Tomography achieves this remarkable result by simply moving an x-ray source in one direction as the x-ray film is moved in the opposite direction during the exposure to sharpen structures in the focal plane, while structures in other planes appear blurred.
The tomogram is the picture; the tomograph is the apparatus; and tomography is the process.
2. A computerized axial tomography scan which is an x-ray procedure that combines many x-ray images with the aid of a computer to generate cross-sectional views and, if needed, three-dimensional images of the internal organs and structures of the body.
Computerized axial tomography is more commonly known by its abbreviated names, CT scan or CAT scan. A CT scan is used to define normal and abnormal structures in the body and/or to assist in procedures by helping to accurately guide the placement of instruments or treatments.
The procedure was used first in 1972 to study the brain and is a painless and noninvasive procedure that does not require any special preparation. It is considered to be 100 times more sensitive than conventional radiography or X-rays.
As well as being essential for the study of the brain, CT scanning is considered to be invaluable in investigating diseases of any part of the body. It is particularly useful for locating and imaging tumors, and for guiding the operator who is performing a needle biopsy.
Tomography achieves this result by simply moving an x-ray source in one direction as the x-ray film is moved in the opposite direction during the exposure to sharpen structures in the focal plane, while structures in other planes appear blurred.
The tomogram is the picture; the tomograph is the apparatus; and tomography is the process.
The computerized axial tomography (CAT) scan can reveal some soft-tissue and other structures that cannot even 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 five or ten millimeters (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.
CT stands for computerized tomography.