Quantitative Susceptibility Mapping MRI Useful for Measuring Multiple Sclerosis Progression

QSM provides a quantitative way to measure myelin content and iron deposition in the brain—important factors in the physiology of MS.

The research led by Ravi Menon, PhD, a scientist at Western University’s Robarts Research Institute (London, ON, Canada), was published in December 31, 2013, Proceedings of the National Academy of Sciences of the United States of America (PNAS). Dr. Menon and his colleagues including first author David Rudko, tried to determine whether QSM was indeed quantitative. Interpretation of QSM data requires the use of a model of the underlying tissue structure. The scientists found that the most common approach to creating QSM images was in fact ineffective to generate quantitative images—that is, images in which myelin content and iron can be measured.

The researchers demonstrated this by studying the orientation dependence of the MRI signal. This particular signal has typically thought to be a constant, but the team showed that it depends on tissue orientation in both cortical gray and white matter, but not in the deep brain structures such as the basal ganglia. All these areas are implicated in MS.

The investigators demonstrated the discordance between the models for QSM using a device that rotated a rat’s brain so that it could be scanned from 18 different angles, using a 9.4 T MRI scanner. The brains were then sent to histology for comparison. They discovered the values depended on the microstructure of the brain such as myelin concentration and integrity, and iron deposition. The study also revealed, for the first time, the correlation between MRI measurement and histology measurement when the correct model was used.

“With this methodology, we now have a quantitative way to interpret myelin and iron concentrations, and in particular, any changes to them over time,” said Dr. Menon, who holds a Canada research chair in functional MRI. “We’ve been doing these scans on MS patients for a while, but nobody knew if it was a valid approach or not. We now know how to interpret the data. It allows us to separate changes in white matter degeneration, from other changes such as iron deposition, which in conventional imaging all looks the same.”

Dr. Menon reported that the next phase of the research is to use this new imaging approach to study the changes that occur in MS and to find out if it is predictive of disease progression.

Related Links:
Western’s Robarts Research Institute