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What is CT Colonography?

CT Colonography (Virtual Colonoscopy) is a very accurate and safe test used to rule out bowel cancer and its precursor, the advanced colonic polyp. It is an alternative to colonoscopy and frequently preferred by patients for the following reasons:

  • Less invasive and avoids sedation
  • Less disruptive to daily activity (many people go to work after their appointment)
  • Fewer laxatives
  • Examines important organs which surround the bowel for example helping to rule out aortic aneurysm, lymphoma or abnormalities of the kidneys, pancreas, ovaries, liver and spleen.
  • Examines appendix (not seen well at colonoscopy)

By confidently excluding disease in the colon and surrounding organs, CT Colonography provides reassurance and enables patients and their doctor to focus on alleviating their symptoms.

Dr David Burling and Dr Andrew Plumb are leaders of the London Radiology’s CT Colonography team. David and Andrew are national and international leaders in this field with unparalleled experience dedicated to delivering the highest quality patient experience.



What is a CT scan?

A CT scan utilises X-rays to produce highly detailed images of the body allowing the Radiologist, a doctor trained in interpreting scans to accurately identify abnormalities within the organs of the body.

Scans frequently take a few seconds, although you will usually be in the scanner room for a few minutes whilst the radiography team helps to plan your scan.

CT scans are generally very well tolerated, without discomfort or claustrophobia. Most scans will require an intravenous cannula to allow contrast dye to be injected (to enhance the quality and accuracy of your scan).


Who can have CTC?

Q. Can anybody have this test?

A. As this test uses radiation, we usually avoid performing it on patients under the age of 40. However we treat every patient individually and there are often exceptions. This test is generally not suitable for those patients who have, or are suspected of having inflammatory bowel disease (Crohn's disease or ulcerative colitis) or who have an established colon polyposis syndrome.

Q. Can I have this test if I don't have any bowel symptoms?

A. You can have this test whether you have bowel symptoms or not (as a 'screening' test). However many insurance companies only cover the test if you have symptoms and so you may need to self pay in this scenario.

Before the Scan

Q. Is this test as accurate as colonoscopy?

A. A recent large study (SIGGAR study of over 5000 patients in the UK published in the Lancet 2013) has been performed, comparing this test to colonoscopy and barium enema. CTC was shown to be as accurate as colonoscopy for detection of cancer and large bowel polyps (the precursor of cancer) and superior to the existing radiological test, barium enema.

Q. Is this test similar to a barium enema?

A. No, this test is different, using a CT scanner, no liquid enema and requiring less patient movement. CTC is better tolerated than barium enema and more accurate.

Q. Is this test just for my bowel or will it show anything else?

A. CTC will provide information about organs outside the bowel within your abdomen and pelvis including detection of aortic aneurysm and review of liver, pancreas, spleen, pelvic organs and kidneys.

Q. I have already had a colonoscopy which was difficult; how is this test different?

A. During this test a small flexible tube (diameter of a pencil) is inserted into the rectum through which gas is passed. The gas will gradually fill the loops of bowel which is achieved more easily than trying to pass the scope around the bowel.

Q. Last time I had a test that involved laxatives I found it very difficult to manage, is there an alternative to standard 'full' laxatives?

A. Yes. The bowel can be prepared by using a liquid which mixes with the bowel contents so that they can be seen on the scan (and rapidly discriminated from polyps or cancer). This liquid may give you diarrhoea, but on average is easier to manage than taking standard bowel preparation (strong laxatives).

Q. I am diabetic, can I still take the bowel preparation?

A. Yes. 1. If your diabetes is controlled only by tablets or by diet and you are able to measure your own blood sugar then most people can continue with the diet as instructed. Taking laxatives can reduce your blood sugar so you may have to monitor your blood sugar level more frequently than usual. If you have difficulty managing to maintain a balanced sugar level, please see below. 2. If your diabetes in controlled by insulin or if you have difficulty in maintaining a balanced sugar level we can adjust your preparation accordingly – please phone us. Q. Why do I need to be on a restricted diet for one or two days before this test? A. Some foods make it more difficult to clean the bowel. The diet recommended for CTC is designed to help with the bowel preparation.

The Scan

Q. This test involves radiation; how much radiation will I receive and is it dangerous?

A. We use as little radiation as we are able to, whilst making sure that the scan is of adequate quality. The amount of radiation needed will depend upon various factors including the reason why the scan is being performed and if additional scans are required. For most patients, it is possible to use a low dose which would be equivalent to 1-2 years of average UK background radiation (to which we are all exposed).

Q. Why are scans often done first thing in the morning?

A. Our patients generally prefer to be scanned at the beginning of the day for several reasons • There is no need to spend the day without eating. • Less time off work is needed- many people go to work straight after their test. • If the scan indicates that an additional test is required we may be able to organise it for the same day.

Q. Will I have sedation for this test and will I be able to drive home afterwards?

A. Sedation or pain relief is not needed for this test. Most people find that it can be a little uncomfortable, but as soon as the test is finished the discomfort will ease. Because there is no sedation, this test will not affect your ability to drive.

Q. Are there any risks involved in having this test?

A. As with any test to examine the bowel, there is a small risk of making a tear (perforation) in the lining of the bowel. The risk of that happening with this test is less than 1 in 3000, which is safer than barium enema and colonoscopy. Even where perforation occurs, many patients have no symptoms at all and very few will require further intervention. If you are given any drugs during your test the radiographer performing the test will give an explanation of any potential risks or side effects they may have.

After the Scan

Q. What happens if an abnormality is found in my bowel?

A. Usually you will find out the result of your scan from the doctor who asked us to perform it, or the radiologist (a medically qualified expert in interpreting scans). You and your doctor will then decide what to do next if any treatment is needed. However, if further tests are required we may try to organise them for the same day, especially if this means you do not have to have another bowel preparation.

Q. If polyps are found in my bowel, do I have to have them removed?

A. Your doctor will discuss this with you. Generally, large polyps measuring 1 centimetre or more in diameter should be removed or biopsied at endoscopy, but smaller polyps may be left, and monitored by follow up scans. This decision is made on an individual basis and will not be the same for everyone. Your radiologist will discuss this fully with you and/or your doctor.

Types of CT scan

Body CT

Body CT examines the chest, abdomen and pelvis and will frequently be used to investigate new symptoms or for surveillance of disease following treatment.

CT enterography

CT enterography is a technique used to investigate the small bowel (3 to 4 metres long and located between stomach and large bowel). CT enterography involves patients drinking quite a large volume of water (1-2 litres) mixed with a liquid to help the water stay in the bowel.This technique also examines other organs in the abdomen and pelvis providing a comprehensive imaging review to help explain patients' symptoms or assess the severity and extent of known small bowel disorders.

Are there any risks associated with X radiation?

Whilst CT scanning uses X-rays, the radiation dose used for medical imaging tend to be very low and equivalent to 1 to 3 years of average background radiation found in the UK (from naturally occurring radiation in the rock and earth). Whilst there is theoretical harm from radiation by slightly increasing the risk of developing cancer (about 1 in 10,000 people), there is a lack of evidence showing harm to adults patients undergoing CT for diagnostic imaging. Indeed, some physicists advocate small radiation doses might confer benefit, for example airline pilots are exposed to increased radiation dose (cosmic radiation) and have lower rates of cancer compared to the general population. Overall, London Radiology has a judicious approach to using radiation by keeping dose as low as reasonably achievable. In practical terms this means avoiding use of X-radiation in children and young adults where possible and limiting dose for our adult clients to optimise the balance between benefit and risk.

Self Referral for CT Colonography