What Is Computer-Assisted Tomography?

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  • Written By: Kirsten C. Tynan
  • Edited By: John Allen
  • Last Modified Date: 17 June 2019
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Computer-assisted tomography is a medical diagnostic procedure that integrates multiple X-rays taken in different locations from different angles to form a three dimensional image. This procedure is commonly referred to as a CAT scan or a CT scan. It is non-invasive and painless and usually takes just a few minutes to complete. Computer-assisted tomography may be used to diagnose or assess such conditions as cancer, broken bones, blood clots, heart disease, and more.

Patient preparation for computer-assisted tomography depends on the area of the body that is to be scanned. To scan some areas effectively, a patient may need to fast before the procedure. The diagnostic facility may ask the patient to remove an article of clothing or wear a hospital gown, although this is not always necessary. All patients, however, are typically asked to remove metal items such as belt buckles or jewelry that may block the X-rays. Children who are too young to remain still through the procedure may be sedated.


Contrast solution may be administered to increase the visibility of certain parts of the body such as blood vessels or parts of the digestive tract. If the solution is consumed orally, such for a stomach image, it will typically be administered an hour or two before the scan. When injected intravenously, such as for examination of blood vessels, it may be administered just a few minutes before the exam. A barium enema would typically be administered in order to scan the intestines more effectively.

Once the patient is prepared for the exam, a technician will assist in positioning him on an examination table. This table will pass through the center of an X-ray machine called a gantry that looks like a large doughnut. The technician will leave the room to operate the machine from another room. As the scan proceeds, the patient may hear a whirring sound. An intercom system typically allows communication between technician and patient, for example, to instruct the patient to hold his breath for a few seconds.

Although computer-assisted tomography is very safe, it is not without some small risks. A CAT scan involves much more radiation than does a single X-ray, which increases a patient’s risk of developing cancer. This increased risk, however, is very small in comparison to the risk of developing cancer due to natural causes. While they rarely occur, allergic reactions to the contrast solution are also possible. They may result in symptoms such as itchiness or hives, or in extremely rare cases, they can be life-threatening.

The most common alternative types of medical scans are ultrasound and magnetic resonance imaging (MRI) procedures. An ultrasound produces an image from sound waves while an MRI produces an image from magnetic fields. Each has its limitations, however, and sometimes computer-assisted tomography is the best or only option. For example, MRI can take quite a bit more time than a CAT scan. In a trauma situation where time is of the essence, doctors might opt for computer-assisted tomography to speed diagnosis and treatment.



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