Magnetic susceptibility contrast variations in multiple sclerosis lesions

Purpose Recent magnetic resonance imaging (MRI) studies have revealed heterogeneous magnetic susceptibility contrasts in multiple sclerosis (MS) lesions. Due to its sensitivity to disease-related iron and myelin changes, magnetic susceptibility-based measures may better reflect some pathological features of MS lesions. Hence, we sought to characterize MS lesions using combined R₂∗ mapping and quantitative susceptibility mapping (QSM). Materials and Methods In all, 306 MS lesions were selected from 24 MS patients who underwent 7T MRI. Maps of R₂∗, frequency, and quantitative susceptibility were calculated using acquired multiecho gradient echo (GRE) phase data. Lesions were categorized based on their image intensity or their anatomical locations. R₂∗ and susceptibility values were quantified in each lesion based on manually drawn lesion masks and compared between lesion groups showing different contrast patterns. Correlations between R₂∗ and susceptibility were also tested in these lesion groups. Results In 38% of selected lesions the frequency map did not show the same contrast pattern as the susceptibility map. While most lesions (93%) showed hypointensity on R₂∗, the susceptibility contrast in lesions varied, with 40% being isointense and 58% being hyperintense in the lesion core. Significant correlations (r = 0.31, P < 0.001) between R₂∗ and susceptibility were found in susceptibility hyperintense lesions, but not in susceptibility isointense lesions. In addition, a higher proportion (74%) of periventricular lesions was found to be susceptibility hyperintense as compared to subcortical (53%) or juxtacortical (38%) lesions. Conclusion Combining R₂∗ and QSM is useful to characterize heterogeneity in MS lesions. J. Magn. Reson. Imaging 2016;43:463-473.