Siemens Diffusion Images
The Siemens Trio may writes out several images from a single diffuction run. These are (your suffixes may vary):
<prefix>_DTI_64 - the diffusion image itself, a 4D dataset with the 4th dimension being diffusion directions
<prefix>_DTI_64_ADC - calculated - the apparent diffusion coefficient - proportional to the speed of diffusion along the main diffusion axis at each voxel.
<prefix>_DTI_64_TRACEW -
<prefix>_DTI_64_FA - the fractional anisotropy map, calculated from the diffusion image, where values in the image represent deviations, per voxel, of the diffusion in that voxel from isotropy (equal diffusion in all directions).
See http://www.medical.siemens.com/siemens/sv_SE/gg_mr_FBAs/files/brochures/DTI_HT_FINAL_HI.pdf for more detail.