Computer-aided detection of polyps in a colon phantom: Effect of scan orientation, polyp size, collimation, and dose

Purpose: To determine the importance of polyp size, orientation to the scan plane, collimation, scanner type (single or multislice helical), and radiation dose on computed tomography (CT) colonography computer-aided detection. Materials and Methods: Eight tissue-equivalent simulated polyps were placed into the interior of an air-filled acrylic tube placed within a water-filled box. Their sizes, expressed by diameter and height in millimeters, were 10 × 10, 10 × 7, 10 × 5, 10 × 3, 7 × 7, 7 × 5, 7 × 3, and 5 × 5. Detection of the polyps was performed by applying our prototype automated polyp detector software to 48 CT colonography data sets of the phantom acquired with different CT scanner settings. Results: We detected at least six of the eight polyps in 47 of 48 experiments. The two most frequently undetected polyps (7 × 7 and 5 × 5) had extreme eccentricity (their height was twice the radius of the base) and were most commonly missed for 90° tube orientation, 5-mm collimation, and high table speed. False-positive detections occurred in only 5 of 48 experiments. Conclusion: Clinically significant 10-mm polyps can be detected with 100% sensitivity in all orientations, doses, collimations, and modes that we examined.