TENEXI: Echo time-dependent neurite exchange imaging for in vivo evaluation of exchange time and relaxation time on the Connectome 2.0 scanner

Motivation: It is challenging to evaluate both T2 relaxation time and exchange time in intra-neurite and extra-cellular spaces of in vivo gray matter. Goal(s): To evaluate neurite exchange time and compartmental T2 relaxation times using a relaxation-diffusion-exchange protocol on Connectome 2.0. Approach: We acquired in vivo time-dependent diffusion-relaxation MRI data with multiple diffusion times (13-30ms) and echo times (31-120ms) using the Connectome 2.0 scanner with high-performance gradient system. Results: The exchange time and intra-neurite/extra-cellular relaxation times are about 10 ms and 120/80 ms across the cortical ribbon, respectively. Impact: In vivo mapping of water exchange and compartmental relaxation times is achievable in the brain gray matter using the high gradient performance Connectome 2.0 scanner. Multi-contrast MR protocol helps to improve the accuracy and precision in model fitting.