A new technique for analyzing MRI data, developed by researchers at UT Southwestern Medical Center in Dallas, can reveal serious brain injury missed by current tests and help predict a patient’s degree of recovery.
In abrupt head trauma, the force can shear and damage nerve cells—an injury that does not show up on CT scans and MRI does not yet reliably detect, the researchers said.
“This is a new way of measuring a common injury that has been overlooked,” said Ramón Díaz-Arrastia, MD, PhD, professor of neurology and senior author of the paper, which appears in the May issue of the Archives of Neurology.
“No matter how many seat belts and airbags there are, if you hit a tree at 50 miles an hour, you’re going to have this kind of injury,” Díaz-Arrastia said. “It may account for up to half of the traumatic brain injuries from car accidents.”
The injury typically affects the portions of nerve cells in the brain called the axons, the long, thin extensions of nerve cells that reach from one area to another. When the brain is subjected to powerful, inertial forces, axons can be deformed and damaged. This type of trauma, called diffuse axonal injury (DAI) is often difficult to diagnose, Díaz-Arrastia said.
In the study, the researchers performed MRI analysis on 12 people, ranging in age from 16 to 37, who had severe, closed-head brain injury, who were either able to give consent or whose legal guardians gave consent.
From the patients’ point of view, the test was the same as undergoing an ordinary MRI. The difference was that the researchers used a new mathematical analysis, called diffusion tensor tractography, to detect diffuse axonal injury. They also analyzed the MRI data using an existing method called fluid attenuation and inversion recovery (FLAIR).
The new analysis tested for how easily water could move around in the brain in the areas surrounding cells. When the axons are damaged, they swell, absorbing the water around them and leaving less that can move around between cells. As the axons die, they release the water, resulting in more water surrounding the cells, Díaz-Arrastia said.
By comparing multiple MRI images over time, focusing on three areas of the brain – the corpus callosum, the fornix and the peduncular projections—the researchers said they were able to detect a change in water motion.
The researchers tested the patients’ degree of consciousness and ability to care for themselves immediately after their injuries, as well as six to 11 months later. One patient died, and one had fully recovered, with the rest showing partial recovery. One patient could not be located for the follow-up.
In most of the brain areas studied, the degree of DAI, which is reflected by a reduction of the motion of water around the nerve cells, was significantly linked to how much the patients improved over time, the researchers found. In contrast, FLAIR analysis did not show a statistically significant link with the degree of recovery, according to the researchers.
Díaz-Arrastia and colleagues plan to study other areas of the brain that are at risk for diffuse axonal injury to see whether MRI analysis can be useful in those regions as well.
The National Institute on Disability and Rehabilitation Research and the National Institutes of Health funded the study.