Ultra-high gradient diffusion MRI on Connectome 2.0 reveals time-dependent diffusion and water exchange in human gray matter

Motivation: In vivo mapping of exchange between intra-neurite and extracellular water in gray matter is challenging, as the required strong diffusion weighting significantly reduces the signal-to-noise ratio. Goal(s): We aim to demonstrate the feasibility of in vivo neurite exchange imaging using the state-of-the-art Connectome 2.0 scanner equipped with high-performance gradient system (Gmax=500mT/m, (dG/dt)max=600T/m/s). Approach: We acquired in vivo diffusion MRI measurements with multiple diffusion times (13-30ms) up to b-values of 17.5ms/μm2 on 5 human subjects. Anisotropic Kärger model (NEXI/SMEX) was used to estimate the exchange time from the diffusion data. Results: The exchange time across the cortical ribbon is around 16ms. Impact: The high performance gradient system on the Connectome 2.0 scanner enables in vivo mapping of water exchange time in gray matter, providing a tool to study neurite permeability in the healthy human brain and a variety of neuropsychiatric disorders.