One of the central problems of medical imaging is the 3D visualization of body parts. The 3D volume can be viewed in slices, but the extraction of a part requires a segmentation process. Inasmuch as body parts are distinguishable by their various densities, the best method to extract an organ is to extract iso-density surfaces by a simple threshold. Unfortunately the density of organs, arteries, etc. varies spatially due to morphology and no unique threshold allows one to extract the organs boundaries. The snake or active contours methods have attempted to capture these boundaries as smooth and overall contrasted surfaces. The snake method suffers, however, from severe drawbacks. The contour has to be initialized near the boundary. In addition many body parts have a too complex topology. In this paper we focus on another idea, which is to preprocess the image before thresholding. The preprocessing aims at the homogeneity of the different parts while preserving small features. Starting...