The war in Iraq is bringing a well-documented but hardly understood battlefield injury into the limelight: traumatic brain injury (TBI). In an effort to learn more about the injury, the U.S. Army awarded Simbex, of Lebanon, NH, a million-dollar contract to develop sensor-studded helmets for combat soldiers. The army is currently testing the helmet technology, which could be deployed as early as December of this year.

TBI "is going to be the signature injury of the war, and my suspicion is that the consequences are going to far outweigh agent orange from Vietnam," says Kevin Kit Parker, an assistant professor of biomedical engineering at Harvard University, who served with the U.S. Army in southern Afghanistan from 2002 to 2003. The most common cause of TBI is improvised explosive devices (IEDs), which emit shock waves--waves of air pressure--that travel at around 1,000 feet per second, or close to the speed of sound. They also propel fragments of shrapnel that can hit a soldier's helmet with enough force to knock him or her to the ground. While such blasts can cause devastating wounds, and even death, they can also rattle the brain's soft tissue, causing invisible, permanent damage.

Simbex, a research and product-development company that specializes in biomechanical feedback systems, equipped the army's combat helmets with sensors that measure the magnitude, location, and direction of blasts and the pressure changes that occur because of the resulting shock wave. "There are lots of different types of injuries that can be caused by blast events," says Jeff Chu, the vice president of engineering at Simbex, "and we are only measuring two of the parameters that are most associated with shock waves and blast events: the acceleration of the body and pressure."

In tests that should take four to six weeks to complete, the army is comparing the Simbex system with several alternative technologies. The system that performs best is likely to reach the field quickly.

Earlier, Simbex developed a system for measuring the blows sustained by competitors in sporting events, such as football. The technology was acquired in 2004 by Riddell, which uses it in football helmets. (See "A Helmet That Detects Hard Hits.") The combat-helmet system is similar to the one used in football helmets; accelerometers built into the helmet's liner measure the acceleration of a soldier's head. But the army helmets use eight accelerometers, developed by Endevco, whose high bandwidth allows them to measure both high-magnitude and high-frequency impacts. Engineers at Simbex have also equipped the helmets with a pressure transducer to measure the pressure changes caused by the shock wave--another factor that, according to Chu, may be causing brain injuries.