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A computed tomography (CT) scan is an imaging method that uses x-rays to create pictures of cross-sections of the body.
Related tests include:
CAT scan; Computed axial tomography scan; Computed tomography scan
You will be asked to lie on a narrow table that slides into the center of the CT scanner.
Once you are inside the scanner, the machine's x-ray beam rotates around you. Modern "spiral" scanners can perform the exam without stopping.
A computer creates separate images of the body area, called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of the body area can be created by stacking the slices together.
You must stay still during the exam, because movement causes blurred images. You may be told to hold your breath for short periods of time.
Complete scans usually take only a few minutes. The newest scanners can image your entire body in less than 30 seconds.
Certain exams require a special dye, called contrast, to be delivered into your body before the test starts. Contrast helps certain areas show up better on the x-rays.
Let your doctor know if you have ever had a reaction to contrast. You may need to take medicines before the test in order to avoid another reaction.
Contrast can be given several ways, and depends on the type of CT being performed.
If contrast is used, you may also be asked not to eat or drink anything for 4-6 hours before the test.
Before receiving the contrast, tell your health care provider if you take the diabetes medication metformin (Glucophage). People taking this medicine may need to stop temporarily.
Find out if the CT machine has a weight limit if you weigh more than 300 pounds. Too much weight can cause damage to the scanner.
You will need to remove jewelry and wear a hospital gown during the study.
Some people may have discomfort from lying on the hard table.
Contrast given through an IV may cause a slight burning feeling, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.
A CT scan creates detailed pictures of the body, including the brain, chest, spine, and abdomen. The test may be used to:
Results are considered normal if the organs and structures being examined are normal in appearance.
Abnormal results depend on the part of the body being studied. Talk to your health care provider about questions and concerns.
Risks of CT scans include:
CT scans expose you to more radiation than regular x-rays. Having many x-rays or CT scans over time may increase your risk for cancer. However, the risk from any one scan is small. You and your doctor should weigh this risk against the value of the information that will come from a CT scan.
Some people have allergies to contrast dye. Let your doctor know if you have ever had an allergic reaction to injected contrast dye.
Rarely, the dye may cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, tell the scanner operator immediately. Scanners come with an intercom and speakers, so the operator can hear you at all times.
Shaw AS, Dixon AK. Multidetector computed tomography. In: Adam A, Dixon AK, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 4.
Review Date: 11/9/2012
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.
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