CT Colonography (Virtual Colonoscopy)

This page is for anyone choosing a colorectal cancer screening test. It explains CT colonography, how it compares with a standard colonoscopy, and what happens if it finds something.

This page is for people choosing a colorectal cancer screening test. It explains how CT colonography works, what to expect, and its trade-offs.

CT colonography is often called virtual colonoscopy. It screens for colorectal cancer using a CT scanner, instead of a long scope threaded through the colon. The scanner is special x-ray equipment. It takes many pictures of the colon and rectum from outside the body. A computer then builds those pictures into detailed images that can reveal polyps and other changes.

It is much less invasive than a standard colonoscopy. You don't need sedation. But there is a catch worth knowing up front. It can find polyps. It can't remove them.

A standard colonoscopy threads a long, flexible scope through the entire colon. CT colonography instead takes x-ray pictures from many angles as you lie on a table. Because the imaging happens from outside the body, only a small, soft tube is placed just inside the rectum to add air. Nothing travels up through the colon the way it does in a standard colonoscopy. That difference is what makes the test less invasive, and it is why you can skip sedation.

Even though nothing travels far up the colon, you still need a full bowel prep so the images are clear. It is the same cleaning-out process as a regular colonoscopy. For many people, that prep is the hardest part of either test.

On the day of the scan:

• A small tube is used to gently pump air into the colon to expand it
• The CT scanner takes a series of pictures
• The scan is quick, and you are awake the whole time
• No sedation means you can usually go back to normal activities right away

This is the key limitation. CT colonography can spot polyps and other abnormal growths. But it cannot remove or biopsy them. If the scan finds a polyp, you will usually need a standard colonoscopy to take it out.

That means a second appointment, and a second bowel prep. It is an important trade-off to weigh when choosing between tests.

CT colonography is one of several approved screening options for people at average risk. It may suit someone who wants to avoid sedation. It may also suit someone who prefers a test with no scope traveling through the whole colon. And it can be an option for some people who cannot have a standard colonoscopy for medical reasons.

It is not the right fit for everyone, though. If you would rather not risk needing a second test and a second prep, a standard colonoscopy may suit you better, since it can remove polyps in the same visit. Your care team can help you weigh these trade-offs against your preferences and health.

A few extra points can help you decide:

• Radiation. The scan involves a small amount of radiation, since it uses x-ray technology.
• Findings outside the colon. The scan pictures nearby organs too. So it can turn up unrelated things, some important and many harmless, that may need extra follow-up.
• Some polyps. It may be less effective than a standard colonoscopy at finding certain polyps.

For people at average risk, experts generally recommend CT colonography every 5 years. The USPSTF lists it as one screening choice for adults ages 45 to 75.

Since January 1, 2025, Medicare covers screening CT colonography. You must be 45 or older, have no symptoms and be at average risk. A treating doctor must order it. Medicare covers it once every 5 years for average risk. There is no deductible or coinsurance for the test.

Private plans may treat it differently. The test is also not available in every area.

If you are considering this test, check whether it is available nearby, and confirm coverage with your insurer first.

Some symptoms after the scan or the prep need a call. Use this list to decide how fast.

NIDDK says to get medical care right away for severe belly pain, fever, bleeding, dizziness or weakness after the test.

• Call 911 or go to an emergency department if severe pain sets in across your abdomen after the air is pumped in, or you pass blood from the anus, or you become dizzy or very weak. Do not drive yourself.
• Call your care team right away if you develop a fever after the scan, or the bloating becomes hard, painful and steadily worse instead of easing. For emergencies call 911 or go to the ER.
• Call your care team within a day or two if the bowel prep leaves you unable to keep fluids down, or you have not heard what your images showed by the date you were given.

Sources: NIDDK — Virtual Colonoscopy; CMS MLN Matters MM14031 — Updates to Colorectal Cancer Screening and Hepatitis B Vaccine Policies, accessed 2026-08-13; USPSTF — Colorectal Cancer: Screening.