New CT colonography technique gets the nod from patients


Exiting a CT examination room in early May, Norman Alexander surprised even himself. Minutes after receiving his first CT colonography at St. Michael’s Hospital, Alexander was finalizing lunch plans before rushing off to an evening business meeting.With only a minor stomach ache, the Toronto businessman’s experience was the polar opposite from a year earlier when he underwent a colonoscopy. That procedure left Alexander vomiting and feeling the effects of throat discomfort for weeks.

“The two procedures are like night and day,” he explained immediately following the CT colonography. “If my doctor says I need it again, I would do it without hesitation.”

Known as “virtual colonoscopy” or CT colonography, the technique was first adopted by St. Michael’s Hospital in 2004 – one of the earliest in the city to begin conducting the new procedure, staff radiologist Dr. Arthur Zalev said. Three years later Dr. Zalev and colleague Dr. Wayne Deitel have successfully conducted more than 110 CT colonography examinations.

CT colonography, used by radiologists to detect colon and rectal polyps and cancer, has been gaining ground in medical circles in recent years. A 2003 study in the New England Journal of Medicine found CT colonography is proving to be as effective as traditional colonoscopy in detecting polyps or abnormal growths that may lead to cancer.

“CT colonography goes where colonoscopy has been unable to go before,” Zalev said. “The technique is less invasive and faster than colonoscopy, requires no sedation, and is a good alternative for many patients unwilling to undergo colonoscopy or patients who have had an incomplete colonoscopy because of obstruction or technical difficulties.”

The procedure involves filling the colon with air or carbon dioxide after inserting a flexible rubber tube into the rectum. A CT scan is then performed with the patient lying face up and face down. The image data, which contains hundreds of cross-sectional images of the abdomen, is then combined and digitally manipulated by computer software to produce 3-D images of the bowel. The results appear similar to what a doctor views in a conventional colonoscopy procedure.

“CT colonography may also allow for discovery of other serious conditions outside the large bowel, which occur in about one in eight patients who will then need further study of the abdomen or lower chest,” Zalev added. “This technique may detect serious conditions unrelated to the large bowel such as aortic aneurysms and kidney tumors.”

Drawbacks of the system include exposure to low levels of radiation, less precision in differentiation of stool from polyps, cost, and the need for colonoscopy after a positive CT colonography.

However, for Alexander, the benefits far outweigh the costs.

“If it achieves the same thing as a colonoscopy, this is far superior from a comfort point of view and efficient,” he said.

Statistics on the effectiveness of CT colonography point to 90 per cent sensitivity for detecting polyps greater than one centimeter on a per patient basis. Polyps of this size often go on to form malignant tumors.

A leading cause of cancer-related deaths in Canada, colorectal cancer can be successfully treated if caught early through screening procedures such as colonoscopy and CT colonography.

“While colonoscopy remains the gold standard for screening the entire colon to detect early cancer, the improvement in the clinical effectiveness of CT colonography suggests this new technique may be a first line alternative to conventional colonoscopy,” Zalev said.