Evaluating passively shielded gradient coil configurations for optimal eddy current compensation

Sanchez Lopez, Hector, Poole, Michael and Crozier, Stuart (2010) Evaluating passively shielded gradient coil configurations for optimal eddy current compensation. Journal of Physics D - Applied Physics, 43 19: 1-13. doi:10.1088/0022-3727/43/19/195005

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Author Sanchez Lopez, Hector
Poole, Michael
Crozier, Stuart
Title Evaluating passively shielded gradient coil configurations for optimal eddy current compensation
Journal name Journal of Physics D - Applied Physics   Check publisher's open access policy
ISSN 0022-3727
Publication date 2010-05-19
Sub-type Article (original research)
DOI 10.1088/0022-3727/43/19/195005
Volume 43
Issue 19
Start page 1
End page 13
Total pages 13
Place of publication Bristol, England
Publisher Institute of Physics Publishing Ltd.
Collection year 2011
Language eng
Abstract In magnetic resonance imaging, rapidly switching magnetic fields are used to spatially encode the signal. The temporal change of these fields induces eddy currents in nearby conducting structures of the scanner. These eddy currents, in turn, generate a secondary magnetic field that opposes and distorts the desired gradient field. Eddy current compensation methods are generally applied assuming that the primary and secondary magnetic field gradients possess similar spatial characteristics in the imaging volume (field matching). In this work an optimization method is used to deform the shape of the coil support and/or a highly conductive passive shield in order to improve the field matching and reduce the inductive coupling between the gradient coil and the passive shield. Using the residual field after eddy current compensation as the objective function, the coil support and/or conducting surfaces were deformed to obtain passively shielded x- and z-gradient coils with improved field matching and eddy current compensation. Assuming a single frequency, quasi-static simulation, it was demonstrated that the residual field was reduced up to 24 times by reshaping the coil and passive shield surfaces due to the improved field matching. However, using transient analyses we showed that in the case of the passively shielded x-gradient coil the residual field may only be reduced by five times from a cylindrical coil configuration. A bulge shape is created in the conducting surface as a mechanism of matching the field and at the same time reducing the mutual inductive coupling between the coil and the passive shield. An actively shielded coil with control over the magnetic field produced by the induced current was used as a reference coil that produces the minimal residual field. The actively shielded gradient coil produces minimal residual field for short and long pulses in the transient analyses. © 2010 IOP Publishing Ltd.
Keyword Magnetic-field Gradients
Superconducting magnets
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Published 28 April 2010. Article number 195005

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2011 Collection
School of Information Technology and Electrical Engineering Publications
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Citation counts: TR Web of Science Citation Count  Cited 1 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 5 times in Scopus Article | Citations
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Created: Sun, 16 May 2010, 00:03:27 EST