CT Scan: Computed Axial Tomography (CAT) Scan


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CT Scan Machine Image by Raziel

Engineer Godfrey Hounsfield and physicist Allan Cormack invented the “computed tomography” (CT) scan. Also known as a “computed axial tomography” (CAT) scan, it allows doctors to see the soft tissues inside the body, unlike the conventional X-ray that only allows the outline of bones and organs to be seen. As it uses a computer to produce detailed cross-sectional images of the body, doctors can examine the body one narrow “slice” at a time to pinpoint specific areas of concern.

CAT Scan Inventors and Early CT Scan Machines

The CT scan was invented in 1972 by two scientists working independently. British engineer Godfrey Hounsfield of EMI laboratories invented the CT scan in England, and South African-born physicist Allan Cormack of Tufts University invented it in the United States.

The first machines were installed between 1974 and 1976, and were originally designed to scan the head of the body only. The whole-body-systems with studies became available in 1976.  Currently, an entire chest scan can be taken in 5 to 10 seconds using the most advanced multi-slice system.

Many of the improvements have been made in patient comfort, the ability to scan more anatomy in less time, and an increase in image quality. Recent researches are focused to provide excellent image quality for diagnostic confidence and the lowest possible X-ray dosage and exposure.

CT Scan Basics

A CT scan is based on X-ray principles. As X-rays pass through the body, they are absorbed at different levels, creating a matrix or profile of X-ray beams of different strengths. As the X-ray profile is registered on film, it creates an image. For a CT image, the film is replaced by a gently curved detector that measures the X-ray profile.

A CT scan looks like a large square. The opening where the patient enters is 24 to 28 inches in diameter. Inside it is a rotating frame with an X-ray tube attached on one side and the curved detector mounted on the opposite side. A fan beam of X-ray is created as the rotating frame spins the X-ray tube and detector around the patient.

With each full rotation of the detector and the X-ray tube, the detector takes many snapshots of the X-ray beam. In one full rotation, about a thousand profiles are sampled. Each profile is subdivided spatially by the detectors, fed into numerous individual channels, and reconstructed backward by a dedicated computer into a two-dimensional image of the slice that was scanned. Multiple computers are used to control the entire scan process with a “host” computer leading the entire system.

Significance of CT Scan

Through the  brilliant minds of inventors Godfrey Hounsfield and Allan Cormack, the computed axial tomography scan (CT scan) enables direct imaging and differentiation of soft tissue structures including the liver, lung tissue, and fat. It is especially useful in searching for lesions, tumors, and metastasis. The CT scan also performs imaging of the head and brain to detect tumors, blood clots, blood vessel defects and other abnormalities, including the nerves and muscles of the eye. By revealing the presence, size, spatial location and extent of the material, these high-speed and high-tech scans can provide a wealth of health information to improve your medical care.


Philbin, Tom. The 100 Greatest Inventions of All Time. New York: Citadel Press (2003)

Igbaseimokumo, Usiakimi. Brain CT Scans in Clinical Practice. New York: Springer-Verlag London Limited. (2009)

Originally published on Suite101.

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