CT colonography

What is a CT colonography?

CT (computerised tomography) colonography is a newer test that is also called virtual colonoscopy.

If you need a CT colonography, you may have to travel to a specialist centre. Your doctor or nurse can give you more information about this test.

Instead of having a colonoscope put into your bowel, a computer uses CT scanning images to examine your bowel. A CT scan takes a series of x-rays, which builds up a three-dimensional picture of the inside of the body. The CT scan uses a small amount of radiation, which is very unlikely to harm you and won’t harm anyone you come into contact with.

In this test, a CT scanner takes a series of x-ray pictures of your bowel. A computer then puts the pictures together to make a three-dimensional picture of your bowel. This test may be done instead of a colonoscopy, or it may be done if the colonoscopy didn’t give a clear enough picture.

A virtual colonoscopy is done in the hospital CT department. You can usually have it as an outpatient.

Your bowel has to be completely empty for the scan. You’ll need to follow a special diet for a few days and take a laxative before the test. Your hospital will give you instructions about what to do.

Your doctor may give you an injection of a medicine to help the muscles in your bowel relax. You may also have an injection of a dye (contrast medium) at the same time. Your doctor will tell you if you’re going to have this.

Just before the CT scan, the doctor will pass a tube into your back passage (rectum) and pump in some air and gas (carbon dioxide). This expands the bowel and helps to give a clearer picture. You will have two CT scans – one while lying on your back and one while lying on your front.

Waiting for test results

Waiting for test results can be a difficult time. It may take from a few days to a couple of weeks for the results of your tests to be ready. You may find it helpful to talk with your partner, family or a close friend. Your specialist nurse or one of these organisations can also provide support.

You can also talk things over with one of our cancer support specialists on 0808 808 00 00.

Back to Bowel screening

The bowel

The bowel is part of our digestive system and is made up of the small bowel and the large bowel.

What is bowel cancer screening?

Bowel screening can find bowel cancer at a very early stage, when it has the best chance of being treated.

What to do with your FOB test kit

This test checks bowel motions for tiny amount of ‘hidden blood’. It is not a test for cancer, but can indicate whether further tests are needed to examine the bowel.

Getting your FOB test results

Waiting for your FOB test results can be an anxious time. You should get them back within two weeks.

Your feelings about bowel screening

People react differently to their bowel screening results. There is no right or wrong way to feel.


A colonoscopy is a way of examining the lining of the bowel from the inside.

Barium enema

This is a special x-ray of the large bowel.

Common questions about bowel screening

You may have lots of questions about bowel screening. You can ask your GP if you’re unsure of anything.