smutsik,

From what I have read about DTI is it just shows an increase in fluid flow compared to the normal. The science has not yet defined why that increased flow exists other than to observe that is coincides with an injury and/or anxiety/depression. Whether it is axon related, myelin related, inflammation, edema, or ischemia, nobody appear to know yet. Damaged myelin is as problematic as damaged axons. Axons have greater healing potential than myelin. Folic acid, B-12 and such help with myelin healing. The other issues disrupt normal function.

If you want to fry your brain trying to understand DTI, here is a good article.
Diffusion Tensor Imaging of the Brain