Diffusion Tensor Imaging May Improve Diagnosis and Tracking of Mild Traumatic Brain Injuries

Investigators have found that a state-of-the-art brain imaging method may be useful for detecting and monitoring mild traumatic brain injury, a controversial diagnosis that is based largely on a patient’s subjective experience.

The phrase traumatic brain injury tends to conjure the worst case scenario of a patient who suffers severe brain damage leading to severe disabilities, coma or death.  However, most traumatic brain injuries are classified as mild.  A mild traumatic brain injury typically involves symptoms of brain damage (such as mood changes or confusion), but no sign of damage based on a neurological exam or standard brain imaging techniques.

This definition, or the lack thereof, complicates diagnosis.  Some patients are told nothing is wrong with them.

The lack of objective measures for mild brain injuries also means there is no way to predict their course.  “Although most patients recover completely from their injuries, approximately 5-20 percent of patients do not fully recover.  We need a way to identify those patients early,” said Andrew Mayer, Ph.D., a research scientist at the Mind Research Network and an adjunct assistant professor of neurology at the University of New Mexico in Albuquerque.

In a recent study, Dr. Mayer and colleagues at UNM found that diffusion tensor imaging (DTI) can be used to reliably detect and track brain abnormalities in patients with mild traumatic brain injury.  The study was published in Neurology*, and was supported in part by the National Institute of Neurological Disorders and Stroke (NINDS).

DTI is a version of magnetic resonance imaging (MRI).  It is most useful for visualizing the brain’s white matter, which contains the fibers that connect nerve cells.  DTI is more complicated than MRI in terms of data analysis, but most conventional MRI scanners are equipped to run DTI scans, Dr. Mayer said.

Dr. Mayer and his team used DTI and conventional MRI to examine the brains of 22 patients with mild traumatic brain injury and 21 control subjects.  The two groups were matched for gender, education and age, and were 27 years old on average.  All subjects were given neuropsychological tests to assess their ability to think, emotional state and somatic complaints (such as pain or perceived physical disability).  Patients with mild traumatic brain injury were evaluated within 21 days of trauma, and each had a score of 13-15 on the Glasgow Coma Scale, a 15-point test of motor and verbal functions that is the current standard for diagnosis.

Conventional MRI did not reveal any differences between the patients with mild traumatic brain injury and the controls.  In contrast, DTI revealed white matter abnormalities in the patients, and was better at discriminating patients from controls than were the neuropsychological test results.

To determine if the DTI abnormalities correlated with symptoms of mild traumatic brain injury over time, the researchers asked subjects to return for a second evaluation 3-5 months later.  This is a typical recovery timeframe for mild brain injuries.  At the second visit, patients showed improvements on some of their neuropsychological test results and some of their DTI measures.  Among the control subjects, there was no difference between DTI measures at the first and second visits.

The UNM study helps establish “DTI…as a potential biomarker of injury that may assist in classification and tracking of mild traumatic brain injury and its effects,” according to a commentary by Erin Bigler, Ph.D., of Brigham Young University in Provo, Utah and the University of Utah in Salt Lake City, and Jeffrey Bazarian, M.D., M.P.H., of the University of Rochester School of Medicine in New York.**

Dr. Mayer currently has a grant from NINDS to conduct clinical studies of mild traumatic brain injury that combine DTI with other imaging techniques – such functional MRI and MR spectroscopy.  A grant from NINDS funded through the American Recovery and Reinvestment Act (ARRA) will enable him to pursue similar analyses using magnetoencephalography (MEG).  This is a sensitive technique for measuring the brain’s electrical activity.

“We want to combine information across these imaging modalities to see if we can get a more coherent picture of mild traumatic brain injury, with more power to diagnose it and predict its course,” Dr. Mayer said.

– By Daniel Stimson, Ph.D.

*Mayer, AR et al. “A Prospective Diffusion Tensor Imaging Study in Mild Traumatic Brain Injury.” Neurology, February 23, 2010, Vol. 74, pp. 643-650.

**Bigler, ED and Bazarian, JJ.  “Diffusion Tensor Imaging: A Biomarker for Mild Traumatic Brain Injury?”  Neurology, February 23, 2010, Vol. 74, pp. 626-627.