Fast Extraction of Planes Normal to the Centreline from Ct Colonography Datasets

CT Colonography (CTC) is an emerging imaging technique for colon screening. It is possible to extend this technique to automatically detect colonic anomalies. In order to improve the detection rate of the potential polyps, it is desirable to analyse plane sections orthogonal to the colon centreline rather than the axial CT slices. This paper describes a fast artefact free method for orthogonal plane extraction. The centreline in its initial form lacks the smoothness required to provide accurate local orientation of the colon. An approach based on down-sampling and B-spline interpolation generates a suitable smooth centreline. The cubic B-spline form gives low cost access to accurate local orientation and curvature of the colon. The local orientation is used as a normal vector for the orthogonal plane. The plane extraction from the anisotropic CT dataset is divided into two stages. First, a projection of the orthogonal plane on one of the dataset faces is created. A bilinear interpolation on the projected plane extracts the actual viewing window. This plane extraction is fast: extracting a plane using trilinear interpolation requires ~7*N linear interpolations, our method achieves the same image quality and requires only ~3*N linear interpolations. This technique can be use to analyse cross-sections of the colon without significant processing overhead.