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

CAT scans are used to diagnose different types of injuries, conditions and diseases, including many neurological conditions. Disorders of the brain and spinal cord that can be diagnosed using a CAT scan include:

• Brain trauma, tumors and cysts
• Encephalitis
• Enlarged ventricles associated with hydrocephalus
• Some causes of epilepsy
• Herniated discs
• Spinal stenosis
• Signs of stroke, including dead brain tissue, blood clots and bleeding

CAT scans are generally performed by a radiology technician in a hospital or outpatient clinic. During the test, the patient lies down on a scanning table, which slides slowly into a short, open-ended tunnel. If a contrast medium is used, it can be administered orally (by mouth), through an enema (via the rectum) or injected into a vein. The test is painless except for brief discomfort that may be felt if an injection is used.

The length of a CAT scan can vary from a few minutes to an hour, depending on the type of equipment used and the area to be scanned. Patients will need to remain still for most of the time during a CAT scan. Patients can usually return to normal activities after the CAT scan is completed.

CAT scans are generally safe, but they may carry some risks. Radiation levels used with CAT scans are higher than those used with x-rays. In addition, the contrast medium used during a CAT scan may cause an allergic reaction in rare cases.