A hybrid passive shimming method applied to the design of a unilateral NMR magnet

Article type: Research Article

Authors: He, Wei | He, Zhonghua^*

Affiliations: School of Electrical Engineering, Chongqing University, Chongqing, China

Correspondence: [*] Corresponding author: Zhonghua He, State Key Laboratory of Power Transmission Equipment and System Security and New Technology, School of Electrical Engineering, Chongqing University, Chongqing 400030, China. Tel.: +86 13883160054; E-mail:[email protected]

Abstract: A combination of passive shimming procedures is employed in the design of a unilateral Nuclear Magnetic Resonance magnet. The first shimming procedure used movable permanent magnets to correct the inhomogeneity of the B0 field to a relatively low level. In the second shimming procedure, the small iron pieces were used as shimming units, and their sizes and locations were predicted by using an integer programming method. Finally, the distribution of the shimming pieces was optimized and a special mathematic model was established. This hybrid technique provides a computational algorithm for optimizing the B0 homogeneity and for minimizing the number of iron shimming pieces. A prototype unilateral NMR magnet has been built with this method. The B0 field measurement results were compared before and after the shimming. Employing this hybrid shimming method improved the uniformity of the B0 field from 4200 ppm to 796 ppm with only one iteration.

Keywords: Passive shimming method, integer programming, unilateral nuclear magnetic resonance (UNMR)

DOI: 10.3233/JAE-150092

Journal: International Journal of Applied Electromagnetics and Mechanics, vol. 49, no. 4, pp. 597-606, 2015