Brain damage has no bearing if you can still do the job. I don't see how a DTI changes you capability. A NeuroPsych Assessment is the usual diagnostic for mental capabilities.

If you had a concussion, you suffered brain damage. That is the nature of a concussion.

A full battery NPA can determine whether you have just depression caused MCI or whether it is organic or a combination of the two. It will also give you a good idea at specifically defining your strengths and weaknesses.

If you can find someone who really knows qEEG and uses one of the many good TBI discrimination databases, it can show an organic injury. Google qEEG, TBI and database and you will find lots of interesting information. qEEG has a 97% reliability at diagnosing an mTBI. You just need to find someone who is knowledgeable and uses a good comparative database.