Download presentation

1
**Computed Tomography Principles**

Ge Wang, Ph.D. Department of Radiology University of Iowa Iowa City, Iowa 52242, USA

2
**Learning Objectives CT terms Data acquisition**

Basic elements of CT scanner Scanning modes Image reconstruction Spiral/helical CT Image resolution and artifacts Interaction among imaging parameters Quality assurance Radiation exposure

3
A Little Bit History Nobel prizes Roentgen (1901): Discovery of X-rays Hounsfield & Cormack (1979): Computed tomography

4
**Computed Tomography Principles**

1. Projection measurement 2. Scanning modes 3. Scanner systems 4. Image reconstruction

5
**X-ray Interactions - Photoelectric Effect**

(From Aracor) Photoelectric effect results in total absorption of the X-ray photon and the emission of a bound electron

6
**X-ray Interactions - Compton Scatter**

(From Aracor) Compton Scatter results in a free electron & a scattered (less energetic) photon

7
Source and Detectors Source - Rotating anode disk - Small focal spot down to 0.6 mm - Polychromatic beam Detectors - Xenon (50-60%) - Scintillation (>90%) (From Siemens)

8
**Exponential Attenuation of X-ray**

Ni No m Ni: input intensity of X-ray No: output intensity of X-ray m: linear X-ray attenuation x Ni No x Attenuated more X-rays

9
**Ray-Sum of X-ray Attenuation**

Ni No k x Ray-sum Line integral

10
**Projection & Sinogram y P(t) t p x f(x,y) t X-rays Sinogram**

Projection: All ray-sums in a direction Sinogram: All projections y P(t) t p x f(x,y) t X-rays Sinogram

11
**Completeness Condition**

There exists at least a source on any line intersecting a cross-section

12
**Computed Tomography Principles**

1. Projection measurement 2. Scanning modes 3. Scanner systems 4. Image reconstruction

13
First Generation One detector Translation-rotation Parallel-beam

14
**Second Generation Multiple detectors Translation-rotation**

Small fan-beam

15
**Third Generation Multiple detectors Translation-rotation**

Large fan-beam

16
Fourth Generation Detector ring Source-rotation Large fan-beam

17
**Third & Fourth Generations**

(From Picker) (From Siemens)

18
**Spiral/Helical Scanning**

Simultaneous Source rotation Table translation Data acquisition

19
Cone-Beam Geometry

20
**Scanning modes First generation One detector, translation-rotation**

Parallel-beam Second generation Multiple detectors, translation-rotation Small fan-beam Third generation Multiple detectors, rotation-rotation Large fan-beam

21
**Scanning modes Fourth generation Detector ring, source-rotation**

Large fan-beam Spiral/Helical scanning, cone-beam geometry

22
**Computed Tomography Principles**

1. Projection measurement 2. Scanning modes 3. Scanner systems 4. Image reconstruction

23
**Spiral CT Scanner Network Gantry Source Computer Parallel processor**

Display Control console Table Recording Detectors Data acquisition system Storage units: Tapes, disks

24
**Data Acquisition System (DAS)**

Pre-Collimator Post-Collimator Scattering Source Detector Filter Patient

25
**Data Acquisition System (DAS)**

X-ray Tube Source Filter Detectors CT Gantry (From Siemens) Detector

26
**Spiral CT Scanner Gantry Data acquisition system Table Computer**

Parallel processors Control console Storage units Tapes, disks Recording device Network interface X-ray generator Heat exchanger (From Elscint)

27
**E-Beam CT Scanner Speed: 50, 100 ms Thickness: 1.5, 3, 6, 10 mm**

ECG trigger cardiac images (From Imatron)

28
**Computed Tomography Principles**

1. Projection measurement 2. Scanning modes 3. Scanner systems 4. Image reconstruction

29
Computed Tomography y Computed tomography (CT): Image reconstruction from projections t P(t) P(t) f(x,y) x f(x,y) X-rays

30
Reconstruction Idea =4 2=3 3=2 4=1

31
**Algebraic Reconstruction Technique (ART)**

3 2 4 1 6 -2 Update a guess based on data differences Guess 1 Guess 0 Guess 2 Error

32
**Fourier Transformation**

f(x,y) F(u,v) Fourier Transform Image Space Fourier Space

33
**Fourier Slice Theorem y P(t) v t F[P(t)] u x F(u,v) f(x,y)**

X-rays v F[P(t)] u F(u,v)

34
**From Projections to Image**

y x v u F-1[F(u,v)] f(x,y) P(t) F(u,v)

35
**Filtered Backprojection**

f(x,y) P(t) P’(t) 1) Convolve projections with a filter 2) Backproject filtered projections

36
Example: Projection Projection Projection Sinogram Ideal Image

37
**Example: Backprojection**

38
**Example: Backprojection**

Sinogram Backprojected Image

39
Example: Filtering Sinogram Filtered Sinogram

40
**Example: Filtered Backprojection**

Filtered Sinogram Reconstructed Image

41
References T. S. Curry III, J. E. Dowdey, R. C. Murry Jr. Christensen’s physics of diagnostic Radiology (4th edition), Lea & Febiger (for residents) G. Wang, M. W. Vannier: Computerized tomography. Encyclopedia of Electrical and Electronics Engineering, edited by Webster JG, to be published by John Wiley & Sons (for engineers) (on-line slides & handouts in the Teaching section)

Similar presentations

OK

CT Physics V.G.Wimalasena Principal School of radiography.

CT Physics V.G.Wimalasena Principal School of radiography.

© 2018 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on dc shunt motor Ppt on conservation of momentum lab Creating ppt on ipad Download ppt on ohm's law for class 10 Ppt on intellectual property rights and global business Ppt on biography of william shakespeare Ppt on fire extinguisher training Ppt on energy cogeneration Ppt on presentation skills communication Ppt on search engine of internet