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COMPUTED TOMOGRAPHY - CT SCAN PowerPoint Presentation

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Description : Check out this medical presentation on Radiology and Imaging, which is titled "COMPUTED TOMOGRAPHY - CT SCAN", to know about Computer tomography (CT), originally known as computed axial tomography (CAT or CT scan) and body section rentenography.

Tags : Radiology, Imaging, Computer tomography, CT, computed axial tomography, CAT, CT scan, body section rentenography

Published on : Aug 02, 2021 | Views : 8770 | Downloads : 44

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Slide 1-

COMPUTED TOMOGRAPHY CT SCAN BY SAJID EJAZ
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INTRODUCTION Computer tomography (CT), originally known as computed axial computed axial tomography (CAT or CT scan) and body section rentenography. It is a medical imaging method employing tomography where digital geometry processing is used to generate a three- dimensional image of the internals of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation.
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 The word "tomography" is derived from the Greek tomos (slice) and graphein (to write). CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various structures based on their ability to block the Xray beam.
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HISTORY The first commercially viable CT scanner was invented by Godfrey Newbold Hounsfield in Hayes, England at Thorn EMI Central Research Laboratories using X-rays. Hounsfield conceived his idea in 1967, and it was publicly announced in 1972. It is claimed that the CT scanner was "the greatest legacy" of the Beatles; the massive profits from their record sales enabled EMI to fund scientific research.
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ADVANTAGE OF COMPUTED TOMOGRAPHY OVER CONVENTIONAL RADIOGRAPHY To overcome superimposition of structures. To improve contrast of the image. To measure small differences in tissue contrast.
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PRINCIPLE OF TOMOGRAPHY The internal structure of the object can be reconstructed from multiple projections of the object. Mathematically principle of CT was first developed in 1917 by Radon. Proved that image of unknown object could be produced if one had several number of projections throughout the object.
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VARIOUS PARAMETER OF CT SLICE MATRIX PIXEL VOXEL CT NUMBER WINDOWING WINDOW WIDTH WINDOW LEVEL PITCH
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SLICE/CUT    The cross section portion of body which is scanned for production of CT image is called Slice. The slice has width and therefore volume. The width is determined by width of the x rays beam.
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MATRIX The CT image is represented as the Matrix of the number. A two dimensional array of numbers arranged in rows and columns is called Matrix. Each number represent the value of the image at that location.
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PIXEL Each square in a matrix is called a pixel. Also known as picture element. VOXEL Each individual element or number in the image matrix represents a three dimensional volume element in object called VOXEL.
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CT NUMBER The numbers in the image matrix is called CT NUMBER. Each pixel has a number which represents the x-ray attenuation in the corresponding voxel of the object.
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HOUNSFIELD UNIT (HU) Related to different composition and nature of Tissue. The CT NUMBER is also known as Hounsfield units(HU). Represent the density of tissue. Different Tissue have different CT number Range in HU.
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WINDOWING It is a system where the CT no. range of interest is spread cover the full grey scale available on the display system. WINDOW WIDTH –Means total range of CT no. values selected for gray scale interpretation. It corresponds to contrast of the image. WINDOW LEVEL– represents the CT no. selected for the centre of the range of the no. displayed on the image. It corresponds to brightness of image .
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PITCH The relationship between patient and tube motion is called Pitch. It is defined as table movement during each revolution of x-ray tube divided by collimation width. For example: For a 5mm section, if patient moves 10mm during the time it takes for the x- ray tube to rotate through 360˚, the pitch is 2. Increasing pitch reduces the scan time and patient dose.
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GENERATION OF CT First Generation:- Narrow pencil beam Single detector Detector used is made up of NaI. Translate –Rotate movements of Tube- detector combination Scan time-5mins. Designed only for evaluation of brain.
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FIRST GENERATION CT SCAN Head kept enclosed in a water bath Paired detectors  A reference detector
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SECOND GENERATION OF CT SCAN  Narrow fan beam  Linear detector array(5 to30) Translate-Rotate movements of Tube-Detector combination Fewer linear movements are needed as there are more detectors to gather the data. Between linear movements, the gantry rotated 30o Scan time~30secs(advantage over first generation)
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THIRD GENERATION OF CT SCAN Rotate(tube)Rotate(detectors) Motion. Pulsed wide fan beam. Arc of detectors(600-900) Detectors are perfectly aligned with the X-Ray tube Both Xenon and scintillation crystal detectors can be used Scan time< 5secs Disadvantage: Ring Artifacts due to electronic drift between many detectors.
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THIRD GENERATION OF CT SCAN
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FOURTH GENERATION OF CT SCAN Complete circular array of about 1200 to 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 or, <2s. Designed to address ring artifacts by keeping detector assembly stationary. Disadvantage: High cost.
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FOURTH GENERATION OF CT SCAN
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FIFTH GENERATION OF CT SCAN Stationary/stationary Developed specifically for cardiac tomographic imaging No conventional x-ray tube; large arc of tungsten encircles patient and lies directly opposite to the detector ring Electron beam steered around the patient to strike the annular tungsten target Capable of 50-msec scan times; can produce fast- frame- rate CT movies of the beating heart.
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FIFTH GENERATION OF CT SCAN
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CT BASIC ARDWARE A-X-ray tube B-Collimators C-Detectors – Scintillation crystals -Xenon gas ionisation chambers -Ceramic scintillators
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X-RAY TUBE • • Focal spot:0.6mm Annode heat capacity
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TWO COLLIMATORS IN CT PREPATIENT COLIIMATORS • • Determine slice thickness Reduce patient dose • • PREDECTOR COLLIMATORS Reduce scattered radiation to improve contrast Helps determine slice thickness
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Thank you…