Microstructural Heterogeneity of Tissues Revealed by High-Resolution MR Microscopy at 15.2 T

Motivation: To identify the spatial limit of fast exchange on proton relaxation in excised tissues by measuring how relaxation rate depends on water content at different resolutions. Goal(s): To map T1 and M0 variations within a section across resolutions using MR microscopy. Approach: We employed a micro-coil, high magnetic field, strong gradients, and a fast pulse sequence method to map T1 and M0 at very high spatial resolution. Results: High-resolution maps revealed significant heterogeneity of R1 (=1/T1) and M0 beyond noise. The slope of R1 v. M0 also varied across resolutions, possibly indicating the breakdown of the fast exchange of spins within larger voxels. Impact: The study offers insight into T1 relaxation and spin exchange dynamics at the microscopic level.