Coils for large standoff relaxometry with unilateral magnets

Daniel M Gruber; Sophia N Fricke; Vanessa Lee; Bruce J Balcom; Matthew P Augustine

doi:10.1016/j.jmr.2022.107271

Coils for large standoff relaxometry with unilateral magnets

J Magn Reson. 2022 Sep:342:107271. doi: 10.1016/j.jmr.2022.107271. Epub 2022 Jul 30.

Authors

Daniel M Gruber¹, Sophia N Fricke¹, Vanessa Lee¹, Bruce J Balcom², Matthew P Augustine³

Affiliations

¹ Department of Chemistry, 69 Chemistry Building, University of California, Davis, Davis, CA 95616, USA.
² Department of Physics, UNB MRI Centre, University of New Brunswick, Fredericton, New Brunswick, Canada.
³ Department of Chemistry, 69 Chemistry Building, University of California, Davis, Davis, CA 95616, USA. Electronic address: maugust@ucdavis.edu.

PMID: 35963026
DOI: 10.1016/j.jmr.2022.107271

Abstract

Maximizing standoff distance by direct placement of probe coils on magnet bodies, while maximizing signal-to-noise is critical to the successful application of unilateral NMR. Two types of radio frequency (rf) coils for linear array, unilateral magnets are described: "simple fringe" and "split fringe coils." These coils are designed to fully exploit the standoff distance of the unilateral magnet by placement directly on the magnet surface. Such placement fails for normal surface coils used for magnetic resonance due to eddy current induced shielding by the conductive magnet surface. The coil design strategy includes a rectangular cross section solenoid coil, either continuous or split in the center, mounted with the center axis of the coil parallel to the magnet surface. These geometries, when placed on a conducting surface, enhance the rf field produced in the sample region, outside of the solenoid coil. The spatial homogeneity of both rf coils are characterized using the ANSYS™ finite element modelling software. ANSYS™ modeled coil geometries led to homogeneous, surface displaced rf fields. These coils were then constructed and characterized with magnetic resonance imaging. Finally, two experiments that use these coils to perform large standoff relaxation measurements are described.

Keywords: Portable NMR; Single-sided magnets; Unilateral magnetic resonance.