Advancing Ultra-High Field Magnetic Resonance Microscopy

Abstract

Magnetic resonance microscopy (MRM) is capable of probing fine structures and complex functions of living tissue. MRM suffers from decreased SNR and long scan times approaching 10s of hours to achieve sub 10 µm isotropic voxel sizes. Furthermore, as voxels shrink in size, attenuation from diffusion of spins becomes more apparent. Acquisitions well-suited for human imaging at relatively low resolution suffer decreased SNR and considerable resolution broadening for µm resolution imaging. Careful experimental demonstration of diffusion’s effects of line broadening and signal attenuation at resolutions below 10 µm will quantify the exact conditions frequency encoding under performs phase encoding. To further improve SNR and decrease scan times, hardware noise is minimized via cryogenically cooled electronics. Selective cooling of necessary circuitry within a cryogenic chamber results in imaging SNR improvements by a factor of 2. The novel design allows the inductive element of the circuit to remain in ambient air. With optimized acquisitions, excised rat spinal cord is imaged with 10 µm in-plane resolution resolving nerve roots in the white matter and vessels in the gray matter. Excised murine kidneys are imaged with 94 x 92 x 92 µm resolution revealing changes in R1rho of fibrosis in the outer stripe of the outer medulla.