What Is a 'Virtual' Colonoscopy?

This test helps your doctor see inside your rectum and colon (also called your large intestine). You might hear her call it CT colonography, or computed tomography, a kind of test that takes pictures of your insides. It’s most often used to look for small growths called polyps and to check for colon or rectal (colorectal) cancer.

How Is It Different From a Full Colonoscopy?

During a full colonoscopy, your doctor slides a thin, flexible tube into your rectum so she can see your colon. You’ll be asleep during the process. She’ll use the light and camera on the end of the tube to look at the lining of your intestine. If she sees polyps or changes in the tissue, she can take some out through the tube and check it for cancer.

Your doctor doesn’t put a camera into your intestine for a CT colonography. You aren’t asleep during the test. Instead, she uses a CT scanner and X-rays to make 3-D pictures of your intestine on a computer screen.

Is the Prep the Same?

Pretty much. You may have to change what you eat for a few days and take medicine to clean out your colon.

You’ll need to drink a special contrast liquid before the test. It lines the inside of your intestine and makes it easier to see on the scans.

Make sure your doctor knows about all of the medicine you take. That includes drugs you can get without a prescription, like vitamins, supplements, and herbs. She may ask you to stop some of these for a short time before the test.

Tell your doctor if you’ve had past reactions to the contrast liquid used during X-rays.

Don’t get this test if you’re pregnant.

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What Happens?

A trained technician will do the test. You won’t need to stay in the hospital for it.

You’ll lie on a narrow table. First, you’ll be on your side while she puts a short, thin tube into your rectum to fill your intestine with air. This helps expand and smooth it out. It may make your belly feel full, but it shouldn’t hurt.

After the air is in, the table will slide into a big, doughnut-shaped ring. The technician will leave the room, but she will be able to see, hear, and talk to you the entire time.

She may ask you to turn or hold your breath at different times. The machine may click and whir as the scans are done. The whole thing should take 10 to 15 minutes.

How Will I Feel Afterward?

You may feel bloated for a while and have gas as you pass the air out of your intestine. You can go back to your normal diet. There are no activity limits.

You doctor will let you know when and how you’ll get the test results.

Why Aren’t All Colon Cancer Tests Done This Way?

Virtual colonoscopy has pros and cons:

Pros:

  • Fewer risks, compared with regular colonoscopy
  • It’s easier if you’re elderly or take blood thinners.
  • There’s no recovery time. You can go right back to your normal life.
  • It costs less and is faster than the regular test.

Cons:

  • Your doctor isn’t looking right at your colon and might miss small changes.
  • Insurance doesn’t always cover it.
  • It’s low, but there is radiation exposure.
  • If the test results show changes, you’ll have to come back for a regular colonoscopy so the doctor can remove and test the tissue.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on February 15, 2018

Sources

SOURCES:

Radiological Society of North America: “CT Colonography.”

National Institute of Diabetes and Digestive and Kidney Diseases: “Virtual Colonoscopy.”

Johns Hopkins Medicine: “Virtual Colonoscopy for Cancer Screening.”

National Cancer Institute: “Computed Tomography (CT) Scans and Cancer,” “Virtual Colonoscopy.”

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