Currently utilized screening methods include: digital rectal examination with fecal occult blood evaluation, double contrast barium enema, flexible sigmoidoscopy and optical colonoscopy. While optical colonoscopy is the most accurate method, it is not fully utilized for mass screening. Optical colonoscopy, usually performed by a gastroenterologist using patient anesthesia, enables viewing and removing polyps through a colonoscope. The colonoscope is inserted into the rectum and moved throughout the colon. This invasive procedure requires extensive patient preparation, introduces potential risks of infection and/or perforation. Furthermore, it can be ineffective in examining areas of the colon blocked by masses, in areas of severe narrowing or behind colonic folds.

Virtual colonoscopy is a new procedure utilizing abdominal CT images and a computer visualization system to identify polyps by navigating within a reconstructed 3-D model of the colon (2,3). The patient undergoes a less vigorous bowel preparation. It consists of a modified diet, oral agents to tag residual stool and fluid for computer based, electronic removal and little if any physical bowel cleansing. After inflating the colon with carbon dioxide (better tolerated than room air) introduced through a small rectal tube, spiral CT images are then taken in seconds (by breath holding) yielding one millimeter resolution in the axial and sub millimeter resolution in the in plane directions, with excellent contrast between the colon wall and the lumen. Advanced image segmentation creates clean 3-D colon reconstruction and computer graphics enables navigation through it.

Since its initial description, virtual colonoscopy has received a great deal of attention as a promising method for colon cancer detection. Its many advantages, compared to existing modalities, have been the focus of study for several US and international research groups. Recent technical advances have occurred in patient preparation, data acquisition and interpretation, and image display that now make widespread implementation of virtual colonoscopy a practical reality. An additional large-scale, multi-institutional scientific evaluation is in progress to further validate earlier studies on the effectiveness of virtual colonoscopy. The November 17 FDA 510(k) clearance for v3D-Colon™ is likely to accelerate scientific research, and begin the process of adoption of virtual colonoscopy as a screening tool for the general public.

State University of NY at Stony Brook
Medical Director, Viatronix™