Medical Definition of Ct scan
A special radiographic technique that uses a computer to assimilate multiple X-ray images into a 2 dimentional cross-sectional image.
This can reveal many soft tissue structures not shown by conventional radiography. Scans may also be dynamic in which a movement of a dye is tracked. Cuts may be 5 or 10 mm apart or, in some instances even further apart. A special dye material may be injected into the patients vein prior to the scan to help differentiate abnormal tissue and vasculature.
The machine rotates 180ø around the patients body, sending out a pencil-thin X-ray beam at 160 different points. Crystals positioned at the opposite points of the beam pick up and record the absorption rates of the varying thicknesses of tissue and bone. These data are then relayed to a computer that turns the information into a picture on a screen. Using the same dosage of radiation as that of the conventional X-ray machine, an entire slice of the body is made visible with about 100 times more clarity.
The scanner was invented in 1972 by the British electronics engineer Godfrey N. Hounsfield and was in general use by 1979.
Synonym: computerised axial tomography.
(15 Nov 1997)
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