Quantifying features of human gray matter microstructure postmortem using Neurite Exchange Imaging (NEXI) at ultra-high field

In this work, we characterized microstructure properties of cortical gray matter and hippocampus using diffusion MRI, on two samples of postmortem fixed healthy human brain. The weak-to-absent diffusivity time-dependence and marked kurtosis time-dependence supported the suitability of the Neurite Exchange Imaging (NEXI) model to probe postmortem human gray matter microstructure. NEXI parametric estimations revealed region-specific values, calling for further validation using histology and further clarifying the discrepancy between compartment diffusivities estimated here vs. the literature. This study offers an important window on human gray matter microstructure at a spatial resolution unachievable in vivo.