Hi Brian,
DICOM is pretty much the industry standard, and usually consists of a stack of scan images (float) with metadata.

For cross platform, take a look at ImageJ, it's free & powerful with tons of plugins.

On OsX the best program is OsiriX, which is outstanding for volumetric data processing in general.

If you Google " CT stack " or "DICOM data" you should find some examples pretty easily. YouTube also has some examples.

The example I used was from the Wikipedia "Computed Tomography" page :)

-FDP