Prospects for sub-micron solid state nuclear magnetic resonance imaging with low-temperature dynamic nuclear polarization

Abstract

We evaluate the feasibility of ¹H nuclear magnetic resonance (NMR) imaging with sub-micron voxel dimensions using a combination of low temperatures and dynamic nuclear polarization (DNP). Experiments are performed on nitroxide-doped glycerol–water at 9.4 T and temperatures below 40 K, using a 30 mW tunable microwave source for DNP. With DNP at 7 K, a 0.5 μL sample yields a ¹H NMR signal-to-noise ratio of 770 in two scans with pulsed spin-lock detection and after 80 db signal attenuation. With reasonable extrapolations, we infer that ¹H NMR signals from 1 μm³ voxel volumes should be readily detectable, and voxels as small as 0.03 μm³ may eventually be detectable. Through homonuclear decoupling with a frequency-switched Lee–Goldburg spin echo technique, we obtain 830 Hz ¹H NMR linewidths at low temperatures, implying that pulsed field gradients equal to 0.4 G/d or less would be required during spatial encoding dimensions of an imaging sequence, where d is the resolution in each dimension.