CT Colonography (Virtual Colonoscopy)

A CT scan is a test that combines X-rays and computer scans. A CT colonography is used to view the inside of your lower digestive tract (colon and rectum). It can help screen for colon cancer and for polyps (small growths in the colon that can become cancer). This test is sometimes called virtual colonoscopy. In some cases, this test may be done instead of regular colonoscopy for colon cancer screening. Both tests require a bowel prep, but regular colonoscopy also requires sedation. No sedation is needed for CT colonography. However, unlike regular colonoscopy, no biopsy or treatment can be done during the CT colonography. If a problem is found that needs further examination or treatment, a regular colonoscopy may be required.

Man lying on back on scanner table. Health care provider preparing to slide table into ring-shaped CT scanner.

Risks and possible complications of CT colonography

  • Exposure to radiation

  • Bowel perforation (hole) from gas pumped in through the rectum 

  • Failure to detect small polyps 

Before the test

  • Tell your doctor what medicine you take. This includes vitamins, herbs, and over-the-counter medicines such as aspirin. You may need to stop taking certain medicines before the test.

  • Your kidney function may be tested. This is to be sure your kidneys are working well. If they are not, this test may not be safe for you.

  • For the test, your rectum and colon must be empty of stool. You will be given bowel prep instructions. Follow these carefully. For up to 48 hours before the test, you may need to restrict what you eat and drink. You will also need to take pills or drink a liquid to cleanse your bowel of stool.

  • Be sure to arrive on time at the facility. Bring your health insurance card. Leave valuables at home. Also, remove any metal piercings, such as a belly button ring or stud, before leaving home. Metal interferes with X-rays.

  • At the hospital, you will be asked to sign a consent form. You will change into a hospital gown.

  • Follow any instructions given by your doctor or the technologist.

Let the technologist know

For your safety, tell the technologist if you:

  • Have any known kidney problems

  • Have had a reaction to IV contrast in the past

  • Are pregnant or think you may be pregnant. The radiation from a CT scanner can harm an unborn child. If you think you may be pregnant, you should not have a CT colonography

  • Ate or drank anything before the test

  • Are currently being treated for or have any form of colitis or diverticulitis including Crohn’s disease or ulcerative colitis

During the test

A CT colonography is done in a hospital or radiology center. The procedure itself takes less than 15 minutes. You can go home soon afterward. A CT scanner, is used. This is a large, donut-shaped machine. An examination table slides in and out of the hole in the center of the machine.

  • The technologist will have you lie on your back, on your side, or on your stomach on the exam table.

  • An IV line may be put into a vein in your arm or hand. This line gives you fluids and medicine. You may be given a medicine through the IV to help prevent cramping.

  • You may be given contrast fluid. This fluid helps the rectum and colon show up more clearly on the X-rays. The fluid may be put through the IV. You may drink the contrast. Or the contrast may be put directly into your rectum and colon. The technologist can tell you more about this.

  • A slender tube is put about 2 inches into your rectum. Carbon dioxide gas or room air  is pumped through the tube. This inflates the colon enough so the CT scanner can have a better image of the inside of the colon. You may feel some discomfort and fullness from the gas.

  • The technologist will go into a separate room, but he or she will still be able to talk to you and hear you.

  • The exam table slides you into the CT scanner tunnel. The scanner takes X-rays of your body. You need to lie very still. You may be asked to hold your breath for a short time during the scan. This helps get the clearest picture.

  • The exam table then slides out of the tunnel.

  • Then you may be asked to lie on your stomach or on your side to repeat the procedure.

After the test

  • You can eat and drink normally as soon as the test is done.

  • You will likely pass a lot of gas after the procedure. This is normal.

When to call your health care provider

Call your doctor if you notice any of the following:

  • Fever of 100.4°F (38.0°C) or higher

  • Fever (1°F above your normal temperature) lasting for 24 to 48 hours

  • Or, whatever your health care provider told you to report based on your medical condition

  • Pain in the lower abdomen that worsens or does not go away within 24 hours


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