CT Colonography (Virtual colonoscopy)
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 short period of time. The information from the scan is then rapidly converted by powerful computers into 3 dimensional models of the bowel that can be looked through to find pathology.
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. The prep is similar to a standard colonoscopy.
The Macmurray centre has 2 Gastroenterologists who have trained to read these studies and in association with the Auckland Radiology Group we can offer these investigations with same day colonoscopy if intervention is required.
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.
This scan would be arranged by your Gastroenterologist from the Macmurray centre and would occur at 101 Remuera Road, very near our facility.
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.
The Radiologist and Gastroenterologist will study your images and discuss them with you immediately.
If a colonoscopy is required to remove a polyp or biopsy something that is found then this will be done straight away saving you the need to repeat the bowel cleansing on another occasion.
If a colonoscopy is not required you will be allowed to eat and drink and be discharged.
ROLE OF CT
For the diagnosis/exclusion of colorectal neoplasia in symptomatic patients, it is as accurate as barium enema. Patients with higher probability of neoplasia generally undergo colonoscopy, while those with a low probability could be assessed with CT colonography. Patients with bleeding generally are better undergoing a colonsocopy as a first test.
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, however there are concerns about the radiation risks.
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.
