Feasibility of local diffusion encoding targeting cortical surface

Motivation: Mapping of gray matter microstructure by diffusion MRI is limited by gradient strength, which sets the resolution limit toward small cells and axons. Goal(s): To use a multi-channel 3-axis TMS coil array as a miniature gradient system and generate strong local gradients. Approach: We ran simulations and ex-vivo experiments using the TMS coil as a strong local gradient for diffusion encoding. Results: The measured gradient strength matched simulated values. The TMS-gradient system was used to estimate mean diffusivity in ex-vivo tissue. Simulations show it has the potential to generate even stronger gradient fields with higher current and more coil elements. Impact: Innovations in TMS-MRI gradient design could significantly boost the achievable gradient strength for diffusion MRI in the living human brain, advancing neuroscientific research within a cost-effective design.