Quantitative Susceptibility Mapping of Multiple Sclerosis Lesions at Various Ages

Purpose: To assess multiple sclerosis (MS) lesions at various ages by using quantitative susceptibility mapping (QSM) and conventional magnetic resonance (MR) imaging. Materials and Methods: Retrospectively selected were 32 clinically confirmed MS patients (nine men and 23 women; 39.3 years +/- 10.9) who underwent two MR examinations (interval, 0.43 years +/- 0.16) with three-dimensional gradient-echo sequence from August 2011 to August 2012. To estimate the ages of MS lesions, MR examinations performed 0.3-10.6 years before study examinations were studied. Hyperintensity on T2-weighted images was used to define MS lesions. QSM images were reconstructed from gradient-echo data. Susceptibility of MS lesions and temporal rates of change were obtained from QSM images. Lesion susceptibilities were analyzed by t test with intracluster correlation adjustment and Bonferroni correction in multiple comparisons. Results: MR imaging of 32 patients depicted 598 MS lesions, of which 162 lesions (27.1%) in 23 patients were age measurable and six (1.0%) were only visible at QSM. The susceptibilities relative to normal-appearing white matter (NAWM) were 0.53 ppb +/- 6 3.34 for acute enhanced lesions, 38.43 ppb +/- 13.0 (positive; P < .01) for early to intermediately aged nonenhanced lesions, and 4.67 ppb +/- 3.18 for chronic nonenhanced lesions. Temporal rates of susceptibility changes relative to cerebrospinal fluid were 12.49 ppb/ month +/- 3.15 for acute enhanced lesions, 1.27 ppb/ month +/- 2.31 for early to intermediately aged nonenhanced lesions, and -0.004 ppb/ month +/- 0 for chronic nonenhanced lesions. Conclusion: Magnetic susceptibility of MS lesions increased rapidly as it changed from enhanced to nonenhanced, it attained a high susceptibility value relative to NAWM during its initial few years (approximately 4 years), and it gradually dissipated back to susceptibility similar to that of NAWM as it aged, which may provide new insight into pathophysiologic features of MS lesions. (C) RSNA, 2013