Whether it's football, basketball, hockey, even soccer: concussions are hard to avoid.
The CDC estimates that every year, almost four million people get them. Many others get what's called a sub-clinical concussion, a hit to the head that less seriously affects the player but still causes problems in the brain.
Now, researchers at the Radiological Society of North America, who are meeting here in, Chicago say they may have taken a first step towards treating players who've had so many concussions that they've begun having memory and behavior problems.
Up until now, this kind of brain degeneration could only be diagnosed by a pathologist, looking at the brain of the athlete during an autopsy.
But using a special kind of MRI called magnetic resonance spectroscopy, researchers from Brigham and Women's Hospital in Boston say they've been able to do what they call a "virtual biopsy" on a living patient.
They scanned the brains of five former pro athletes and compared them to scans of otherwise healthy non athletes and they discovered chemical changes in the former athletes brains that didn't show up in the other subjects.
If further studies show this to be an effective way to identify the kind of brain damage that leads to long term disability, then doctors say it could have broad applications.
Dr. Alexander Lin says being able to diagnose it "could help athletes of all ages and levels, ,as well as war veterans who suffer mild brain injuries, many of which go undetected."
Ultimately, if the brain changes are chemical, there's speculation that drugs could be created that would affect those chemicals, and perhaps slow or even stop the brain from degenerating.