Conformal Mapping of the Inner Colon Surface to a Cylinder for the Application of Prone to Supine Registration

CT-Colonography is widely utilised in the diagnosis of colorectal cancer. However, the technique is difficult and time-consuming because residual stool may simulate colorectal cancer or potentially precancerous polyps. Consequently, scans are routinely performed with the patient in both prone and supine positions to help differentiate mobile faecal matter from fixed abnormalities of the colonic wall. Currently, the prone and supine datasets have to be manually aligned which can be very difficult due to the significant colonic deformation which takes place during patient movement. Establishing accurate spatial correspondence between prone and supine inner colon surfaces reconstructed from CT images can therefore potentially improve the accuracy and reduce the time taken for interpretation. This paper presents a method for mapping the inner colonic surface to a cylinder using the Ricci flow which provides a 2D indexing system over the full length of the colon. This procedure converts the registration task from a 3D to a 2D problem and could help cope with the large deformations occurring between prone and supine positions. c © 2010. The copyright of this document resides with its authors. It may be distributed unchanged freely in print or electronic forms. 2 AUTHOR et al.: CONFORMAL MAPPING OF THE INNER COLON SURFACE