Alternate Names: Computerized tomography; CAT scan
How Performed: You are asked to lie on a narrow table (gantry) that slides into the center of the scanner. The scanner looks like a tube surrounded by the imaging equipment. A contrast-media (dye) may be injected into a vein to help define certain tissues. The table will advance slightly (1/4 to 1/2 inch) between each scan to align for the next cross-section image. The technologist operating the computer may indicate when it is necessary to control breathing. A sound system is built into the machine to allow communication with you during the test.
During the test, it is very important to remain still. If a patient is restless or traumatized, you may be given a sedative. Each exposure takes a few seconds. The complete scan takes about 1 hour.
How To Prepare: The health care provider may advise fasting for 4 to 6 hours if contrast dye is to be used or if sedation is anticipated (consult the health care provider). You wear a hospital gown during the procedure and asked to sign a consent form.
How It Feels: The X-rays are painless. The primary discomfort may be from the need to lie still on the table.
If a dye is needed to increase the contrast between different tissues or organs, it is administered by injection into a vein. The injection may sting and the site may be tender to the touch for several minutes. Dye injections may cause a cool or warm sensation, a metallic taste and, in a few cases, hives.
Risks: CT scans and other X-rays are monitored and regulated to provide the minimum amount of radiation exposure needed to produce the image. CT scans provide low levels of radiation. During pregnancy, an abdominal CT scan is usually not recommended, because there is some evidence of risk to the fetus.
The most common dye used is iodine based. A person who is allergic to iodine may experience nausea, sneezing, vomiting, itching, or hives. Rarely, the dye may cause anaphylaxis (a life-threatening allergic response).
For additional information regarding why the test is performed and normal and abnormal results, please see the specific CT topics:
