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Virtual colonoscopy (CT colonography)

Published by Bupa's health information team, July 2009.

This factsheet is for people who are planning to have a virtual colonoscopy, or who would like information about it.

Virtual colonoscopy is also called computerised tomography colonography (CTC). Virtual colonoscopy is a procedure that allows doctors to examine the large bowel (colon) for polyps and signs of cancer.

Your care will be adapted to meet your individual needs and may differ from what is described here. So it's important that you follow your doctor's advice.

• About virtual colonoscopy
• What are the alternatives?
• Preparing for a virtual colonoscopy
• About the procedure
• What to expect afterwards
• What are the risks?
• Questions and answers
• Related topics
• Related Bupa products and services
• Further information
• Sources

About virtual colonoscopy

Virtual colonoscopy can be used to examine your large bowel if you have symptoms such as changes in your bowel habit, weight loss or blood in your faeces, which can be symptoms of bowel cancer. It can also be used to screen people who are at risk of developing bowel cancer. The scanner uses X-rays to produce three-dimensional images of your large bowel and rectum (back passage).

Virtual colonoscopy can show polyps and abnormalities on your bowel wall. Polyps are small growths on the inside of your bowel. They are usually harmless but they can sometimes develop into cancer.

What are the alternatives?

There are several other tests that can detect cancers and polyps.

• Conventional colonoscopy. This procedure allows your doctor to look inside your bowel using a narrow, flexible, tube-like camera called a colonoscope. Your doctor can inspect the wall of your bowel by looking directly at the bowel lining on a monitor.
• Sigmoidoscopy. This is like a colonoscopy, but it only looks at the lower part of your bowel.
• Barium enema. This test involves placing a fluid containing barium (a dye which shows up on X-rays) into your bowel via your rectum. X-ray images of your abdomen (tummy) can then show the inside of your large bowel more clearly.

Your choice of test depends on several factors. Virtual colonoscopy, for example, can be an easier and more comfortable procedure for some people to have than conventional colonoscopy. Your doctor will explain your options to you.

Preparing for a virtual colonoscopy

Your doctor will explain how to prepare for your scan. For your doctor to be able to see your bowel clearly, you may need to follow a special diet for a few days before the procedure and take a laxative to empty your bowel.

In addition, you may be asked to swallow an iodine-based fluid called a contrast agent (dye) around two days before the test. This fluid will help to show your bowel more accurately on the scan.

Virtual colonoscopy is routinely done in the X-ray department of the hospital. The scan is performed by a radiologist (a doctor who specialises in using imaging methods to diagnose medical conditions). The radiologist is usually assisted by a radiographer (a health professional trained to perform imaging procedures).

Before the procedure, you should tell your doctor about any medicines you're taking and if you have any allergies. Also, let your doctor know if you are, or you could be, pregnant. Virtual colonoscopy isn't recommended for pregnant women, unless there is an urgent medical reason.

Your doctor will ask you to sign a consent form. This confirms that you understand the risks, benefits and possible alternatives to the procedure and have given your permission for it to go ahead.

About the procedure

The scan usually takes between 10 and 20 minutes.

In a private cubicle, you will be asked to remove your clothes and put on a hospital gown.

You will be taken to the scanning room. 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 need to lie on a table attached to the scanner. This can slide in and out of the ring.

You may be given an injection of a muscle relaxant to help relax the muscles of your bowel wall. You may also be given an injection of contrast agent at the same time, depending on the reason for the test.

A thin tube is placed a few centimetres into your rectum. Carbon dioxide or air is gently passed into your colon to make the bowel wall easier to see. When this happens, you may briefly feel pains similar to trapped wind. You may also have the urge to go to the toilet, but because your colon is empty, this won't happen. You may pass wind, but there is no need to feel embarrassed, as the staff expect this may happen.

The table will move into the ring of the CT scanner 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 every direction.

The scanner is operated by the radiographer from behind a window. He or she will be able to see, hear and speak to you throughout the procedure.

You will have some scans taken with you lying on your back and others taken with you lying on your stomach. At certain points during the scan you may be asked to hold your breath for a few seconds. It can take several minutes for each image to form and it's important to lie very still during the scan.

What to expect afterwards

You will be able to go home when you feel ready.

If you have had muscle relaxants or an injection of contrast agent, you will need to wait for an hour before driving. You may want to arrange for someone to drive you home after the scan.

If you're breastfeeding, it's recommended that you wait 24 hours after having a contrast agent injection before you breastfeed. You may need to express and discard your milk for 24 hours after the scan. Ask your doctor or radiographer for specific advice.

Your results are usually sent in a report to the doctor who requested your scan. The report can take a few days to reach your doctor.

If you haven't been told the results of your scan within two weeks, contact the doctor who requested your scan for advice.

Virtual colonoscopy is used to diagnose a condition rather than to treat it. If the virtual colonoscopy finds that you have polyps, you will need to have either conventional colonoscopy or a sigmoidoscopy to remove them. Large polyps or cancer might need surgery to remove them.

What are the risks?

Virtual colonoscopy is commonly performed and generally safe. However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications of this procedure.

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.

If you're pregnant then you shouldn't have a CT scan as there is a risk that the radiation may cause some damage to your unborn child.

Side-effects

These are the unwanted but mostly temporary effects you may get after having the procedure. The main side-effects are described below.

• Laxatives used to prepare your bowel cause diarrhoea and may make you feel sick and bloated.
• Very rarely, you may sense a warm feeling or get a metallic taste in your mouth after having a contrast injection. This usually lasts only a minute or two.
• If you have had muscle relaxants, these can temporarily blur your vision or make you feel dizzy.

Complications

This is when problems occur during or after the procedure. Complications from virtual colonoscopy are uncommon.

In rare cases, it's possible to have an allergic reaction to the contrast agent injection. Let your doctor know if you're allergic to iodine. If you experience any itching or difficulty in breathing tell your radiologist immediately. Medicines are available to treat an allergic reaction.

There is a very small chance that your colon may be damaged or torn during the procedure. This can lead to bleeding and infection, which may need treatment with medicines or surgery.

The exact risks are specific to you and differ for every person, so we haven't included statistics here. Ask your doctor to explain how these risks apply to you.

Related topics

• Barium enema
• Bowel cancer
• Colonoscopy
• CT scan
• Flexible sigmoidoscopy

Further information

• Beating Bowel Cancern
  08450 719300
  www.beatingbowelcancer.org

Sources

• Computed tomographic colonography (virtual colonoscopy). National Institute for Health and Clinical Excellence (NICE). www.nice.org.uk, June 2005
• CT colonography (virtual colonoscopy). Radiology Info. www.radiologyinfo.org, accessed 15 February 2009
• CT Scan. Royal College of Radiologists. www.goingfora.com, accessed 15 February 2009
• Information for patients having a CT scan. Royal College of Radiologists. www.rcr.ac.uk, accessed 15 February 2009
• Administration of contrast medium to breastfeeding mothers. American College of Radiology. www.radiologyinfo.org, accessed 15 February 2009
• Joint Formulary Committee, British National Formulary. 56th ed. London: British Medical Association and Royal Pharmaceutical Society of Great Britain, 2008; 58: 568.
• Intravenous pyleogram. Radiology Info. www.radiologyinfo.org, accessed 15 February 2009

This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.

Publication date: July 2009