A new MR technique called macromolecular proton fraction (MPF) mapping revealed that patients with multiple sclerosis (MS) lose myelin — the fatty protective sheath around nerve fibers — in the gray matter of their brains, and it's closely related to how severe the disease is, according to a recent study published online in the journal Radiology.

MS was previously thought to be a disease that affected the brain's white matter because myelin is more prevalent there. But there is actually also a small quantity of it in gray matter. Even though it's only a small amount, it's now known that it plays a vital role in protecting the thin nerve fibers that connect the neighboring areas of the brain cortex.

The new MR technique works by gathering information on the amount of biological macromolecules — the molecules in tissues that consist of a large number of atoms including proteins, lipids and carbohydrates. It was inconvenient to perform it in the past because it took a long time to collect the data, but now improvements have been made to make it much faster.
The only thing needed for the technique is a standard MR scanner and only a few software modifications are required. Right now, it's the only method to evaluate the amount of myelin in gray matter.

Researchers at the University of Washington had 30 MS patients — 18 with relapsing-remitting MS (RRMS) and 12 with secondary progressive MS (SPMS), which is the more advanced form, — and 14 healthy control patients undergo scans on a 3-Tesla MR.

They reconstructed 3-D whole-brain MPF maps in order to evaluate the white matter, gray matter and MS lesions. They then compared their results with clinical tests characterizing neurological dysfunction in MS patients.

They found that MPF was much lower in white and gray matter in RRMS patients than in the healthy patients and it was also much lower in normal-appearing brain tissues and lesions of SPMS patients than in RRMS patients.

They also found that the amount of MPF in brain tissues is largely connected to clinical disability and the strongest associations were found for gray matter.

The researchers believe that this new technique may have important applications for MS treatments targeted to protect and restore myelin. It could potentially provide an objective measurement of MS progression and how successful treatment is in clinical trials.

"Assessment of both gray and white matter damage with this method may become an individual patient management tool in the future," Dr. Vasily L. Yarnykh, associate professor in the radiology department at the university, said in a statement.

The researchers are continuing to conduct more research on the new technique with the support of the National Multiple Sclerosis Society and the National Institutes of Health.

They're going to compare MS patients with control patients in order to find out how the amount of myelin changes over time. They eventually want to use the technique for spinal cord imaging to see if the combined assessment of demyelination in the brain and spinal cord could better explain disability progression.

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