Participants were placed on a CT table and a small flexible rectal catheter was positioned. N-butyl-scopolamine was administered intravenously if this was common practice in the participating center. Immediately before scanning, pneumocolon was obtained through insufflation of room air or carbon dioxide, either manually by means of a balloon pump or with an automatic device, until maximum tolerance was reached. CT colonography was performed with the participant in supine and prone positions with the following scanning protocol: 120 kilovolt peak (kVp), 50 or fewer effective mA per second, and a section thickness not greater than 1.25 mm.

Colonoscopy was performed at least 3 hours after CT colonography. The endoscope was advanced to the cecum and the entire length of the bowel was examined during endoscope withdrawal. The endoscopist was initially blinded to the result of CT colonography; at the end of each bowel segment evaluation, CT colonography results for that segment were disclosed (segmental unblinding). If a lesion measuring 6 mm or larger was detected at CT colonography but not at colonoscopy, the segment was reexamined to resolve the discrepancy

Each CT colonography study was read in two phases. In the first phase the radiologist interpreted the examination without activating the CAD algorithm. This phase of reporting was defined as unassisted reading. Then the radiologist activated the CAD algorithm which pinpointed a series of colorectal lesion-like structures (i.e. lesion candidates) on both the prone and supine acquisition. All lesion candidates were examined. The second phase of reporting was defined as CAD-assisted reading.