CT Colonography Computer-Aided Polyp Detection using Topographical Height Map

CT colonography (CTC) is an emerging noninvasive technique for screening and diagnosing colon cancers. Computer aided detection (CAD) techniques can increase sensitivity and reduce false positives. We propose to employ topographical height maps in our CAD pipeline. For every detection, a height map is computed using a ray-casting algorithm. Since colonic polyps are protrusions outward from the colon wall and are round in contour, their height maps present concentric patterns. The projection direction is optimized through a multi-scale spherical search. We derive several topographic features from the map, and also compute texture features from the Haar wavelet coefficients. We send the selected features to a committee of support vector machines for classification. We have tested our method on 1186 patients with 226 polyps. Results showed that the height map features can reduce false positives by about 50%.