Fold removal in CT Colonography: A Physics-Based Method

Computed Tomographic Colonography (CTC) produces 2-d and 3-d images of the colon using computed tomography (CT). The main goal of CTC is to detect small lumps on the colon surface called polyps, which are known to be precursors to colon cancer. Radiologists are therefore interested in exploring the inner surface of the colon to detect polyps. Polyps may be detected by visual inspection of colon CT images and also by using computer-aided detection. The colon surface is abundant with folds that occlude polyps during visual inspection and also contribute to false positives in computer-aided polyp detection. Removal of folds should therefore improve visualization and could also improve polyp detection sensitivity. In this paper, we present a physics-based method to unfold the colon surface. The output of our algorithm is a surface in 3-d, with the folds flattened out, leaving only polyps behind. Preliminary tests of our method in mathematical phantoms and actual patient data show reductions in fold height and curvature ranging from 54.4% to 70.3%, and 36.3% to 86.1% respectively. Polyp size and curvature were reduced by only 0 to 16%, and 0 to 20%, respectively. Our method, thus, demonstrates potential for improving both visual and computer-aided detection of colonic polyps from CTC examinations.