A hybrid field-harmonics approach for passive shimming design in MRI

Liu, Feng, Zhu, Jianfeng, Xia, Ling and Crozier, Stuart (2011) A hybrid field-harmonics approach for passive shimming design in MRI. IEEE Transactions on Applied Superconductivity, 21 2: 60-67. doi:10.1109/TASC.2011.2112358


Author Liu, Feng
Zhu, Jianfeng
Xia, Ling
Crozier, Stuart
Title A hybrid field-harmonics approach for passive shimming design in MRI
Journal name IEEE Transactions on Applied Superconductivity   Check publisher's open access policy
ISSN 1051-8223
1558-2515
Publication date 2011-04
Sub-type Article (original research)
DOI 10.1109/TASC.2011.2112358
Volume 21
Issue 2
Start page 60
End page 67
Total pages 9
Place of publication Piscataway, NJ, U.S.A.
Publisher IEEE
Collection year 2012
Language eng
Formatted abstract This paper presents a new passive shimming (PS) design scheme for the correction of static magnetic-field inhomogeneities in magnetic resonance imaging (MRI) systems. In MRI, the PS procedure usually employs magnetic-field-based or harmonic-based methods to find an optimal iron-piece configuration to improve the uniformity of the static magnetic field in the imaging region. For the field-based PS technique, the peak-to-peak field inhomogeneity is minimized, and the harmonic components are inherently unconstrained; in the harmonic-based scheme, selected unwanted harmonics are minimized, and the overall field uniformity is consequently reduced. The field approach usually provides good field homogeneity but lacks flexibility in managing all terms of spherical harmonic field expansion; the harmonic approach is capable of controlling targeted low-order harmonic terms but can have difficulty in producing optimal overall field homogeneity and in controlling high-order harmonics. The new algorithm proposed herein attempts to combine the strengths of these two methods for a better PS solution. During the PS implementation, an explicit expression of the system matrix with both the field and harmonic sensitivities is generated, and then, an optimization procedure is performed for the determination of shim-piece thicknesses and locations. A case study presented shows that the hybrid method provides good quality, flexible solutions for controlling individual harmonic impurities, and also overall field uniformity. This method is not only applicable to conventional MRI magnets, but also, its flexibility means that it can be easily used to shim unconventional electromagnets.
Keyword Hybrid approach
Magnetic field
Magnetic resonance imaging (MRI)
Optimization
Passive shimming (PS)
Zonal and tesseral harmonics
Magnet
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2012 Collection
School of Information Technology and Electrical Engineering Publications
 
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Created: Tue, 20 Dec 2011, 13:03:51 EST by Ms Deborah Brian on behalf of School of Information Technol and Elec Engineering