Royal Free Consultant Gastroenterologist Dr Owen Epstein is conducting a prospective blinded-study, due to end in late Spring 2005, which is evaluating how the Viatronix V3D colonoscopy system compares with conventional optical colonoscopy.

Unlike some already-published screening studies, this one involves symptomatic patients, usually from the aged population. "Typical patients," says Dr Epstein, "rather than a group of fit and active subjects, to make the trial much more relevant to our usual workload."

Dr James Bell (pictured), the Consultant Radiologist performing the image interpretation, noted, "As the trial is not completed I am only able to comment on overall trends but the initial results are very encouraging.

The full results and comparison data will be collated at the end of the trial." Dr Bell reports that there is very good correlation between the two techniques with virtual colonoscopy being as good as optical in most cases.

For polyps greater than five millimetres, polyps behind haustral folds and for lower rectal polyps, VC is proving to be at least as good as optical colonoscopy. However, for polyps of less than five millimetres, optical colonoscopy is undoubtedly superior. Interestingly, these small polyps often missed by virtual colonoscopy, are not as significant as many are simply benign hyperplastic polyps and the chance of such small lesions containing a cancer is tiny.

There is also a higher completion rate with VC than conventional colonoscopy and a much-reduced chance of a perforation or cardiac complication.

"Radiologically, there are other advantages to CT colonoscopy. Because it scans the entire abdomen, we are able to see problems outside the bowel and it has the potential to be become much faster, especially if Computer Aided Detection meets its promise.

Also worth mentioning as a preliminary finding is that we have shown we can predict difficult colonoscopies from measurements of the length of sigmoid colon by V3D, " adds Dr Bell.

On the subject of ease of use, he comments, "The Viatronix system is very easy to use, with almost no time spent creating a 3-D model."

One area where VC is inferior to optical colonoscopy is that it involves exposing the patient to radiation. To be acceptable, especially in a screening environment, this dose must be as small as possible. As polyps are surrounded by air and so more readily distinguished from adjoining tissue, Dr Bell comments that it has been shown that it is possible to use a smaller dose for imaging. It is planned that at the completion of the trial, results will be quickly made available.

A meeting centred at the Royal Free Hospital on the topic of Endoluminal Imaging is planned for late Spring/early Summer where the data will be presented.