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CAT Scan/CT Scan Computed Axial Tomography Computed Tomography Ravi Ranjan

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  • 1. CAT Scan/CT ScanComputed Axial Tomography Computed TomographyRavi

2. Basic principles Mathematical principles of CT were firstdeveloped in 1917 by Radon Proved that an image of an unknown objectcould be produced if one had an infinitenumber of projections through the object 3. X-Rays photons produced by an electron beam similar to visible light, but higher energy! 4. X-Rays - Physics Associated with inner shell electrons As the electrons decelerate in the target throughinteraction, they emit electromagnetic radiationin the form of x-rays. patient between an x-ray source and a film ->radiograph cheap and relatively easy to use potentially damaging to biological tissue 5. Basic principles Plain film imaging reduces the 3D patientanatomy to a 2D projection image Density at a given point on an imagerepresents the x-ray attenuation propertieswithin the patient along a line between thex-ray focal spot and the point on thedetector corresponding to the point on theimage 6. Basic principles (cont.) With a conventional radiograph, information withrespect to the dimension parallel to the x-raybeam is lost Limitation can be overcome, to some degree, byacquiring two images at an angle of 90 degrees toone another For objects that can be identified in bothimages, the two films provide locationinformation 7. CT - basics CTs primary benefit is the ability to separateanatomical structures at different depths within thebody. A form of tomography can be performed by movingthe X-ray source and detector during an exposure. Anatomy at the target level remains sharp, whilestructures at different levels are blurred. By varying the extent and path of motion, a variety ofeffects can be obtained, with variable depth offieldand different degrees of blurring of out of planestructures. 8. CT Basics 9. CT & CATCAT stands for Computerized Axial Tomographywhich was later changer to just CT or ratherComputerized Tomography.The scanners originally only did axial images(referring to the plane of the image) but laterbecame able to do other planes such as coronalor saggital imaging and can now do anything withthe blockofinformation it collects. 10. Computed Axial Tomography Godfrey NewboldHounsfield introducedthe system to the publicin 1972 Nobel Prize in 1979 It looks like a donut Made up of a series of X- ray sources and sensors Tomogram 11. Process and Procedure X-ray + Axial view +Computer Imaging = CATScan X-ray + (digital) ComputerImaging = CT scan Provides cross-sectionalviews and images of bodyorgans and structures Pixel, Radiodensity, Voxel,Windowing Contrast Material 12. Computed Axial Tomography Also called CAT scanning or CT Image formed using a rotating thin beam(s) ofionizing radiation Image slices reconstructed by computation The image formed is related to the subjectsdensity Image display on computer or multiple films New technology is multislice helical scanner 13. CT - principle Because contemporary CT scanners offerisotropic, or near isotropic, resolution, display ofimages does not need to be restricted to theconventional axial images. Instead, it is possible for a software program tobuild a volume by stacking the individual slicesone on top of the other. The program may thendisplay the volume in an alternative manner. 14. Tomographic images The tomographic image is a picture of a slab of thepatients anatomy The 2D CT image corresponds to a 3D section of thepatient CT slice thickness is very thin (1 to 10 mm) and isapproximately uniform The 2D array of pixels in the CT image corresponds to anequal number of 3D voxels (volume elements) in thepatient Each pixel on the CT image displays the average x-rayattenuation properties of the tissue in the corrspondingvoxel 15. Tomographic acquisition Single transmission measurement through thepatient made by a single detector at a givenmoment in time is called a ray A series of rays that pass through the patient atthe same orientation is called a projection or view Two projection geometries have been used in CTimaging: Parallel beam geometry with all rays in a projection parallel to one another Fan beam geometry, in which the rays at a given projection angle diverge 16. diagnostic Uses The Head Hemorrhaging, cerebrovascular accidents, trauma The Abdomen, Pelvis, and Chest Cancers, pneumonia, infection Barium Sulfate The Spine and Bones Vertebrae, disc, spinal cord definition, and bonedensity Indicator of Osteoporosis Cardiac CT angiography. 17. CT - diagnostic useCranial diagnosis of cerebrovascular accidents and intracranial hemorrhage CT generally does not exclude infarct in the acute stage of a stroke. For detection of tumors, CT scanning with IV contrast is occasionally used but is less sensitive than magnetic resonance imaging (MRI). 18. CT - diagnostic useChestCT is excellent for detecting both acute and chronicchanges in the lung parenchyma.For evaluation of chronic interstitial processes(emphysema, fibrosis, and so forth), thin sections with highspatial frequency reconstructions are used - often scans areperformed both in inspiration and expiration. This specialtechnique is called High resolution CT (HRCT).For detection of airspace disease (such aspneumonia) or cancer, relatively thicksections and general Purpose imagereconstruction techniques may be adequate. 19. CT - diagnostic useAbdominal and pelvic CT is a sensitive method for diagnosis of abdominal diseases. Itis used frequently to determine stage of cancer and to followprogress. It is also a useful test to investigate acute abdominalpain. Renal/urinarystones, appendicitis, pancreatitis, diverticulitis, and bowelobstruction are conditions that are readily diagnosed andassessed with CT. CT is also the first line for detecting solid organ injury aftertrauma. 20. CT step by step 21. CT step by step 22. CT step by step 23. CT step by step 24. Benefits: Painless procedureother than needing greatdeal of patience Alternative to catheters and other guidecamera options A good option for those weary of enclosedspaces Usually preferred over MRI, and costs less!!! Improved technology has lead to Spiral andHelical Scansfaster processes 25. Spiral and Helical Scanners Spiral Circular Path Constant gantry rotation and readings Less exposure to radiation Faster scan = better accuracy when patientmust hold their breath 26. Potential Risks Exposure to Radiation Reduced with Spiral Scan Reaction to contrast material Diabetics Isovue Pregnant and nursing women should not beexposed 27. Investigating Emotionality and Psychopathology Dementia Anorexia Nervosa Neurological Abnormalities Schizophrenia 28. THANKS 29. CT - diagnostic useCardiac With the advent of subsecond rotation combined with multi-slice CT (up to 64-slice), high resolution and high speed can beobtained at the same time, allowing excellent imaging of thecoronary arteries (cardiac CT angiography). Images with an even higher temporal resolution can beformed using retrospective ECG gating. In this technique, eachportion of the heart is imaged more than once while an ECGtrace is recorded. The ECG is then used to correlate the CTdata with their corresponding phases of cardiac contraction.Once this correlation is complete, all data that were recordedwhile the heart was in motion (systole) can be ignored andimages can be made from the remaining data that happenedto be acquired while the heart was at rest (diastole). In thisway, individual frames in a cardiac CT investigation have abetter temporal resolution than the shortest tube rotationtime.