Computed Tomography Presented By:- Goutam Mohanty M.Tech In Bioelectronics Dept. Of ECE,Tezpur University

Contents Introduction Introduction Basic Principle System of component System of component Advantages Advantages Disadvantages Disadvantages Artifact Artifact Typical scan doses Typical scan doses Conclusion Conclusion

Introduction  Tomography is the Greek word consists of two words : Tomos + graphic  Computed tomography (CT) is a medical imaging method employing tomography. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation.  CT was invented by G.N. Hounsfield at central research laboratories of EMI Ltd,UK in G.N. Hounsfield G.N. Hounsfield

 In CT, X-rays from a finely collimated source are made to pass through a slice of the object or patient from variety of directions.  The x-ray tube & photographic film are moved in synchronization so that one plane of the patient under examination remains in focus while all other planes are blurred.  Then the picture is made by viewing the patient via x-ray imaging numerous angle by mathematically reconstructing the detailed structures & displaying the reconstructed image on a video monitor.  In the above process,the x-ray beams are attenuated which is described by the given equation: Basic Principle

(Technique of producing CT images)

CT scanner

SYSTEM COMPONETS:- CT systems consists of the following four major subsystems: CT systems consists of the following four major subsystems: Scanning system:-This takes suitable readings for a picture to be Scanning system:-This takes suitable readings for a picture to be reconstructed and including X-ray source & detectors. Processing unit:- This converts these reading into intelligible picture Processing unit:- This converts these reading into intelligible picture information. information. Viewing part:- It presents this information in visual form & includes other manipulative aids to assist diagnosis. Viewing part:- It presents this information in visual form & includes other manipulative aids to assist diagnosis. Storage unit :- This enables the information to be stored for Storage unit :- This enables the information to be stored for subsequent analysis.

scanning system:- 1st generation:- Parallel beam generation 1st generation:- Parallel beam generation 2nd generation:- Fan beam, multiple detectors 2nd generation:- Fan beam, multiple detectors 3rd generation:- Fan beam, rotating detectors 3rd generation:- Fan beam, rotating detectors 4th generation:- Fan beam,fixed detectors 4th generation:- Fan beam,fixed detectors 5th generation:- Scanning electron beam 5th generation:- Scanning electron beam Spiral / Helical scanning:-It is used for 3D visualization / image of a slice Spiral / Helical scanning:-It is used for 3D visualization / image of a slice  X-ray source:-Two main types of X-ray tubes have been utilized for CT. Oil-cooled fixed anode line focus continuous tube Oil-cooled fixed anode line focus continuous tube Rotating anode air- cooled pulsed X-ray source. Rotating anode air- cooled pulsed X-ray source.  Detectors:-For a good image quality a, detectors play a significant role.

Scanning arrangements

Fig (e) Fig(f)

Processing system:-  Data Acquisition System:- A typical DAS shown in figure It consist of precision pre-amplifiers, current to voltage converter, analog integrators, multiplexers & analog to digital converters. It consist of precision pre-amplifiers, current to voltage converter, analog integrators, multiplexers & analog to digital converters. (Fig for DAS)

 Processing unit:- The information received by computer from the scanning gantry needs to be processed for the reconstructing the pictures. The information received by computer from the scanning gantry needs to be processed for the reconstructing the pictures. The reconstruction methods can be classified into the following three major techniques The reconstruction methods can be classified into the following three major techniques  Back projection:- Analogous to graphic reconstruction  Iterative method:-  The iterative or successive approximation method may be used to obtain an image of attenuation co-efficient the measured intensity data.  More & more iterations,the image matrix matches more &more closely with the object matrix.  Analytical method / Convolution method / Filters:-   Reconstruction using variations of Fast Fourier Transforms (FFT).  The use of this method enables pictures to be reconstructed within a few seconds.

(Principle of iterative reconstruction method)

(Block diagram of the image computer)

 Computer system:-It plays a central role in CT scan.  Viewing system:-  The final picture is available on a television type picture tube.It have window level & window width control.These controls determine where & over what range of CT numbers will the video gray scale possible lie.  Storing and Documentation:-  This is required for subsequent processing or evaluation of CT Scan.

Advantages:- CT scanning is painless, noninvasive and accurate. CT scanning is painless, noninvasive and accurate. A major advantage of CT is that it is able to image bone, soft tissue and blood vessels all at the same time. A major advantage of CT is that it is able to image bone, soft tissue and blood vessels all at the same time. CT scanning provides very detailed images of many types of tissue. CT scanning provides very detailed images of many types of tissue. CT examinations are fast and simple. CT examinations are fast and simple. CT is less sensitive to patient movement than MRI. CT is less sensitive to patient movement than MRI. CT can be performed if you have an implanted medical device of any kind, unlike MRI. CT can be performed if you have an implanted medical device of any kind, unlike MRI. No radiation remains in a patient's body after a CT examination. No radiation remains in a patient's body after a CT examination.

Disadvantages:- There is always a slight chance of cancer from excessive exposure to radiation. There is always a slight chance of cancer from excessive exposure to radiation. The effective radiation dose is not very high. The effective radiation dose is not very high. CT scanning is, in general, not recommended for pregnant women unless medically necessary. CT scanning is, in general, not recommended for pregnant women unless medically necessary. Children should have a CT study only if it is essential for making a diagnosis. Children should have a CT study only if it is essential for making a diagnosis. A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit for the moving table. A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit for the moving table. Soft-tissue details in areas such as the brain, internal pelvic organs, knee or shoulder can be more readily and clearly seen with MRI. Soft-tissue details in areas such as the brain, internal pelvic organs, knee or shoulder can be more readily and clearly seen with MRI.

Typical scan doses:- Examination Typical effective dose (mSv)mSv(milli rem) Chest X-ray0.110 Head CT Screening mammography 3300 Abdomen CT Chest CT Chest, Abdomen and Pelvis CT CT colonography (virtual colonoscopy) Cardiac CT angiogram Barium enema Neonatal abdominal CT202000

CT Scan image of Brain

Conclusion  Despite the rapid growth of magnetic resonance imaging (MRI) in the past decade, MRI has not superseded CT.  CT is still used routinely in radiological examinations and is, itself, undergoing rapid growth development in the form of multi-slice helical x-ray computed tomography.

References Biomedical Instrumentation: Technology and Applications by Raghbir Sing Khandpur Published by McGraw-Hill, 2004,924 pages. A. C. Kak and Malcolm Slaney, Principles of Computerized Tomographic Imaging, Society of Industrial and Applied Mathematics, 2001 Medical Devices and Systems Third edition edited by Joseph D. Bronzino COMPUTED TOMOGRAPHY: PRINCIPLES, DESIGN, ARTIFACTS AND RECENT ADVANCES. Jiang Hsieh (Editor), SPIE PRESS Monograph Vol. PM114. ISBN: COMPUTED TOMOGRAPHY : Kalendar, Willi A, Publicis MCD Varlag, Comment: Excellent technical guide to CT scanning, including multislice CT.

THANK YOU FOR YOUR ATTENTION