Mark is right. Currently DTI MRI is considered a suitable imaging technology for showing impact (damage) to the brain resulting from all categories of TBI, including mild TBI. It's based on following water diffusion along axonal tracts in the brain. Since damage linked to mTBI traditionally is associated with anterior/posterior contusions and/or damage to axonal tracts, this technology is highly relevant. Mark actually introduced me to this technology a few months ago in one of my early posts. I'm currently trying to get one of these arranged.

Regarding DTI, there was a recent review and meta-analysis of neuroimaging published by Eierud et al. (2014) in which DTI was shown to be a useful tool for mTBI. In particular, differences in brain anisotropy for controls and individuals with acute and chronic PCS were consistently reported. Interestingly, the brains in acute and chronic PCS showed stark differences as well. In the review, the authors state that the application of DTI to TBI is appropriate, but there is need for further research, particularly large studies.

As for why DTI is not more readily available, there are likely a number of factors. It currently represents an emerging application for TBI, and is therefore not widely known amongst GPs or even imaging specialists (I've learned this first hand). Further, it requires specific software and a Radiologist capable of properly reviewing the data. Lastly, there seem to be a paucity of imaging places that are currently doing this, even in facilities with 3 Tesla instruments.