A CAT (computed axial tomography) scan or CT scan is a noninvasive imaging  test that uses a rotating x-ray device to create detailed cross-sectional images (or slices) of different body parts. It may be performed alone or with the use of a special dye (contrast medium).

CAT scans are used to diagnose a number of injuries, conditions and diseases, including those that affect the digestive system. Some of these conditions include appendicitis, pancreatitis, gallstones and other disorders affecting the pancreas, liver, colon and rectum.

Patients are urged to follow all preparatory steps recommended by their physician prior to a CAT scan. The test is generally performed by a radiology technician in a hospital or outpatient clinic.  

If a contrast medium will be used, it can be administered orally (by mouth), through an enema or intravenously (injected into a vein) before the scan. CAT scans are typically painless. However, patients may experience a stinging sensation or slight discomfort if a contrast medium is administered intravenously. During the test, the patient lies down on a scanning table, which slides slowly into a short, open-ended tunnel.

The length of a CAT scan varies from a few minutes to an hour, depending on the type of equipment used and the requests of the physician. Patients may usually resume normal activities after the test.

In the 1990s, a new form of CAT scan was developed called a spiral CAT scan (also called a helical CAT scan or volumetric CT). These CAT scans have several advantages over earlier types. They can be used to create three-dimensional images of body areas, and can be performed in less time than earlier tests. Another type of CAT scan that is sometimes used is a combined PET/CAT scan. This combines CAT scan with another imaging procedure called positron emission tomography (PET) scan.

There are some risks associated with CAT scans. Radiation levels used with CAT scans are higher than those used with x-rays. In rare cases, the contrast medium used during a CAT scan may cause an allergic reaction. In addition, CAT scan of the chest or abdomen is not typically recommended for women who are or might be pregnant.

Unlike other types of imaging tests, such as magnetic resonance imaging (MRI), people with pacemakers or defibrillators (devices implanted in the chest to regulate the heart) can receive CAT scans without experiencing difficulties.