through the centre of the patient’s head 9/22/2015

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• Head kept enclosed in a water bath • Two side-by-side detectors • A reference detector

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Second Generation Scanners Linear array of about 30 detectors, single x-ray tube, rotate/translate motion, narrow angle (10 ° ) fan beam rotation angle/step 10° Shortest scan time was about 18 s per slice

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Third Generation Scanners Linear array of about 800 detectors, single x-ray tube, rotate/rotate motion only, wide fan beam (500-550) to cover the entire patient Scan time of newer scanners is about ½ s per slice Can produce ring artifacts

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Fourth Generation Scanners Complete circular array of about 4800 stationary detectors Single x-ray tube rotates with in the circular array of detectors Wide fan beam to cover the entire patient Scan time of newer scanners is about ½ s per slice Designed to address ring artifacts 9/22/2015

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Fifth Generation Scanners

Electron Beam CT (EBCT)

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Fifth Generation Scanners ctd 210° arc array of stationary detectors x-rays are produced from the focal track as high energy electron beam strikes the tungsten target Scan time is about 50 ms per slice Developed for cardiac tomographic imaging

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5th generation: ctd….

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6th Generation CT (Helical) (1990)

Eliminating interscan delays- Slip ring concept

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* Allows the complete elimination of interscan delays * Slip ring passes electrical power to the rotating components (X ray tune and Detectors) without fixed connections. 9/22/2015

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6th Generation CT (Helical) ctd… Patient is transported continuously through gantry

while data are acquired c continuously during several 360 o rotations. By avoiding the time require to translate the patient table, the total scan time required to image the patient can be much shorter.  Allow the use of less contrast agent and increase patient throughput  In some instances the entire scan be done within a single breath-hold of the patient. 9/22/2015

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*

7th Generation : Multiple detector Array

When using multiple detector arrays, the collimator spacing is wider and more of the X rays that are produced by the tube are used in producing image data. ---Opening up the collimator in a single array scanner increase the slice thickness, reducing spatial resolution in the slice thickness ---With multiple detector array scanners, slice thickness is determined by detector size not by collimator. 9/22/2015

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Advantages of Multiple detector Array

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Summary Generation

Configuration

Detector

Beam

Min scan time

First

Translate rotate

1-2

Pencil thin

2.5min

Second

Translate rotate

3-52

Narrow fan

10sec

Third

Rotate- rotate

256-1000

Fourth

Rotate- fixed

Fifth

Electron beam

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Adv

Dis AdV

Wide fan 0.5sec

Better predetector collimation

Ring artifact

600-4800

Wide fan 0.5sec

Avoid ring artifact

Higher Patient Dose (tube close to Pt.)

1284

Wide fan 50ms electron beam

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References 1. “Computer Tomography”, PPT presentation by Moustafa M. Mohamed. 2. “Computer Tomography”, PPT presentation by Lovnish Thakur 3. “Basic & Conceptual Information about Computed Tomography” PPT presentation by by Maulik R. Shah. 4. “ Basic Principles of CT scanning” PPT presentation by NG. Hareesha 9/22/2015

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SOME OF IMAGE FORMED BY CT SCAN

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Thank you

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1FGKRS Generations ofCT.pdf

(iii) Third generation: rotate/rotate, wide fan beam. (iv) Forth generation: rotate/stationary, with detector ring. (v). Fifth generation: electron beam CT. (vi).

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