Purpose: To investigate changes in magnetic resonance imaging (MRI) indices following formalin fixation of postmortem multiple sclerosis (MS) cortical gray matter (CGM). Postmortem MS brain is being used to establish pathological correlates of changes detected using MRI, with recent emphasis on CGM. Fixation induces tissue alterations that may confound inference of in vivo observations from MRI/histology correlation studies.
Materials and Methods: T 2 -weighted scans were obtained alongside quantitative T 1 , magnetization transfer ratio (MTR), and macromolecular proton fraction (f B ) measurements before and after formalin fixation of 15 postmortem brain samples. Type and size of CGM lesions (CGML) was identified on sections immunostained for myelin basic protein.
Results: MRI indices obtained in unfixed MS CGM were similar to values obtained in subjects with MS in vivo. Fixation led to reduction in T 1 (617 msec [standard deviation ¼ 114] vs. 1156 msec [216]) and MTR (24.1 [3.3] percent units [pu] vs. 29.1 [2.5] pu) and increase in f B (5.4 [0.7] pu vs. 3.2 [2.3] pu) (all P < 0.01). The proportion of CGM affected by demyelination did not alter the MRI data. Conclusion: MRI indices in the CGM are significantly altered following tissue fixation.