Different patterns of lesion formation in early and late stages of multiple sclerosis revealed by phase imaging at 7T (P6.115)

Background: Magnetic resonance imaging (MRI) revolutionized the diagnosis of multiple sclerosis (MS), but conventional MR sequences can not always differentiate between early and chronic MS lesions. The analysis of the MR phase provides additional information on the magnetic microstructure and phase contrast changes within MS lesions may reflect different stages of inflammatory activity. However, only limited data are available so far, and the present studies are hampered by limited spatial resolution and small sample sizes of the investigated cohorts. Here we describe lesion morphology in early and late MS lesion stages on high resolving T2* weighted (T2*w), phase, magnitude and susceptibility weighted imaging (SWI) at 7 Tesla (T). Methods: 28 patients (including four clinical isolated syndrome (CIS), 22 relapsing-remitting MS, and two primary-progressive MS patients) were included in this study and subsequently underwent 7T MRI. MS lesions were marked on T2*w images, and subsequently analyzed side-by-side with regard to morphology and visibility on phase, magnitude and SW images. Results: 192 lesions were detected on T2*w images in total. SWI and magnitude visualized the majority of these T2*w lesions (SWI 84.9[percnt]); magnitude 83.3[percnt])). However, only a subgroup of 126 lesions (65.6[percnt]) was characterized by prominent phase shifts and was hence depictable on phase images. Notably, the proportion of lesions characterized by phase abnormalities was higher in patients with early MS (mean±SD 90±19.5[percnt], range 50-100[percnt]) compared to long-lasting MS patients (mean±SD 51±37[percnt], range 0-100[percnt]), p=0.003), and a reduced proportion of phase detectable lesions correlated with a longer disease duration (p=0.001). Conclusion: Phase contrast in MS is disease duration dependent and changes over time due to its sensitivity for structural damage, inflammatory activity, and iron deposits. Thus phase MRI at 7T may be used as a tool to characterize and monitor MS plaque evolution.