Each year, thousands of Americans suffer a traumatic brain injury. In 2013, about 2.8 million TBI-related emergency department visits, hospitalizations and deaths occurred in the United States, according to the Centers for Disease Control and Prevention. Most of these are what are called mild traumatic brain injuries, or mTBIs — head injuries that don't cause a coma. People with an mTBI typically get better within a few weeks, but for as many as 20 percent, problems can linger for months or years.