7 Tesla Magnetic Resonance Imaging to Detect Cortical Pathology in Multiple Sclerosis

BACKGROUND Neocortical lesions (NLs) are an important pathological component of multiple sclerosis (MS), but their visualization by magnetic resonance imaging (MRI) remains challenging. OBJECTIVES We aimed at assessing the sensitivity of multi echo gradient echo (ME-GRE) T2*-weighted MRI at 7.0 Tesla in depicting NLs compared to myelin and iron staining. METHODS Samples from two MS patients were imaged post mortem using a whole body 7 T MRI scanner with a 24-channel receive-only array. Isotropic 200 micron resolution images with varying T2* weighting were reconstructed from the ME-GRE data and converted into R2* maps. Immunohistochemical staining for myelin (proteolipid protein, PLP) and diaminobenzidine-enhanced Turnbull blue staining for iron were performed. RESULTS Prospective and retrospective sensitivities of MRI for the detection of NLs were 48% and 67% respectively. We observed MRI maps detecting only a small portion of 20 subpial NLs extending over large cortical areas on PLP stainings. No MRI signal changes suggestive of iron accumulation in NLs were observed. Conversely, R2* maps indicated iron loss in NLs, which was confirmed by histological quantification. CONCLUSIONS High-resolution post mortem imaging using R2* and magnitude maps permits detection of focal NLs. However, disclosing extensive subpial demyelination with MRI remains challenging.