Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Computed tomography, also called CT or CT scan, is a process that uses X-rays and computer technology to make cross-sectional images of the body. A series of X-ray pictures, each a thin slice, are put together in a computer to form a three-dimensional view of the inside of your body. If an X-ray is like looking at a photo of a heart, a CT scan is like looking at a model that you can pick up and examine from any angle.

In a CT scan, X-rays pass through the body and are analyzed by a computer. The computer builds an image based on the amount of X-rays passing through tissues of different thickness. For example, bone appears white on a CT scan, and gas bubbles in the stomach and intestines appear black.

You can have a CT scan in an outpatient facility or in a hospital. The procedure is painless and takes about 20 minutes, but can be longer or shorter depending on the area of the body being scanned.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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