A sophisticated imaging technique has revealed signs of brain injury in soldiers injured in explosions. The injuries, which don’t show up with standard imaging techniques, may help explain why some soldiers suffer long-term problems after such injuries.

Brain injuries caused by blasts from improvised explosive devices, rocket-propellant grenades, or land mines in Iraq and Afghanistan are a major concern for the U.S. military. An estimated 10 to 20 percent of all deployed troops have experienced mild traumatic brain injuries as a result of such blasts. And although these injuries are linked to long-term psychological and mental problems, medical experts lack the means to detect any resulting physical damage.

A study by researchers at the Washington University School of Medicine in St. Louis and the U.S. military found that damage to the brain can be detected using an advanced form of magnetic resonance imaging (MRI) called diffusion tensor imaging (DTI). This technique tracks the movement of water molecules through the brain, providing a detailed picture of the brain’s white matter—the neural wiring that connects cells. Damage to this tissue has long been associated with mild traumatic brain injury.

The researchers studied 63 soldiers who were diagnosed with traumatic brain injury after being injured in explosions in Iraq and Afghanistan. The diagnosis was based on such symptoms as loss of consciousness, confusion, and headaches. Standard imaging methods, including MRI and CT, did not show any brain injury in most cases. The researchers studied the soldiers within 90 days of admission to the Landstuhl Regional Medical Center in Germany, and again six to 12 months later.

In the study, conducted from 2008 to 2009 and published June 2 in the New England Journal of Medicine, the researchers found that 18 of the 63 subjects diagnosed with traumatic brain injury had abnormalities in the white matter in two or more regions of the brain. A further 20 subjects had abnormalities in one area, and 25 had none. The abnormalities were also consistent with computer simulations of the likely effect of explosions on the brain.

“The significance of the new study is that it contains data across time,” says David Moore, a professor of neurology at Tulane University School of Medicine in Louisiana and the former deputy director of the Defense and Veterans Brain Injury Center in Washington, D.C. “A year later, the DTI findings showed there were still abnormalities in the brain’s white matter, suggesting that this type of injury can have long-lasting effects.”

Moore conducted a similar study at the Walter Reed Army Hospital in 2009, using DTI to study the brains of injured U.S. military personnel, on average about 80 days after a blast event. This study also showed damage to the brain’s white matter; the results are expected to be published in the next months.

“DTI is very sensitive to the diffusion of water, which, in organized tissues, moves more readily along the axon,” says Christine Mac Donald, a research instructor in neurology at Washington University and director of the study. “We used the water diffusion patterns along these tracks to infer changes that represent axonal injury,” says Mac Donald. The researchers also examined 21 control subjects—men exposed to blasts recently but with no symptoms of concussions.

All the men in the study had experienced what’s known as a “blast-plus” event, meaning they experienced the rapid pressure wave of a blast and had blunt trauma to the head. On average, the subjects were studied 14 days after they were admitted to Landstuhl Regional Medical Center. A second evaluation took place in the U.S. within a year. The second scan showed persistent abnormalities that were consistent with evolving injuries.

Mac Donald, who conducted the study with principal investigator David Brody, an assistant professor of neurology at Washington University, says the study is a first step in determining the pathology of traumatic brain injury, and in being able to diagnose the injury.

Barclay Morrison, an associate professor of biomedical engineering at Columbia University, says subtle structural damage to the brain after a blast is tough to detect, but that is what affects cognitive functions like sleep, memory, and planning. However, while DTI was able to detect most of these subtle changes, it is too early to correlate the damage with behaviors. “Now that we have a way to identify the injury, the next step is to find the underlying injury mechanism—what is happening to the white matter?”

David Hovda, director of the Brain Injury Research at the University of California, Los Angeles, says the study opens up a gateway for the military to make progress in understanding and treating traumatic brain injury. “For many years, traumatic brain injury was an underappreciated problem, a silent epidemic around the world. Now we can say these symptoms are real, and we have an imaging technique to prove it,” says Hovda.

Mac Donald says DTI could be implemented in hospitals or medical stations fairly easily. It uses an MRI machine and requires an upgrade to the software but no additional hardware.

There is still more research to be done, though. “We are looking at a larger group of patients and trying to shed light on the relationship between these findings and functional outcome—what does it mean for me as a patient? What does it tell the doctor about how to treat me or my symptoms?” Mac Donald says.