Well, TBI isn't called the "invisible injury" for nothing, and, boy, do the insurance companies love that.

Current technology, even FMRI, are not great at imaging brain injury and can offer no real insight into what impacts your damage might be having in your specific case. The best test for that is neuro-psych exam.

Neuro-psychs are, however, expensive, and the insurance company will almost certainly dispute the findings. The latter is especially true if, like most people, you don't have a documented baseline to use as comparison.

Good luck