Diffusion in dendritic spines: impact on permeative exchange estimation with time-dependent diffusion-weighted MRI

Motivation: Diffusion exchange models NEXI and SMEX assumes permeative exchange between intra- and extra-neurite compartments. Here, we hypothesize fine microstructures, like spines in dendritic segments, without permeable membranes can mimic permeative exchange. Goal(s): We aim to emphasize the significance of taking diffusion-mediated exchange into account when interpreting model-based estimates of exchange in intricate microstructures like the gray matter of the brain. Approach: Monte-Carlo water diffusion simulations in spiny dendritic branches, also featuring undulations and beadingResults: Our results question the way we interpret dMRI exchange estimates, emphasizing the need to exercise caution when inferring these estimates solely as indicators of membrane permeability. Impact: Diffusion exchange models assumes permeative exchange between intra- and extra-neurite compartments. We hypothesize fine microstructures without permeable membranes can mimic permeative exchange. We aim to emphasize considering the impact of intricate microstructures in gray matter when interpreting model-based exchange estimates