New imaging techniques could detect subtle brain injuries

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Researchers have shown that three new imaging techniques can detect mild brain damage not visible using traditional methods, which could help scientists better define the type of damage that can lead to long-lasting memory and emotional problems, as well as help identify those who are most vulnerable to further trauma, according to research presented this week at the Society for Neurosciences conference in Washington, D.C.

Scientists have hypothesized that mild head trauma damages the brain's white matter, which is invisible to CT scans and MRI. One of the new techniques for detecting subtle brain injury, called diffusion tensor imaging (DTI), is a variation of MRI that tracks water molecules in the brain's white matter.

David Brody, a neurologist and scientist at Washington University, in St. Louis, and colleagues found that DTI analysis of brain-injury patients revealed signs of white-matter damage not visible with normal MRI. The damage seemed to correlate with cognitive deficits, including slowed reaction time.

A second variation of MRI, known as MR spectroscopic imaging (MRSI), can analyze the spectral frequencies of chemicals in the body. Andrew Maudsley and his colleagues at the University of Miami have used new advances in MRI technology, including higher-strength magnets, to develop MRSI methods that can measure concentrations: n-acetylaspartate (NAA), a marker of white-matter density and choline, which has been linked to injury.

The researchers found decreases in NAA, possibly due to damaged axons, and increases in choline in a group of 25 patients with traumatic brain injury, according to Maudsley, who presented the work at the conference.

A third imaging study presented found that changes to slow-wave activity, which have been previously linked to traumatic brain injury, are likely caused by damage to the white matter. Mingxiong Huang and his colleagues used magnetoencephalography (MEG), which measures the magnetic fields produced by the electrical activity of nerve cells, to pinpoint the source of abnormal brain activity, and they discovered that it often overlapped with the location of damage detected using DTI.

While the research is promising, moving the new imaging techniques into clinical use is likely to be a challenge. "The bar for clinical diagnosis of individual patients is different than for measuring a group effect," said David Moore, a neurologist at Walter Reed Army Medical Center in Washington, D.C. Physicians would need to be able to detect brain changes characteristic of injury on an individual level.

Both DTI and MRSI can be performed using most standard MRI machines, but they require much more extensive data analysis than most medical imaging, something that radiologists aren't used to providing, said Brody. MEG, which is used to pinpoint seizures in epilepsy patients, is even more complicated, and the machines are still quite rare in clinical centers, he added.