3D Shepp-Logan Phantom

3D extension of Matlab's phantom()

A 3D extension of MATLAB's phantom function - generates a phantom consisting of an arbitrary number of ellipsoids in 3D.
Matthias Schabel wrote this originally (thanks Matthias!); I made a small modification so that the size of the resultant 3D image can have anisotropic dimensions:
ph = phantom([256 128 32]);
... while still supporting custom ellipses.