Comparison of T1- and T2-weighted MRI contrasts of ex vivo ex situ brains fixed with solutions used in gross anatomy laboratories

Post-mortem magnetic resonance imaging (MRI) offers high resolution and histological correlation, so protocols have been developed by brain banks using hemispheres fixed by immersion in Neutral-buffered formalin (NBF), but they provide limited tissue samples. Conversely, anatomy laboratories could supply complete brains perfused either with a salt-saturated (SSS) or an alcohol-formaldehyde (AFS) solution. These fixation methods alter the brains molecular properties, potentially affecting MRI quality and structural characteristics. T1- and T2-weighted (T1w, T2w) contrasts change with NBF fixation, but the effects of SSS or AFS remain unknown. We compared T1w and T2w intensities of different regions of interest (ROIs), including subcortical white matter (WM), cortical and deep gray matter (GM), in brains fixed with NBF, SSS and AFS. We scanned 20 ex situ hemispheres (NBF-immersed=7; SSS-perfused=7; AFS-perfused=6) in a 3T MRI scanner using T1w (0.7mm3) and T2w (0.64mm3) sequences overnight. Mean intensities of 29 ROIs in T1w and T2w MRIs and GM-WM ratios were calculated and compared in brains fixed with the three solutions. We found that T1w images were more affected by the fixation process, inverting the contrast of in vivo T1w and reducing the GM-WM contrast in AFS-fixed brains. T2w images resembled in vivo scans and maintained a sharp contrast in brains fixed with the three solutions, although the GM-WM intensity ratios were lowered in SSS-fixed brains. In conclusion, brains fixed with SSS and AFS from anatomy laboratories could be used for MRI studies, especially with the T2w sequence that seems more appropriate for structural analyses in different ROIs.