Isotropic 25-Micron 3D Neuroimaging Using Microstructural Manganese-Enhanced MRI (MEMRI).

MRI observations following administration of Mn [manganese (Mn)-enhanced MRI, MEMRI] have been used as an excellent morphological and functional MRI tool for preclinical studies. To detect brain three-dimensional (3D) microstructures, we improved the MEMRI method for mouse brains after Mn administration and obtained high-resolution MRIs using a cryogenic radiofrequency (RF) coil. Male C57BL/6 mice ( = 8) were injected with 50 mM MnCl intravenously and MEMRIs of the brain were acquired after 24 h, followed by perfusion fixation with a 4% paraformaldehyde (PFA) solution. High-resolution 25-μm isotropic MRIs were successfully acquired from the extracted brain tissue and could identify the brain microstructures, especially in the hippocampus [the pyramidal cell layer through CA1-3 and the dentate gyrus (DG) granular layers (GLs)], cell layers of cerebellum, three sub-regions of the deep cerebellar nucleus, and white matter (WM) structures [e.g., the fasciculus retroflexus (fr) and optic tract in the thalamus]. The following technical conditions were also examined: (i) the longitudinal stability of Mn-enhanced tissue after administration; and (ii) the effects of mixing glutaraldehyde (GA) with the fixative solution for the preservation of MEMRI contrast. Our results indicate that MEMRI observations made shortly after fixation maintain the contrast observed . This research will be useful for non-destructive whole-brain pathological analysis.