CT Colonography

CT colonography (CTC) is a relatively new method of investigating the large bowel. It is made possible by the availability of multislice CT scanners that are able to scan the entire abdomen and pelvis with fine slices in a single breathhold. Equally important is the increased speed of computers to process this large data set and display it in a useful and interactive format.

PREPARATION

The extent and type of bowel preparation depends on the patient's age and condition. Ideally, the entire colon should be cleared of solid material, and to achieve this, we have a special diet and laxative regime regime that starts the day before the examination.

For the elderly or others who cannot tolerate the usual preparation, we give them a special barium mixture that they drink regularly over 3 days. They do not have to take laxatives or restrict their diet. This preparation "stains" the bowel contents and allows us to differentiate tumours from faeces.

WHAT TO EXPECT

You will be asked to remove all of your clothing, and will be given a gown to wear. You will then be taken to the CT scanning room. Carbon dioxide gas will be introduced into your bowel so that the surfaces are clearly outlined. To achieve this the radiographer will gently introduce the gas through a small tube passed into your rectum (bottom). It is the same gas that is used to make soda water, and it is extremely safe to use.

Two scans will then be performed: one scan with you lying on your back, and the other lying on your tummy. Each scan takes only a few seconds.

AFTERWARDS

There will be some gas in your bowel and you may feel a little uncomfortable and bloated. However, your body will absorb the gas very quickly so the discomfort should disappear by the time you leave the department. There may be some fluid or residue still in your bowel so do not stray from the access to a toilet.

You may eat and drink normally immediately after the examination.

The radiologist will study your images and the report will be sent to your doctor.

3-D Surface Reconstruction

ROLE OF CT

For the diagnosis/exclusion of colorectal neoplasia in symptomatic patients, it is as accurate as barium enema. Patients with high probability of neoplasia generally undergo colonoscopy, while those with a low probability could be assessed with CT colonography.

CTC is especially useful in elderly/frail patients as it is better tolerated that a barium enema.

Incomplete colonoscopy: A CTC is usually performed on the same day as the colonoscopy and is very helpful to demonstrate the parts of the colon that colonoscopy fails to reach.

Screening for colorectal neoplasia: At present high-risk subjects undergo screening colonoscopy. For average risk subjects, there is no consensus on the best method of screening and CTC may become increasingly used in this role.

NB: CTC is not suitable for mucosal diseases such as inflammatory bowel disease or angiodysplasia.

ADVANTAGES OF CTC

No sedation required.
Rapid examination.
Better tolerated by patients than barium enema, as the patient does not have to turn over and over so much, there is less risk of soiling, and less bloating and spasm after the examination.
CTC displays all the abdominal organs, so it finds more abnormalities than just in the bowel.

CT Colonography is available at St. George's Radiology and Southern Cross Radiology. Please feel free to speak with any of the radiologists if you have any questions about this procedure or suitability for individual patients.