Now researchers are experimenting with an imaging technique to detect this damage caused by concussions.
It's a special kind of MRI that measures brain chemicals. Researchers think patients with something called chronic traumatic encephalopathy have altered levels of these chemicals. That may signify damage.
If the chemical changes are a true symptom, then scientists might be able to not only diagnose the condition, but also find ways to treat it.
The research was presented at the Annual Meeting of the Radiological Society of North America.