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Diffusion Tensor Imaging May Shed Light on Soldiers' Brain Injuries

For release: Wednesday, July 13, 2011

More than a hundred thousand soldiers have returned from combat in the Middle East with traumatic brain injuries, many of which are described as "mild" despite devastating consequences.  Inability to concentrate, memory loss, sleep disturbances and depression are common symptoms.  These mild injuries, however, are difficult to see on brain scans, raising a host of questions about how to diagnose and treat them.

DTI scan of a control subject. Modified from Mac Donald et al. NEJM, 2011 Supplementary Appendix.
DTI scan of a control subject in the study, looking down on the brain from above. Modified from Mac Donald et al. NEJM, 2011 Supplementary Appendix.

A brain scanning method called diffusion tensor imaging (DTI) could one day help resolve these issues.  In a new study, military and academic researchers used DTI to examine dozens of soldiers diagnosed with mild traumatic brain injury while serving in Iraq and Afghanistan.  While conventional brain scans appeared normal in all but one of the soldiers, the DTI scans detected clear signs of brain damage in about one-third.

Researchers from Washington University School of Medicine in St. Louis lived on and off in Landstuhl, Germany for two years, and worked closely with doctors at an American military hospital there.  The team reported their findings in the New England Journal of Medicine.*

All the soldiers in the study had been injured by an explosion or concussive blast.  By definition, a mild traumatic brain injury typically involves symptoms of brain damage but no sign of damage based on a neurological exam.  Standard brain scans of such injuries, using computerized tomography (CT) or magnetic resonance imaging (MRI), usually look normal.  This makes it difficult to determine what parts of the brain have been damaged, how the damage might evolve with time, and what types of rehabilitation might help.

Researchers suspect that in mild traumatic brain injury, the damage primarily affects the delicate tracts of nerve fibers that run through the brain and connect different regions.  DTI, developed by scientists at the National Institutes of Health, is a relatively new MRI-based method that enables researchers to see these fiber tracts.  It has shown promise for helping diagnose and monitor brain injuries from non-combat trauma, such as auto accidents and falls.

This is the first time that researchers have used DTI to examine and follow active-duty soldiers with mild traumatic brain injury.  The study is also unique in its focus on blast-related brain injury, which has been described as the signature wound of the wars in Iraq and Afghanistan, and is commonly linked to improvised explosive devices (IEDs).

The researchers studied 63 soldiers with mild, blast-related traumatic brain injuries and 21 soldiers who had been exposed to blasts but did not suffer brain injuries.  In 2008 and 2009, the soldiers had DTI scans at Landstuhl Regional Medical Center in Germany, a central triage point where injured troops get care that is not available in Iraq or Afghanistan.  The scans focused on 17 brain regions predicted to be vulnerable to blasts based on computer simulations.

DTI scans show thinning of tracts in the orbitofrontal white matter. Modified from Mac Donald et al. NEJM, 2011 Supplementary Appendix.
These DTI and MRI scans focus on an area called the orbitofrontal white matter in a control subject (left) and a solider with mild traumatic brain injury (right). The DTI scans (top) show thinning of fiber tracts in this area (arrows). Modified from Mac Donald et al. NEJM, 2011 Supplementary Appendix.

Eighteen of the 63 soldiers with mild traumatic brain injury had definite signs of brain damage, meaning that the DTI scans found abnormalities in at least two or more brain regions.  Twenty of the soldiers had one abnormality on DTI, some of which the researchers say could have occurred by chance.  The other 25 had no abnormalities.  Many of the soldiers received follow-up scans within 6-12 months, which showed that the results were consistent over time.

"DTI will never replace a clinical evaluation, but we hope that it will become a useful tool for diagnosis and for guiding rehabilitation," said Christine Mac Donald, Ph.D., the study's first author and a research instructor in neurology at Washington University. 

It is unclear why the DTI scans found no signs of brain damage in more than two-thirds of the soldiers, despite the fact they all were diagnosed with mild traumatic brain injuries.  Ongoing studies are addressing this issue, Dr. Mac Donald said.

Another question is whether blast-related brain injuries are different from brain injuries caused by other, more common kinds of trauma such as auto accidents, falls and other blunt object injuries to the head.  A blast can cause blunt injuries, but it also produces a shockwave that can pass through the skull to the brain.

In this study, all of the soldiers with brain injuries had experienced a blast plus head trauma from a fall, vehicle crash, or shrapnel.  So, Dr. Mac Donald and her colleagues were not able to address the effects of pure blast injury.

This first report represents the beginning of an important collaboration between academic and military researchers, Dr. Mac Donald said.  "We were the first academic scientists to set foot at Landstuhl," she said of the Washington University team.  "They had a need to better understand what was happening to their soldiers, while we had state-of-the-art brain imaging methods but no way to study blast injuries in an acute care setting."

The principal investigator was David Brody, M.D., Ph.D., an assistant professor of neurology at Washington University.  Stephen Flaherty, M.D., former chief of trauma surgery at Landstuhl Regional Medical Center, was also a senior author.

In ongoing work, the researchers are using DTI to examine a larger number of soldiers with diverse types of brain injury.  They are looking at additional brain regions for signs of damage, and probing the link between combat-related brain injuries and post-traumatic stress disorder.

This research is supported by the Congressionally Directed Medical Research Program of the Department of Defense, and NIH's National Institute of Neurological Disorders and Stroke.

-By Daniel Stimson, Ph.D.

*Mac Donald C et al.  "Detection of Blast-Related Traumatic Brain Injury in U.S. Military Personnel," New England Journal of Medicine, published online June 2, 2011.

Last Modified February 1, 2013