1. A method of identifying a polyp in a digital image of a colon, wherein said image comprises a plurality of intensities corresponding to a domain of voxels in a 3-dimensional space, said method comprising the steps of: providing the image with a set of 3 mutually orthogonal axes; centering, for each voxel in the image, a cutting plane about a central voxel at a first orientation with respect to the axes of the image; determining an intersection of the cutting plane with the colon, and examining a trace of the image within said intersection; and selecting, where the trace is small and round, those voxels in the intersection for further analysis.