1. A method of imaging a colon to obtain a desired cross-sectional image of at least one substantially thin segment of the colon, which image is generally perpendicular to the longitudinal axis of the colon lumen, comprising the steps of: (a) inflating the colon with gas; (b) scanning the abdominal region by using scanner means to obtain initial sets of data representing a plurality of first cross-sectional images of the entire colon taken along the longitudinal axis of the abdomen; (c) storing said initial sets of data in a memory; (d) processing said initial sets of data to reconstruct a three-dimensional image of the colon; (e) storing data representing said three-dimensional image in said memory; (f) displaying said three-dimensional image on a display; (g) using input means to select at least one substantially thin segment of said displayed three-dimensional image; (h) processing said initial sets of data and said three-dimensional image data to calculate a reconstructed cross-sectional image for said at least one segment that is disposed in perpendicular relation to the longitudinal axis of the colon lumen; and (i) storing data representing said reconstructed cross-sectional image in memory.