Two soccer players collide on the field. A soldier in Afghanistan is thrown to the ground during a bomb explosion. A teen has an accident while riding her bike--and she isn't wearing her helmet. Each of these incidents can produce a traumatic brain injury (TBI). Of the 1.7 million Americans officially diagnosed with TBI each year, 52,000 die from their injuries. And that doesn't count all the unreported TBIs, which experts estimate range from about...