Studying brain microstructure in normal ageing using Neurite EXchange Imaging (NEXI) at 500 mT/m

Motivation: Recent quantitative MRI research suggests brain microstructure maturation may be independent of macroscopic structural alterations. NEXI is a novel method probing the water exchange between neurite and extracellular space in grey matter. Goal(s): To observe the age-related alteration of exchange time from NEXI across various grey matter structures. Approach: We acquired in vivo diffusion data on 34 healthy participants on the Connectome 2.0 scanner and compared the measured exchange time between three age groups (18-30; 31-60; 61-79 years). Results: We found older adults have longer exchange time in various grey matter structures, driven by the reduction in neurite to extracellular exchange rate. Impact: This study indicates age-related microstructure alterations may influence the water exchange in grey matter, providing a new imaging phenotype to study neurodegeneration. Developing NEXI normative data will strengthen our understanding of the association between water exchange and neurodegeneration disorders.