Quantitative susceptibility MRI better identifies MS

Quantitative susceptibility (QS) MRI can better distinguish and track multiple sclerosis (MS), according to a study published online May 14 by Radiology.

Standard MRI measures of MS disease status that use the number and location of lesions in white matter are troublesome, as they don’t correlate well with clinical symptoms or significantly predict disease progression.

“When you do conventional MRIs on these patients you see lesions in the brain very clearly, but the number or volume of their lesions do not correlate with the patients’ disabilities,” said the study’s senior author, Ravi S. Menon, PhD, of the University of Western Ontario in Canada, in a press release. “This paradox has been recognized since the MRI was introduced to clinical practice in the early 80s, and yet this is the only imaging tool we have for assessing MS.”

R2* has been proposed to be a surrogate biomarker for disease severity, but R2* mapping can be inaccurate. QS mapping is complementary to R2* mapping, which Menon, lead author David A. Rudko, PhD, and colleagues took into consideration for their study. They investigated the utility of QS-based MRI at 7-T in identifying characteristic regions indicative of demyelination and increased iron deposition in patients with MS and their relation to patient disability.

Twenty-five patients with clinically isolated syndrome (CIS) or relapsing-remitting MS were involved in the study. Quantitative maps of the MRI susceptibility parameters, R2* and QS, were computed for the cohort. Fifteen age and sex-matched control subjects were also imaged at 7-T. The candidate MRI biomarkers were then correlated with the Extended Disability Status Scale (EDSS), time since CIS diagnosis, time since MS diagnosis and age.

The QS maps helped identify significant, voxel-level increases in iron deposition in subcortical gray matter of patients with MS in comparison to the control subjects. However, these voxel-level increases were not seen on R2* maps.

Once region-of-interest analysis of mean R2* and QS in subcortical gray matter was performed, it was revealed that R2* and QS were both strongly correlated with EDSS. The total volume of white matter damage on QS maps significantly correlated with EDSS. Age-adjusted clinical scores could also offer more robust measures of MS disease severity than non-age-adjusted scores, as voxelwise QS supported a significant contribution of age to demyelination in patients with MS.

“Using this information may allow earlier administration of therapies and monitoring of MS pathologic process in vivo,” wrote Rudko and colleagues. “The sensitivity of both QS and R2* mapping to total white matter  (lesions plus normal appearing white matter) damage suggests that these quantitative image contrasts may be useful for long-term monitoring of demyelination and remyelination in MS,” they concluded.