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tomography (to-mog´ra-fe)

Making a radiographic image of a selected plane by means of reciprocal linear or curved motion of the x-ray tube and film cassette; images of all other planes are blurred ("out of focus") by being relatively displaced on the film.conventional t., planigraphy, planography, sectional radiography, stratigraphy;
computed t. (CT) imaging anatomical information from a cross-sectional plane of the body, each image generated by a computer synthesis of x-ray transmission data obtained in many different directions in a given plane.computerized axial t; Developed in 1967 by British electronics engineer Godfrey Hounsfield, CT has revolutionized diagnostic medicine. Hounsfield linked x-ray sensors to a computer and worked out a mathematical technique called algebraic reconstruction for assembling images from transmission data. In 1973, the Mayo Clinic began operating the first machine in the U.S. Early machines yielded digital images with at least 100 times the clarity of normal x-rays. Subsequently, the speed and accuracy of machines has improved many times over. CT scans reveal both bone and soft tissues, including organs, muscles, and tumors. Image tones can be adjusted to highlight tissues of similar density, and, through graphics software, the data from multiple cross-sections can be assembled into 3-D images. CT aids diagnosis and surgery or other treatment, including radiation therapy, in which effective dosage is highly dependent on the precise density, size, and location of a tumor.
computerized axial t. (CAT) computed t
conventional t. tomography
dynamic computed t. computed t. with rapid injection of contrast medium, usually with sequential scans at only one or a few levels; used to enhance the vascular compartment.dynamic CT;
helical computed t. spiral computed t
high resolution computed t. (HRCT) computed t. with narrow collimation to reduce volume-averaging and an edge-enhancing reconstruction algorithm to sharpen the image, sometimes with a restricted field of view to minimize the size of pixels in the region imaged; used particularly for lung imaging.
hypocycloidal t. body section radiography using a complex film and tube motion with a pattern resembling a three-leaf clover.
nuclear magnetic resonance t. magnetic resonance imaging
positron emission t. (PET) tomographic images formed by computer analysis of photons detected from annihilation of positrons emitted by radionucldes incorporated into biochemical substances; the images, often quantitated with a color scale, show the uptake and distribution of the substances in the tissue, permitting analysis and localization of metabolic and physiological function.Because the half-lives of the radionuclides are so short (20 minutes to 2 hours), and the equipment expensive, PET is rarely used in a clinical setting. But since its development in the mid-1970s, it has proved the most important tool yet devised for experimental investigation of the living brain, whether healthy, traumatized, or diseased. With CT and MRI, it represents a new generation of computer imaging techniques that have revolutionized medicine and physiology.
single photon emission computed t. (SPECT) tomographic imaging of metabolic and physiological functions in tissues, the image being formed by computer synthesis of photons of a single energy emitted by radionuclides administered in suitable form to the patient.
spiral computed t. computed t. in which the x-ray tube continuously revolves around the patient, who is simultaneously moved longitudinally; computer interpolation allows reconstruction of standard transverse scans or images in any preferred plane.helical computed t., helical CT, spiral CT;
trispiral t. hypocycloidal t. that allows a much thinner and more uniform plane of focus; used especially for inner ear t.


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