**Volume rendering**

The examined abnormality is not always well-connected to a certain surface. Volume rendering is used in these situations.

Suppose that each voxel emits and absorbs light as well. The light emitted from the ith voxel depends on the incident light and the ith voxel.

I_{i+1}=f(I_{i},V_{i}). It is usual that I_{0}=0 and I_{i+1}=C*I_{i}+V_{i}, where C is the absorption constant. If C=1 then this presentation is a projection without absorption.

Another special issue is the maximal intensity representation:I_{i+1}=max(I_{i},V_{i}).

Figure 47. Illustration of the bloodstream of the brain in a three dimensional maximal intensity image.

It cannot be decided if the plotted value is the bloodstream at the left or the right side of the brain.

This method can be applicable for seeking e.g. a tumor. A SPECT examination is done by a radiopharmacon concentrating in the tumor. Then instead of studying the images of a section, the visualization of the maximal intensity is more practical. These pictures do not show a three dimensional effect on their own. It can be achieved by e.g. the rotation of the formation.