NFL concussion: researchers hope blood tests can better detect head trauma

• Several firms trying to develop new methods to assess extent of damage
• Baltimore's Joe Flacco left Miami game with concussion after heavy hit

In the second quarter of an NFL game on Thursday night, the Baltimore Ravens quarterback Joe Flacco slid to gain a first down. The 233lb Miami Dolphins linebacker Kiko Alonso flew into him, ploughing shoulder-first into his head.

Such was the force of the hit, Flacco's helmet flew off. He walked from the field but he was dazed and bleeding from one ear. There was little doubt he had suffered a concussion.