Algodoo

CT stands for Computed Tomography, sometimes called a CAT scan (Computed Axial Tomography). This is a special type of X-ray machine that rotates around the subject (either human or animal) and it creates a number of X-ray image "slices" of the subject. The CT machine is capable of assembling the image slices into a 3D X-ray image.

This scene shows only 14 individual X-ray image slices of a human brain inside a skull. It is not a complete image of the brain because I only used a limited number of slices in order to demonstrate what a CT X-ray image looks like. You can see the individual slices, and also the assembled slices in a rough 3D rotating image.

See this article for more information on Computed Tomography:
http://en.wikipedia.org/wiki/Cat_scan