The purpose of this study is to evaluate the performance of a non-cathartic, computer-assisted form of CT Colonography (Virtual Colonoscopy) for detection of pre-cancerous colon polyps in a group of asymptomatic screening patients.

Examinations to completely assess the colonic anatomy for the purposes of polyp detection and cancer prevention all require an unpleasant, pre-exam cathartic bowel preparation. The discomfort and embarrassment associated with this bowel prep has been identified as a barrier to adherence of at-risk subjects with recommended colon screening guidelines. CT Colonography (CTC) is an imaging based test that evaluates the entire colon anatomy and requires cathartic bowel prep; its performance is considered comparable to optical colonoscopy (OC) for adenomatous polyp detection. In addition, CTC generates a large amount of data to be read by a human, and this data interpretation task can be aided by computer-assisted-detection (CAD) software to identify potential polyp lesions for the human reviewer. This trial studies the performance of a form of CTC that uses fecal tagging and electronic image cleansing to obviate the need for cathartic prep. In addition, readings prospectively employ CAD to potentially buffer human interpretation performance. The investigators are prospectively testing this augmented (non-cathartic, CAD-assisted) form of CTC in asymptomatic (screening) cohort. The trial is a prospective test comparison, using segmentally unblinded optical colonoscopy in combination with pathology specimens as a reference standard for presence of target lesions, adenomatous polyps 6 mm or greater in size.

Inclusion Criteria:

• age 50-80, eligible for colon screening

Exclusion Criteria:

• prior anatomic colon screening exam (optical colonoscopy, sigmoidoscopy, barium enema, CT Colonography) within last 5 years
• personal history of inflammatory bowel disease, polyposis syndrome, colo-rectal cancer, colon surgery
• documented passage of blood per rectum within last 12 months