CT Colonography (Virtual Colonoscopy)

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, and you don't need sedation. But there is a catch worth knowing up front. It can find polyps. It can't remove them.

Virtual colonoscopy pictures the colon from outside the body — no sedation, but no polyp removal either.

A standard colonoscopy threads a long, flexible scope through the entire colon. CT colonography uses a CT scanner instead — the same kind of machine used for many other medical scans. It takes many x-ray pictures from different angles as you lie on a table. A computer then stitches those pictures together into detailed cross-section images of the colon and rectum.

The imaging happens from outside the body. So 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.

The scan builds a detailed picture of the colon from x-rays taken outside the body.

Nothing travels far up the colon. Even so, 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 drive yourself home

You'll still do the full prep, but you'll skip the sedation and recovery time.

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.

A positive CT colonography usually leads to a standard colonoscopy, so plan for that possibility.

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. Would you rather not risk needing a second test and a second prep? Then 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.

CT colonography suits people who want to avoid sedation, but plan for a possible follow-up colonoscopy.

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. Because the scan pictures nearby organs too, it can turn up unrelated things — some important, many harmless — that may need extra follow-up.
• Small polyps. Very small polyps can be missed, though many small polyps are unlikely to become cancer.

For people at average risk, experts generally recommend CT colonography every 5 years. Colorectal cancer screening is a preventive service that many plans are required to help cover. Medicare began paying for screening CT colonography on January 1, 2025, for people aged 45 and over who have no symptoms and are at average risk. Some private plans still treat it differently from a standard colonoscopy, and the test is not available in every area.

Are you considering this test? Check availability nearby, and confirm coverage with your insurer first.

Confirm both availability and insurance coverage before choosing CT colonography — it isn't covered everywhere.

• 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.
• Call your care team the same day if you develop a fever after the scan, or the bloating becomes hard, painful and steadily worse instead of easing.
• 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.