A PET scan will not show the microscopic damage from a concussion.

An fMRI may show some problems. Functional MRI works by showing the areas of the brain that get activated during thinking processes. They are mostly still used in research.

I have had CT, MRI, MRI/MRA, and SPECT ( more specific form of a PET). Despite symptoms from a lifetime of concussions and permanent Post Concussion Syndrome/Multiple Concussion Syndrome symptoms, all of the images were negative.

The only diagnostic that showed concussion damage was a qEEG. I have had three qEEGs and they all show the same kind of damage, even the last qEEG that was 6 years after the injury. There are a few good mTBI and TBI databases that are used to compare qEEG results that have a specific accuracy of 95 to 98%.

Unfortunately, there are many who have worked hard to discredit qEEG as a valid diagnostic tool by using limited data sets to support their conclusions. It appears that the pharmaceutical industry and personal injury liability insurance industry are doing a good job at protecting their interests.