The short answer
CT colonography, also called virtual colonoscopy, uses a CT scanner to take detailed pictures of the colon and rectum from outside the body. It still needs a bowel prep but no sedation. If it finds polyps, a regular colonoscopy is usually needed to remove them.
CT colonography uses a CT scanner to picture the colon from outside the body — no scope is inserted far into the colon.
You still need a full bowel prep, but you don't need sedation.
It is usually repeated every 5 years for people at average risk.
If polyps are found, you'll usually need a regular colonoscopy to remove them.
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The full explanation.
The simple version
CT colonography — often called virtual colonoscopy — screens for colorectal cancer using a CT scanner instead of a long scope threaded through the colon. The scanner is special x-ray equipment that 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 understanding up front: it can find polyps, but it can't remove them.
Virtual colonoscopy pictures the colon from outside the body — no sedation, but no polyp removal either.
How it works
Instead of threading a long, flexible scope through the entire colon, CT colonography uses a CT scanner — 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.
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 lets you skip sedation.
The scan builds a detailed picture of the colon from x-rays taken outside the body.
What to expect
Even though nothing travels far up the colon, you still need a full bowel prep so the images are clear — 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.
If polyps are found
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.
Who might choose it
CT colonography is one of several approved screening options for people at average risk. It may appeal to someone who wants to avoid sedation, or who prefers a test that doesn't involve a scope traveling through the whole colon. It can also 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 — which can remove polyps in the same visit — may suit you better. 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.
Other things to know
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.
How often, cost, and access
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 — but virtual colonoscopy is an exception in some cases. Medicare and some insurers currently do not pay for it, and it is not available in every area.
If you are 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.
Words to know
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Common questions
▸What is virtual colonoscopy?
Virtual colonoscopy is another name for CT colonography. It uses a CT scanner — special x-ray equipment — to take a series of pictures of the colon and rectum from outside the body. A computer combines them into detailed images that can show polyps and other changes, without threading a scope through the whole colon.
▸Do I still need the bowel prep?
Yes. As with a standard colonoscopy, your colon must be thoroughly cleaned out beforehand so the images are clear. That prep is often the least pleasant part. The main difference is that you don't need sedation for CT colonography.
▸What happens during the scan?
A little air is gently pumped into the colon through a small tube to expand it, then the CT scanner takes pictures. The scan is quick and minimally invasive. You are awake the whole time and can usually go about your day afterward.
▸What if it finds a polyp?
CT colonography can find polyps, but it cannot remove them. If polyps or other abnormal growths are found, you will usually need a standard colonoscopy to take them out. That means a second prep and visit, which is worth knowing before you choose this test.
▸How often would I need it?
Experts generally recommend CT colonography every 5 years for people at average risk. Your care team can tell you whether this interval and this test are right for your situation.
▸Are there downsides?
It involves a small amount of radiation, and because it also pictures areas outside the colon, it can find unrelated things that need extra follow-up. It may also miss very small polyps. And it is not available everywhere and may not be covered by all insurance plans.
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