ANZIAM  J.  43 (2002), 375-386

NMR shim coil design utilising a rapid spherical harmonic calculation method

C. J. Snape-Jenkinson   Department of Mathematics   University of Queensland   St Lucia, QLD 4072   Australia   S. Crozier   Centre for Magnetic Resonance   University of Queensland   St Lucia, QLD 4072   Australia   and L. K. Forbes   School of Mathematics and Physics   University of Tasmania   Hobart, TAS 7001   Australia

Abstract

A rapid spherical harmonic calculation method is used for the design of Nuclear Magnetic Resonance shim coils. The aim is to design each shim such that it generates a field described purely by a single spherical harmonic. By applying simulated annealing techniques, coil arrangements are produced through the optimal positioning of current-carrying circular arc conductors of rectangular cross-section. This involves minimizing the undesirable harmonics in relation to a target harmonic. The design method is flexible enough to be applied for the production of coil arrangements that generate fields consisting significantly of either zonal or tesseral harmonics. Results are presented for several coil designs which generate tesseral harmonics of degree one.

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