How CAT Scans Work

Scanning Procedure

A scanned liver slice
A scanned liver slice
Photo courtesy NASA

The CAT machine looks like a giant doughnut tipped on its side. The patient lies down on a platform, which slowly moves through the hole in the machine. The X-ray tube is mounted on a movable ring around the edges of the hole. The ring also supports an array of X-ray detectors directly opposite the X-ray tube.

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A motor turns the ring so that the X-ray tube and the X-ray detectors revolve around the body. Each full revolution scans a narrow, horizontal "slice" of the body. The control system moves the platform farther into the hole so the tube and detectors can scan the next slice.

In this way, the machine records X-ray slices across the body in a spiral motion. The computer varies the intensity of the X-rays in order to scan each type of tissue with the optimum power. After the patient passes through the machine, the computer combines all the information from each scan to form a detailed image of the body. It's not usually necessary to scan the entire body, of course. More often, doctors will scan only a small section.

Since they examine the body slice by slice, from all angles, CAT scans are much more comprehensive than conventional X-rays. Today, doctors use CAT scans to diagnose and treat a wide variety of ailments, including head trauma, cancer and osteoporosis. They are an invaluable tool in modern medicine.

For much more information about CAT scan machines and other medical scanners, check out the links below.

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