Computerized axial tomography scan: Pictures of structures within the body created by a computer that takes the data from multiple X-ray images and turns them in pictures. The CAT (computerized axial tomography) scan can reveal some soft-tissue and other structures that cannot be seen in conventional X-rays. Using the same dosage of radiation as that of an ordinary X-ray machine, an entire slice of the body can be made visible with about 100 times more clarity with the CAT scan.

The "cuts"(tomograms) for the CAT scan are usually made 5 or 10 mm apart. The CAT machine rotates 180 degrees around the patient's body; hence, the term "axial." The machine sends out a 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. The data are then relayed to a computer that turns the information into a 2-dimensional cross-sectional image.

CAT scanning was invented in 1972 by the British engineer Godfrey N. Hounsfield (later Sir Godfrey) and the South African (later American) physicist Alan Cormack. CAT scanning was already in general use by 1979, the year Hounsfield and Cormack were awarded the Nobel Prize in Medicine or Physiology for its development.

The CAT scan is also known as the CT (computerized tomography) scan.