Virtual colonoscopy

A virtual colonoscopy uses computed tomography (CT) or magnetic resonance imaging (MRI) to make a three-dimensional image of the inner lining of the large intestine (colon) and rectum. It can be used to screen for precancerous and cancerous growths in the colon or rectum (colorectal cancer), such as polyps or tumors.

Virtual colonoscopy is one of many tests that may be used to screen for colorectal cancer. Which screening test you choose depends on your risk and what you prefer. Talk to your doctor about what puts you at risk and what test is best for you.

A virtual colonoscopy may be done to:

• Screen for colorectal cancer or polyps.
• Monitor the growth of polyps.
• Screen for recurrence of colorectal cancer in people who have had surgery for this disease.
• Replace a regular colonoscopy if the thin lighted scope can't be inserted in the colon for some reason. For instance, it may be done when a tumor blocks the passage.

Virtual colonoscopy is usually done in the radiology department at a hospital or medical center. The test is most often done by a doctor who specializes in performing and interpreting diagnostic imaging tests (radiologist). The doctor may also have an assistant.

You will need to take off most of your clothes. You'll get a gown to wear during the test.

First, you will be asked to lie on your back on the table of the CT or MRI machine. A thin tube is put into your rectum through your anus. For CT, air or carbon dioxide gas will be pumped through the tube. (There may be some discomfort as the gas expands your colon.) For MRI, a contrast liquid will be given through the tube into the colon. This helps the doctor see all parts of your colon.

The table will slide into the CT or MRI machine so pictures of your colon can be taken. You may be asked to hold your breath when pictures are taken. This can help prevent blurry pictures. Then the procedure will be repeated while you lie facedown.

Virtual colonoscopy requires the same cleansing bowel prep as a regular colonoscopy.

If you are having virtual colonoscopy using computed tomography (CT), you will be given some liquid to drink after your bowel prep. This drink is a contrast medium. It makes the large intestine easier to see in the pictures.

• Follow your doctor's directions about when to stop eating solid foods and drink only clear liquids. You can drink water, clear juices, clear broths, flavored ice pops, and gelatin (such as Jell-O).
• Take the bowel prep as your doctor tells you. You will want to stay home, because the prep will make you go to the bathroom a lot. Your stools will be loose and watery. It's very important to take all of the prep. If you have problems taking it, call your doctor.
• Do not eat any solid foods after you take the bowel prep.
• Stop drinking clear liquids for a few hours before the test. Your doctor will tell you how many hours this will be.

A negative result means that your colon appears normal. A positive result means that abnormal tissue, like a polyp, was seen. With a positive result, you'll need a colonoscopy to remove the polyp or take a tissue sample. Also, if the images show a possible problem outside the colon, you'll need more tests.