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McDowell A, Conradi M. Thin high-order shims for small dipole NMR magnets. J Magn Reson. 2017;281:7-16doi: 10.1016/j.jmr.2017.04.013.
McDowell, A., & Conradi, M. (2017). Thin high-order shims for small dipole NMR magnets. Journal of magnetic resonance (San Diego, Calif. : 1997), 2817-16. https://doi.org/10.1016/j.jmr.2017.04.013
McDowell, Andrew, and Conradi, Mark. "Thin high-order shims for small dipole NMR magnets." Journal of magnetic resonance (San Diego, Calif. : 1997) vol. 281 (2017): 7-16. doi: https://doi.org/10.1016/j.jmr.2017.04.013
McDowell A, Conradi M. Thin high-order shims for small dipole NMR magnets. J Magn Reson. 2017 Aug;281:7-16. doi: 10.1016/j.jmr.2017.04.013. Epub 2017 Apr 24. PMID: 28499207.
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J Magn Reson. 2017 Aug;281:7-16. doi: 10.1016/j.jmr.2017.04.013. Epub 2017 Apr 24.

Thin high-order shims for small dipole NMR magnets.

Journal of magnetic resonance (San Diego, Calif. : 1997)

Andrew McDowell, Mark Conradi

Affiliations

  1. NuevoMR, LLC, 617 Amherst NE, Albuquerque, NM 87106, USA. Electronic address: [email protected].
  2. Washington University, Dept. of Physics, 1105, St. Louis, MO 63130, USA.

PMID: 28499207 DOI: 10.1016/j.jmr.2017.04.013

Abstract

An NMR shim coil design method that addresses the severe spatial constraints of miniaturized dipole magnets is introduced. The fundamental design element, a collection of straight wires, is shown to be sufficient for producing a complete set of shim fields of high mathematical order. In accord with these theoretical considerations, a shim set is constructed using four wires in each of four directions to create all first through fourth order fields, except one. This shim set, with its supporting structure, occupies only 2mm of the available 5mm gap in a small 1.6T magnet. However, the fields produced by the individual wires are found to differ significantly from theoretical expectations. To produce the desired harmonic shim fields, the magnetic field of each of the 32 wires is mapped in three dimensions, and linear combinations of these maps are formed. The resulting shim fields are found to be very pure. The shims are used in a prototype high-resolution NMR magnet in which the 1.0mm sample size is only possible due to the thinness of the shim set. The resulting spectra demonstrate shimming to high resolution (<25ppb FWHM) without undue heating effects.

Copyright © 2017 Elsevier Inc. All rights reserved.

Keywords: Field homogeneity; High-order shims; Matrix shims; Miniaturized NMR

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