Virtual Colonoscopy

Why have a virtual colonoscopy?

Virtual colonoscopy (also called a computerised tomography colonography or CT colonography) allows doctors to look at the large bowel to detect polyps and signs of cancer.

The large bowel, also called the colon, is the lower part of your intestines. It absorbs water and nutrients from digested food that passes through it.

The computerised tomography (CT) scanner uses X-rays to produce two-dimensional and three-dimensional images of the whole of the colon and rectum. The images are either stored on film or kept in a digital format and shown on a computer screen.


A polyp is extra tissue that grows on the inside of the bowel wall. It is usually harmless but can sometimes turn into cancer. To be safe, polyps are removed and tested for cancer.

About the procedure

Virtual colonoscopy is routinely done as an out-patient procedure. The scan will be performed by a radiologist, a doctor trained in radiology. The radiologist is usually assisted by a skilled technician, called a radiographer.

You may need to follow a special diet for a few days before the procedure and take a laxative to help clean the inside of your bowel out. Alternatively, you may need to swallow an iodine-based fluid, called a contrast agent, with meals around two days before the test. This fluid will help show the bowel more clearly on the X-ray.

The procedure usually takes 10 to 20 minutes. You may be given an injection of a muscle relaxant to help relax the muscles of the bowel wall. You may also be given an injection of contrast at the same time.

The scanner is a large machine with a hole in the centre (like a ring). Only the part of your body inside the ring can be scanned. You will be asked to lie on a table that can slide in or out of the ring.

A thin tube will be placed into your rectum. Carbon dioxide or air will be passed into your colon to make the bowel wall easier to see. When this happens, you may briefly feel pains similar to trapped wind and the urge to go to the toilet, but as the colon is empty, this will not be possible.

The table will be positioned so that the middle part of your body is lying in the centre of the scanner. The X-ray unit will rotate around you to help produce images from all directions. The scanner is operated from behind a window. Your radiologist will be able to see, hear, and speak to you throughout the procedure.

You will usually have scans taken in two positions - one with you lying on your back and a second scan with you lying on your stomach. It can take several minutes for each image to form and it’s important to lie very still during the process. At certain points during the scan you may be asked to hold your breath for a couple of seconds.

Virtual colonoscopy is a commonly performed and generally safe procedure. However, all medical procedures carry risks as well as benefits.

You will be exposed to some X-ray radiation. The level of exposure is about the same as you would receive naturally from the environment over 20 months. Pregnant women are advised not to have CT scans as there’s a risk the radiation may cause some damage to the unborn child.

Complications from virtual colonoscopy are uncommon. In rare cases, it’s possible to have an allergic reaction to the contrast injection. Medicines are available to treat any allergic reaction.

There is a small chance the colon may be damaged or perforated during the procedure. This can lead to bleeding and infection, which may require treatment with medicines or surgery.

Most people do not mind having part of their body in a CT scanner. But if you feel at all worried, please tell your radiologist.

Your doctor will explain the benefits and risks of having a virtual colonoscopy and discuss alternatives to the procedure. Depending on your symptoms, alternatives may include:

  • colonoscopy
  • sigmoidoscopy
  • barium enema

Please see the relevant Spire Healthcare treatment summary sheets for more information.

To find out more about having diagnostic tests with Spire Healthcare, please call you nearest Spire Healthcare hospital. Normally, you will need to obtain a GP or consultant referral before we can carry out any tests.

Find a treatment, test or scan available at:


Find a consultant

Use one or more of the options below to search for a consultant and link through to view their Spire profile.


Let us help you

fill out this form and we will get back to you:

Please select a hospital

We can call you

Please enter your details below and we will call you back.

What is the aim of your enquiry?

Please select a hospital

If we are unable to reach you by phone, please include your email address so that we can get in touch...

© Spire Healthcare Group plc (2016)