Combination of volume and surface rendering

Figure 48.

 
Sometimes in the point of view of the medical finding, it is not the surface’s shape which is the most informative, but the operation of a part of the organ that is close to the surface. For instance the blood supply of the brain’s gray matter is an example for it. The brain’s gray matter is relatively thin but with radioisotopic method the amount of bloodstream can be determined inside the gray matter, not on the surface. In order to visualize it in three-dimension, firstly the surface of the matter is defined, then at the visible superficial points the normal vectors are calculated. Finally, on the extrapolated line of the normal vector the voxel corresponding to the maximal bloodstream up to a given depth is found. That voxel describes well the bloodstream at that part of gray matter. The given point of the surface is colored according to the color coded value of that voxel.