Diffusion tensor imaging (DTI) could allow researchers to estimate three months in advance the chronic effects of inflammation of the optic nerve—a condition which often occurs as a result of multiple sclerosis (MS)—according to research published online Dec. 16 in Neurology.
“We see this as part of a battery of tests we hope to give patients within the next decade to help our clinical assessment and tailor it to an optimal treatment,” said lead author Robert T. Naismith, MD, assistant professor of neurology and a physician at Barnes-Jewish Hospital in St. Louis, Mo. “It may also help further refine our basic understanding of MS in terms of expanding our insights into where and how damage occurs and why it can affect patients differently.”
Regular MRI scans can detect optic neuritis but offer no information on its severity and potential lasting consequences for a patient's vision, according to the authors.
Currently in use clinically to detect and follow up on strokes, the researchers said that DTI uses a rapid series of MRI scans to track water diffusion in tissue. Noting that inflammation and the cell damage it causes would likely alter water diffusion in the affected tissues, Naismith and colleagues hypothesized that this information might allow them to assess the severity and potential for lasting damage of MS flare-ups.
Over the past five years, the paper’s senior authors, Sheng-Kwei Song, PhD, associate professor of radiology, and Anne Cross, MD, professor of radiology, did much of the quantitative work in animal models of MS. The new data, based upon the successful collaborative history, are the first to show that DTI can produce potentially useful predictive information in humans.
Researchers used DTI to image the optic nerves of 12 healthy volunteers, 12 patients who had begun to suffer from optic neuritis within the past month and 28 patients with a history of earlier outbreaks. They gave participants with optic neuritis or a history of it detailed assessments of their visual health, including tests of visual acuity and the thickness and conductivity of their optic nerves.
The researchers reported that DTI scans showed that the water diffusion along the length of the subjects' optic nerves, a characteristic known as axial diffusivity, averaged about 1.66 micrometers squared per millisecond. In three patients with acute optic neuritis, those levels went down as much as 0.45 micrometers squared per millisecond.
“As the inflammation breaks down the structure of the axons or branches of the optic nerves, the normal water diffusion in this direction is impeded,” Naismith explained. “After several months, though, the debris is cleared away, and this value and another characteristic known as radial diffusivity, then start to increase.”
“The next step is taking the technique into the brain and spinal cord, where there are many different streets crossing. Measuring damage and correlating it to dysfunction will be more complex as a result,” he said.