A computer system that segments a colon for a computed tomography colonography (CTC) is described. During operation, the computer system accesses imaging data having a spatial resolution. Then, the computer system identifies the colon lumen based on probabilities for different tissue classes in the imaging data. Moreover, the computer system segments the colon into subsegments based on an articulated object model that fits a tortuosity of the colon along a centerline of the colon, where the articulated object model includes values of an orthonormal basis set, curvature and torsion along the centerline, and where boundaries between subsegments are based on the curvature and die torsion. For example, a given boundary between a pair of subsegments may corresponds to or may be related to a minimum value of the curvature and a maximum value of the torsion over a length of the colon.