Virtual colon flattening based on colonic outer surface

Virtual colon flattening (VF) is a non-invasive procedure to inspect the colonic inner surface for detecting colorectal polyps. Unfortunately, the performance of VF is impeded by deformation distortions of colonic inner surface. Conventionally, the colonic inner surface itself is used to correct deformation distortions. In this paper, we propose a colonic outer surface based VF method to correct distortions instead of colonic inner surface. The proposed method was validated with 60 cases and 200 annotated polyps. Visual inspections were carried out by three operators independently and were compared with three existing VF methods which are based on colonic inner surface. The correct detection rate of the proposed method and the three existing methods were 88.0%, 76.5%, 80.0% and 81.5% respectively. False positives per case were 0.16, 0.32, 0.21, and 0.26 respectively. The proposed method has higher correct detection rate and less false positives than the other three VF methods, demonstrating the usefulness of colonic outer surface as a correction tool for VF results.