Definition of CT scan:

A computed tomography (CT) scan is an imaging method that uses x-rays to create cross-sectional pictures of the body.

See also:

• Cranial CT scan
• Lumbosacral spine CT scan
• Orbit CT scan
• Thoracic CT scan

How the test is performed:

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 be still during the exam, because movement causes blurred images. You may be told to hold your breath for short periods of time.

Generally, complete scans take only a few minutes. The newest scanners can image your entire body, head to toe, in less than 30 seconds.

How to prepare for the test:

Certain exams require a special dye, called contrast, to be delivered into the 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 medications before the test in order to safely receive this substance.

Contrast can be given several ways, and depends on the type of CT being performed.

• It may be delivered through a vein (IV) in your hand or forearm.
• It may be given through the rectum using an enema.
• You might drink the contrast before your scan. When you actually drink the contrast depends on the type of exam being done. The contrast liquid may taste chalky, although some are flavored to make it taste a little better. The contrast eventually passes out of your body through your stools.

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) because you may need to take extra precautions.

If you weigh more than 300 pounds, find out if the CT machine has a weight limit. Too much weight can cause damage to the scanner's working parts.

You will be asked to remove jewelry and wear a hospital gown during the study.

How the test will feel:

Some people may have discomfort from lying on the hard table.

Contrast given through an IV may cause a slight burning sensation, 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.

Why the test is performed:

CT rapidly creates detailed pictures of the body, including the brain, chest, spine, and abdomen. The test may be used to:

• Diagnose an infection
• Guide a surgeon to the right area during a biopsy
• Identify masses and tumors, including cancer
• Study blood vessels