Temporal Spherical-Harmonic Expansion and Compensation of Eddy-Current Fields Produced by Gradient Pulses

A semiautomated technique for the determination of the gradient preemphasis parameters required in NMR experiments is presented based on a temporal spherical-harmonic expansion of the magnetic fields produced following a gradient pulse. The expansion provides the strength of the harmonic which has t...

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Bibliographic Details
Published inJournal of magnetic resonance. Series A Vol. 103; no. 2; pp. 135 - 141
Main Authors Eccles, C.D., Crozier, S., Westphal, M., Doddrell, D.M.
Format Journal Article
LanguageEnglish
Published Orlando, FL Elsevier Inc 1993
Academic Press
Subjects
Atomic and molecular physics
Exact sciences and technology
Molecular properties and interactions with photons
Nuclear resonance and relaxation
Physics
Theoretical study
Spherical harmonic
NMR spectrum
Pulse sequence
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Summary:A semiautomated technique for the determination of the gradient preemphasis parameters required in NMR experiments is presented based on a temporal spherical-harmonic expansion of the magnetic fields produced following a gradient pulse. The expansion provides the strength of the harmonic which has the same symmetry as the applied gradient and additionally provides data on the more complex fields generated. Since each of these harmonics can be produced by a coil in the spectrometer shim set, the induced eddy-current fields can be nulled by applying an appropriate waveform to each shim coil. The shape of each waveform is determined by the gradient-magnet transfer function which can be calculated from the measured harmonic responses.
ISSN:1064-1858
1096-0864
DOI:10.1006/jmra.1993.1144