Virtual colonography

Cross-sectional imaging techniques are increasingly being considered as alt ernative imaging modalities for colorectal screening. While CT-colonography uses air to insufflate the colon, an enema containing small amounts of par amagnetic contrast represents the basis for MR-colonography. Both technique s provide large three-dimensional data sets of the abdomen, containing the entire colon. Using sophisticated post-processing, the colon can be assesse d in any desirable plane from various viewpoints. Thus even virtual endosco pic views can be rendered to assess the inside of the colon. This chapter b riefly describes the technical aspects underlying both CT- and MR-colonogra phy. Advantages and disadvantages of the two techniques are critically disc ussed, comparing them with one another as well as with conventional colonos copy and barium enema.