Study participants underwent colonic preparation with oral intake of 90 mL of phospho-soda and 10 mg of bisacodyl. To opacify residual colonic fluid and stool for VC examination, patients also consumed dilute oral contrast as previously described (7). Our CT protocol and VC technique have also been detailed previously (6). To briefly summarize, we obtained supine and prone CT acquisitions on multidetector scanners after patient-controlled rectal insufflation of room air. One of 6 trained radiologists interpreted VC studies by using a commercially available CT colonography system (Viatronix V3D-Colon, version 1.2, Viatronix, Inc., Stony Brook, New York). We used the 3-dimensional endoluminal fly-through view primarily for detecting polyps and 2-dimensional images for confirmation and problem solving. We measured polyps on the 3-dimensional view and recorded them by segment (cecum, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon, or rectum). We defined the proximal colon as including the cecum to the splenic flexure. We prospectively rated diagnostic confidence for each detected lesion on a 3-point scale (most certain, intermediate, and least certain).