Micron-scale magnetic resonance imaging at very low temperatures

Authors

• HY Chen
• E Moore
• K Thurber
• R Tycko

Abstract

The spatial resolution in magnetic resonance imaging (MRI) is limited ultimately by the signal-to-noise ratio (SNR) of nuclear magnetic resonance (NMR) signals from an individual image element (i.e., one voxel). Using a microcoil for NMR excitation and detection, images with voxels as small as 40 cubic microns are detectable at room temperature, but obtaining an image with a voxel size of 1 cubic microns is essentially impossible. To overcome this barrier, we are developing MRI at very low temperatures, to take advantage of the inherent inverse dependence of NMR signal amplitudes on temperature. We have constructed a low-temperature-compatible MRI probe, including a 300 µm long microcoil with 75 micron inner diameter and a set of planar gradient coils which are all supported on sapphire plates to ensure efficient heat dissipation during gradient pulses. Frequency-switched Lee-Goldburg decoupling with an effective rotating frame field amplitude of 289 kHz has been implemented to enable high resolution imaging. A 3D image from a sample of glycerol/water mixture containing 20 micron-diameter glass spheres has been obtained at 28 K with isotropic resolution of 2.8 microns and a SNR of about 12 in two weeks. To our knowledge, this is a new world's record in MRI resolution. Experiments are now in progress to combine low-temperature MRI with dynamic nuclear polarization (DNP), a phenomenon in which NMR signals can be further enhanced by two orders of magnitude through interactions between nuclear spins and electron spins, potentially enabling sub-micron MRI. Initial results will be presented.

Scientific Focus Area: Biomedical Engineering and Biophysics

This page was last updated on Friday, March 26, 2021