N: 1. – CAT (acron): 1975, medical acronym for computerized axial tomography or something like it. Related: CAT scan.
– scan (n): 1706, “close investigation,” from scan (v.). Meaning “act of scanning” is from 1937; sense of “image obtained by scanning” is from 1953.
2. A procedure that uses a computer linked to an x-ray machine to make a series of detailed pictures of areas inside the body. The pictures are taken from different angles and are used to create 3-dimensional (3-D) views of tissues and organs. A dye may be injected into a vein or swallowed to help the tissues and organs show up more clearly. A CAT scan may be used to help diagnose disease, plan treatment, or find out how well treatment is working. Also called computed tomography scan, computerized axial tomography scan, computerized tomography, and CT scan.
3. The term “computed tomography”, or CT, refers to a computerized x-ray imaging procedure in which a narrow beam of x-rays is aimed at a patient and quickly rotated around the body, producing signals that are processed by the machine’s computer to generate cross-sectional images—or “slices”—of the body. These slices are called tomographic images and contain more detailed information than conventional x-rays. Once a number of successive slices are collected by the machine’s computer, they can be digitally “stacked” together to form a three-dimensional image of the patient that allows for easier identification and location of basic structures as well as possible tumors or abnormalities.
Unlike a conventional x-ray—which uses a fixed x-ray tube—a CT scanner uses a motorized x-ray source that rotates around the circular opening of a donut-shaped structure called a gantry. During a CT scan, the patient lies on a bed that slowly moves through the gantry while the x-ray tube rotates around the patient, shooting narrow beams of x-rays through the body. Instead of film, CT scanners use special digital x-ray detectors, which are located directly opposite the x-ray source. As the x-rays leave the patient, they are picked up by the detectors and transmitted to a computer.
Each time the x-ray source completes one full rotation, the CT computer uses sophisticated mathematical techniques to construct a 2D image slice of the patient. The thickness of the tissue represented in each image slice can vary depending on the CT machine used, but usually ranges from 1-10 millimeters. When a full slice is completed, the image is stored and the motorized bed is moved forward incrementally into the gantry. The x-ray scanning process is then repeated to produce another image slice. This process continues until the desired number of slices is collected.
4. As the x-ray tube and detector make this 360° rotation, the detector takes numerous snapshots (called profiles) of the attenuated x-ray beam. Typically, in one 360° lap, about 1,000 profiles are sampled. Each profile is subdivided spatially (divided into partitions) by the detectors and fed into about 700 individual channels. Each profile is then backwards reconstructed (or “back projected”) by a dedicated computer into a two-dimensional image of the “slice” that was scanned.
S: 1. OED – http://bit.do/eAWLo; https://bit.ly/2OQZhyu (last access: 17 November 2018). 2. NCI – http://bit.do/eAWLL (last access: 15 November 2018). 3. NIBIB – http://bit.do/eAWN5 (last access: 15 November 2018). 4. TERMIUM PLUS – https://bit.ly/2BdE1PW (last access 17 November 2018).
SYN: computed tomography, CT, computed axial tomography scan, computerized tomography, computed axial tomography, CAT, computed tomography scan, CT scan, computerized axial tomography, computerised tomography scan, computer-assisted tomography, computer-aided tomography, computerized transaxial tomography, CTT (less frequent), computerized transverse axial tomography, computer-assisted axial tomography.