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Real‐time feedback for spatiotemporal field stabilization in MR systems
Author(s) -
Duerst Yolanda,
Wilm Bertram J.,
Dietrich Benjamin E.,
Vannesjo S. Johanna,
Barmet Christoph,
Schmid Thomas,
Brunner David O.,
Pruessmann Klaas P.
Publication year - 2015
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.25167
Subject(s) - shim (computing) , computer science , field (mathematics) , control theory (sociology) , stability (learning theory) , feedback control , control (management) , mathematics , artificial intelligence , control engineering , medicine , machine learning , erectile dysfunction , pure mathematics , engineering
Purpose MR imaging and spectroscopy require a highly stable, uniform background field. The field stability is typically limited by hardware imperfections, external perturbations, or field fluctuations of physiological origin. The purpose of the present work is to address these issues by introducing spatiotemporal field stabilization based on real‐time sensing and feedback control. Methods An array of NMR field probes is used to sense the field evolution in a whole‐body MR system concurrently with regular system operation. The field observations serve as inputs to a proportional‐integral controller that governs correction currents in gradient and higher‐order shim coils such as to keep the field stable in a volume of interest. Results The feedback system was successfully set up, currently reaching a minimum latency of 20 ms. Its utility is first demonstrated by countering thermal field drift during an EPI protocol. It is then used to address respiratory field fluctuations in a T 2 *‐weighted brain exam, resulting in substantially improved image quality. Conclusion Feedback field control is an effective means of eliminating dynamic field distortions in MR systems. Third‐order spatial control at an update time of 100 ms has proven sufficient to largely eliminate thermal and breathing effects in brain imaging at 7 Tesla. Magn Reson Med 73:884–893, 2015. © 2014 Wiley Periodicals, Inc.