A CT scan — also called computerized tomography or just CT — is an X-ray technique that produces images of your body that visualize internal structures in cross section rather than the overlapping images typically produced by conventional X-ray exams.

Conventional X-ray exams use a stationary X-ray machine to focus beams of radiation on a particular area of your body to produce two-dimensional images on film or a digital detector, much like a photograph. But CT scans use an X-ray unit that rotates around your body and a powerful computer. The result with CT scans is a set of cross-sectional images, like slices, of the inside of your body. Doctors recommend a CT scan for a wide variety of reasons.

A conventional X-ray of your abdomen, for example, shows your bones as well as subtle overlapping outlines of your liver, stomach, intestines, kidney and spleen. A CT scan, however, clearly reveals these bones and organs as well as their inner structure and detailed anatomy of your pancreas, adrenal glands, kidneys and blood vessels.

Your doctor may recommend a CT scan to help:

• Diagnose muscle and bone disorders, such as bone tumors and fractures
• Pinpoint the location of a tumor, infection or blood clot
• Guide procedures such as surgery, biopsy and radiation therapy
• Detect and monitor diseases such as cancer or heart disease
• Detect internal injuries and internal bleeding

CT scan risks are similar to those of conventional X-rays. During the CT scan, you're briefly exposed to radiation. But doctors and other scientists believe that CT scans provide enough valuable information to outweigh the associated risks. Be sure to inform your doctor if:

You have certain medical conditions. Diabetes, asthma, heart disease, kidney problems or certain thyroid conditions may increase your risk of a reaction to contrast media.

How you prepare for a CT scan depends on which part of your body is being scanned. You may be asked to remove your clothing and wear a hospital gown. You'll need to remove any metal objects, such as jewelry, that might interfere with image results.

Preparation sometimes involves fasting
Some CT scans require you to drink a contrast liquid before the scan or have contrast injected into a vein in your arm during the scan. A contrast medium blocks X-rays and appears white on images, which can help emphasize blood vessels, bowel or other structures. If your test involves a contrast medium, your doctor may ask you to fast for a few hours before the test.

Depending on the part of your body being scanned, your doctor may ask you to take laxatives, enemas or suppositories, or temporarily modify your diet.

Reactions to contrast medium
Although rare, the contrast medium involved in a CT scan poses a slight risk of allergic reaction. Most reactions are mild and result in hives or itchiness. For people with asthma who become allergic to the contrast medium, the reaction can be an asthma attack.

Preparing your small child for a scan
If your infant or toddler is having the CT scan, the doctor may give your child a sedative to keep him or her calm and still. Movement blurs the images and may lead to incorrect results. Ask your doctor how best to prepare your child.

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