Brain injuries occult on CT, MR become visible with diffusion tensor imaging

Brain injuries invisible on CT and MRI, and apparent only in cognitive testing, can be revealed with diffusion tensor imaging, a study concludes.

Each year there are more than 1.1 million cases of mild traumatic brain trauma reported in the U.S., according to the Centers for Disease Control and Prevention. Of those patients, as many as 30% have permanent impairment and 20% are unable to return to work.

Mild traumatic brain injury is diagnosed based on history and clinical examination because CT and MR results typically come back normal. However, diffusion tensor imaging (DTI) can detect frontal white matter injury, demonstrating whether patients have sustained impairment to the brain, according to researchers at Albert Einstein College of Medicine in the Bronx.

DTI uses MRI to determine the direction and magnitude of water diffusion.

In the study, DTI found 15 clusters in 20 patients in which white matter fractional anisotropy was lower compared with that of controls (Radiol 2009;252:816-824). Five of these clusters were located in the frontal lobe. Anisotropy is a measure that reflects directional organization of white matter tracts and is influenced by their magnitude and orientation.

Analysis also demonstrated lower fractional anisotropy is associated with poorer cognitive function.

The dorsolateral prefrontal cortex is most commonly impaired after mild brain injury and is a major contributor to disability, since executive function is dependent on the site, said Dr. Michael L. Lipton, the director of radiology research at Albert Einstein College and lead author of the study.

Patients with damage to their dorsolateral prefrontal cortex had trouble with activities such as completing a computerized maze and performance tasks.

"A major problem in minor traumatic brain injury clinical management today is that there is no diagnostic test to confirm or rule out the presence of injury," Lipton said.

This study seeks to remedy that.

DTI could be used to detect evidence of injury and to triage patients for more intensive follow-up and rehabilitation, he said. Or patients with no evidence of injury could be reassured.

"It would not be possible at present to use DTI at the time of injury in a combat zone, but that might be in the future," Lipton said. "DTI could also be employed after return from combat to assess persistent symptoms."

Persistent symptoms crop up in athletes due to repetitive trauma, and DTI could be used in the future to determine whether it was safe to play after an injury, Lipton said.

It remains to be seen whether DTI findings at the time of injury are predictive of long-term outcomes; larger longitudinal studies are needed, Lipton writes in the study.

It is also important to note the study's findings required specialized quantitative assessment of the images, Lipton said.

"You cannot see the findings-as significant as they are-on visual inspection," he said.

Translating DTI for mild traumatic brain injury to clinical practice will require means to make similar quantitative assessments for other clinicians, according to Lipton.