Comparison of preemphasis based on a broadband filter vs. a standard exponential model for higher-order dynamic shimming
Signe Johanna Vannesjo1, Yuhang Shi1, Klaas P Pruessmann2, Andrew Dewdney3, Karla L Miller1, and Stuart Clare1
1FMRIB centre, NDCN, University of Oxford, Oxford, United Kingdom, 2Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland, 3Magnetic Resonance, Siemens Healthcare GmbH, Erlangen, Germany
Traditionally, shim preemphasis filters to compensate for
eddy current fields have consisted of a sum of exponentially decaying terms. It
has recently been proposed to instead implement a non-parametric preemphasis
filter based on the shim impulse response function. This can address features
that are not captured with the exponential model, such as oscillatory responses.
We here compared the two preemphasis approaches for higher-order dynamic shim
updating. The non-parametric filter yielded an improved frequency response of
the system and about 10 ms faster shim settling, as well as suppression of field
oscillations after a shim step.
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