Purpose: To determine the performance characteristics of multidetector CT colonography (CTC) in an asymptomatic screening population, using optical colonoscopy (OC) as the reference standard.

Methods and Materials: 839 asymptomatic patients for screening (mean age, 57.5 years) underwent CTC followed by same-day optical OC. Bowel preparation consisted of phospho-soda and dilute oral CT contrast in 2 divided doses. Multidetector CT scans were performed during a single breath hold in supine and prone positions, after rectal insufflation of room air. Multidetector CT parameters included 4 x 2.5 mm or 8 x 1.25 mm detector configuration, 15 mm/sec table speed, and 1 mm reconstruction interval. Immediate prospective interpretation of CTC studies was performed prior to OC, with segmental unblinding of CTC results at OC. CT readers employed a primary 3D approach for polyp detection, using 2D images for confirmation and problem solving.

Results: CTC sensitivity for adenomatous polyps on a by-patient basis was 93.3% (28 of 30), 94.2% (49 of 52), and 89.1% (98 of 110) for polyp size thresholds of 10, 8, and 6 mm, respectively. At the same size thresholds, OC sensitivity by patient for adenomatous polyps prior to unblinding was 86.7% (26 of 30), 90.4% (47 of 52), and 89.1% (98 of 110), respectively. CTC specificity by patient for all polyps was 97.7% (767 of 785), 94.8% (706 of 745), and 84.4% (550 of 652) at 10, 8, and 6 mm thresholds, respectively; CTC specificity by patient for adenomatous polyps was 95.6% (773 of 809), 90.9% (715 of 787), and 78.2% (570 of 729), respectively. CTC sensitivity by polyp for adenomas was 90.9% (30 of 33), 92.1% (58 of 63), and 85.4% (117 of 137) at 10, 8, and 6 mm thresholds, respectively. 0.3% (1 of 359) of all adenomatous polyps harbored malignancy. Mean patient time in the CT suite was 14.1 minutes, compared with 33.0 minutes in the colonoscopy suite (not including recovery time). Mean CTC interpretation time by site (including extracolonic findings) was 17.0, 18.8, and 25.6 minutes.

Conclusion: CTC with primary 3D interpretation is an accurate screening method for detection of colorectal neoplasia in asymptomatic adults, despite the low prevalence of disease. This minimally invasive total colonic examination compares favorably with the reference standard (OC) for detection of clinically significant lesions.