New research being presented at the annual meeting of the Radiological Society of North America (RSNA) in Chicago, IL, this week shows how a highly sensitive type of magnetic resonance imaging (MRI) can reveal the long-term impact of blast-induced brain injuries in soldiers.
Called diffusion tensor imaging (DTI), the MRI method identifies tiny injuries in the structure of white matter in the brain. White matter consists almost entirely of signal-carrying nerve fibers or axons. Damage to these axons changes the way water moves along them, and this is what DTI can pick up.
One of the researchers, Thomas M. Malone, of the Saint Louis University School of Medicine, compares it with what happens to a damaged garden hose:
"As water passes through the hose from the faucet to the sprinkler, it goes in the same direction, but if you were to puncture the hose with a rake, the water would shoot out the sides."
The DTI method yields a measure called "fractional anisotropy" (FA) that can be used to assess the extent to which the water is diffusing in all directions, instead of just moving in one direction along the nerve fiber. A low value usually indicates more injury.
Estimates suggest that around one in five US soldiers returning from recent wars has blast-induced mild traumatic brain injury (MTBI), which can be difficult to diagnose. Standard imaging systems, such as CT and normal MRI, often do not spot it.
For their study, the team compared FA values from DTI scans of 10 veterans diagnosed with MTBI who had served in Iraq with that of 10 healthy controls.
The average time that had passed between the veterans suffering blast-induced injury and undergoing DTI scans was over 4 years.
First study to use DTI to measure MTBI years after blast
This long timescale is a unique feature of the study, say the researchers - other studies of blast-related MTBI have tended to examine patients much closer to the time of injury.
The results showed significant differences between the FA values of the healthy controls and the veterans diagnosed with MTBI.
The researchers also found significant links between FA values and measures of attention, delayed memory and psychomotor test scores.
As more than 4 years had passed since the veterans had been exposed to the blasts, the researchers say their study shows the presence of a long-term impact of blast injury on the brain.
This may explain the ongoing cognitive and behavior symptoms seen in some veterans with a history of blast-related MTBI, they add.
The study also indicates that DTI can show differences in blast-related MTBI between groups, even years after the injury, as co-author P. Tyler Roskos, a neuropsychologist and assistant research professor at Saint Louis University School of Medicine, explains:
"DTI shows promise in enhanced sensitivity for detecting MTBI compared to MRI/CT, even in the chronic phase. Identification of changes in specific brain regions may help in diagnosis and treatment of MTBI among veterans."
Prof. Roskos says they conducted the study to help doctors find better ways to distinguish between MTBI and PTSD in veterans:
"It makes a difference, because PTSD is psychological in nature and MTBI is neurological. Many veterans in the health care system are dealing with MTBI, PTSD or both. Our emphasis today is to find the best treatments and measure the patient's progress. Imaging has the potential to do that."
The study follows another published earlier this year in the American Journal of Psychiatry that also used DTI to identify brain abnormalities in veterans with MTBI.