MRS Shows Differences in Postinjury Brain Metabolism


PHOENIX — Measurement of N-acetylaspartate with magnetic resonance spectroscopy shows regional differences in brain metabolism after traumatic injury, according to a report at a congress of the Society of Critical Care Medicine.

Paul M. Vespa, M.D., director of neurocritical care at the University of California, Los Angeles, described the ongoing observational study being done by neurosurgeons in the university's brain injury research center.

He reported that N-acetylaspartate (NAA) levels were most reduced in the area of the brain with the most damage (P = .0001), but he noted that other areas also showed effects.

“Even normal-appearing brain regions have low NAA,” he said, showing a skull-like image he called a “phantom replacement model.”

Circles that looked like ping-pong balls represented different concentrations of NAA and filled the model, which was matched with microdialysis.

“You can determine a map of NAA and get actual NAA values throughout the brain,” he said.

NAA is a metabolic marker for mitochondrial dysfunction and corresponded to elevated lactate/pyruvate levels, another sign of distress, in 20 patients studied so far, according to Dr. Vespa. The lowest levels were seen in patients with the longest duration of high lactate/pyruvate levels, he said.

As described by Dr. Vespa, measuring NAA with magnetic resonance spectroscopy (MRS) holds promise as a noninvasive way of assessing damage to areas of the brain missed by microdialysis monitoring.

Microdialysis has the advantage of being continuous, he said, but it only allows a small section to be monitored. MRS can take a picture of the whole brain, he continued, but it can only be used once daily at most and usually only once per hospitalization.

“It [MRS] will be done as a snapshot,” he said. “It won't be a monitor, but it will be an image of the whole brain. And you will be able to know whether certain segments of the brain are at risk.”

The technology is currently available and in clinical use with brain tumors, according to Dr. Vespa. Before MRS measurements of NAA can be used in assessing traumatic brain injury, these findings need to be confirmed by studies comparing findings to the cerebral metabolic rate of oxygen, he said, adding that those studies are in progress.