CT colonography has added a new dimension to imaging of the colon. The resolution of MDCT allows for highly accurate reconstructions of the scanned volume. Special software algorithms produce a virtual reconstruction of the colon and allow the radiologist to navigate through it to identify any pathology.
CT colonography is an important screening tool for patients who might be at risk of developing cancer of the colon. This test can detect polyps and diverticular disease very accurately and is an alternative to the more invasive conventional colonoscopy. CT colonography is better tolerated by frail patients and is safer than normal colonoscopy.
The procedure involves the insertion of a short pipe into the rectum. An air puffer or automated insufflation machine is connected to this pipe and air or carbon dioxide is pumped into the rectum slowly. The gas distends the colon to improve visualisation. This is mildly uncomfortable and often the radiologist will give an injection of an anti-spasmodic agent to relax the bowel.
After the instillation of gas the abdomen is scanned in the supine (lying on back) and prone (lying on stomach) positions. The radiographers process the images and produce a virtual “fly-through” of the colon. This allows the radiologist to look at the colon in the same way a physician would look at it with a colonoscope.
Special preparation for a CT Colon:
Preparation is the key to a good examination.
Before the examination can be performed the colon must be cleared of faecal residue because this could obscure abnormalities in the colon as well as create the false impression of an abnormality. You will be requested to follow a specific diet the day before and to take special purgatives to clear the colon. This is outlined on an information sheet handed out at the time the examination is booked.
If you are a diabetic who needs to take medication with food, you are advised to bring something to eat with you. You can then take your medication immediately after the examination.