Axial tomography, computerized: 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.
Axillary: Pertaining to the armpit, the cavity beneath the junction of the arm and the body.
- Axillary dissection
Axillary dissection: Removal of a portion of the lymph nodes under the arm.
- Axillary hyperhidrosis
Excessive sweating from the armpits. Excessive underarm perspiration tends to start in late adolescence.
Axis: The axis is the second cervical vertebra (symbol: C2). It is called the “axis” because the uppermost cervical vertebra (called the atlas) rotates about the odontoid process of C2. The joint between the axis and atlas is a pivot type of joint. It allows the head turn. The Latin word “axis” means axle or […]
Axon: A long fiber of a nerve cell (a neuron) that acts somewhat like a fiber-optic cable carrying outgoing (efferent) messages. The neuron sends electrical impulses from its cell body through the axon to target cells. Each nerve cell has one axon. An axon can be over 20 cm (a foot) in length, which for […]