CT colonography (CTC) is an examination of the large bowel or colon. This is the last 1.5 metres of bowel, which extends from the region of the appendix to the rectum.
Advances in computerised tomography (CT or CT scanning) have enabled the lining of the bowel to be shown with exquisite detail. The data obtained during the scan is manipulated to produce 3D images. The radiologist can virtually “fly through” the colon, observing it in much the same way as an endoscopist does at colonoscopy (“virtual colonoscopy”).
CTC has several advantages over colonoscopy. It is less expensive, much less time consuming and doesn’t require sedation. Patients find CTC to be much more acceptable than colonoscopy. CTC has a high accuracy for detecting polyps and cancers in the large bowel, and is just as accurate as colonoscopy for detecting these. CTC provides the added advantage of displaying the organs and tissues outside the bowel, such as the liver and the kidneys.
What happens during CTC?
A small tube is inserted into the rectum and carbon dioxide is gradually pumped through the tube until you begin to feel a little uncomfortable. Most people find this to be less distressing than they had expected. An intravenous injection of buscopan is often given. This is a bowel relaxant, which prevents spasm and allows the bowel to distend adequately. Buscopan is contraindicated in people with heart arrythmiar and in men with prostrate problems.
A scan of the abdomen is made during a single breath-hold of 10-15 seconds. You will then turn over onto your stomach and another scan obtained. The entire examination should be completed within half an hour.
Preparation
In order to obtain a satisfactory CTC the bowel needs to be empty. Otherwise the scan will show the bowel contents and important abnormalities may be hidden. To clear the bowel for the examination, you will receive dietary instructions and a purgative mixture to encourage clearing of the bowel. It is very important to follow the dietary instructions closely and take the preparation at the times indicated. You may have to get up to the toilet during the night prior to the examination.
If you are constipated or have diarrhoea, please let our booking staff know, as you may need a modified preparation.
Afterwards
The carbon dioxide is absorbed rapidly into the blood stream and excreted through your lungs. You should feel little or no discomfort after the examination. You are able to drive.
