The shimming method used for producing high field homogeneity of the open permanent main magnet for magnetic resonance imaging (MRI) is researched in this paper. The central shimming method based on integer programming is proposed, which fulfills the combination of optimal theory and the practical manual shimming. The formulation of shimming is solved by using Lingo software and the numerical analysis method is used to compute the contribution of small shim arrays. The homogeneity of imaging region is eventually advanced nearly by 50%.The validity of the method is validated by using simulation test of shimming. The efficiency of shimming is improved through experiment corporated with the manufacturing enterprise.
1. Wilkins, J. and S. Miller, "The use of adaptive algorithms for obtaining optimal electrical shimming in magnetic resonance imaging (MRI)," IEEE Trans. on Biomedical Engineering, Vol. 36, No. 2, 202-210, 1989. doi:10.1109/10.16467
2. Yamamoto, S., et al., "Field correction of a high-homogeneous field superconducting magnet using a least squares method ," IEEE Trans. on Magnetics, Vol. 21, No. 2, 689-701, 1985. doi:10.1109/TMAG.1985.1063820
3. Belov, A. and V. Bushuev, "Passive shimming of the supercon-ducting magnet for MRI," IEEE Trans. on Applied Superconductivity, Vol. 5, No. 2, 679-681, 1995. doi:10.1109/77.402639
4. Lopez, H. S., et al., "Passive shim design and a shimming approach for biplanar permanent magnetic resonance imaging magnets," IEEE Trans. on Magnetics, Vol. 44, No. 3, 394-402, 2008. doi:10.1109/TMAG.2007.914770
5. Dorri, B. and M. E. Vermilyea, "Passive shimming of mr magnets: Algorithm, hardware, and results," IEEE Trans. on Applied Superconductivity, Vol. 3, No. 1, 254-257, 1993. doi:10.1109/77.233719
6. Wang, E., "The passive shimming technique research for a special application of the permanent magnet,", Shenyang University of Technology, Shenyang, China, 2007 (in Chinese).
7. Van de Panne, C. and F. Rahnamat, "The first algorithm for linear programming: An analysis of kantorovich's method," Ecnomics of Planning, Vol. 19, No. 2, 76-91, 1985.
8. Mitchell, J. E., "Updating lower bounds when using karmarkar's projective algorithm for linear programming," Journal of Optimization Theory and Application, Vol. 78, No. 1, 127-142, 1993. doi:10.1007/BF00940704
9. Armstrong, R. D. and P. Sinha, "Improved penalty calculations for a mixed integer branch-and-bound algorithm," Mathematical Programming, No. 6, 212-223, 1974. doi:10.1007/BF01580237
10. Ansoft Corporation, , Getting Started with Maxwell: Designing a Rotational Actuator, Maxwell v11 Magnetostatic, 2005.