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第14届中国系统仿真技术及其应用学术年会

作者： Haicheng WU 1,2,Li JING 3,Shiyou YANG 1 1 College of electrical engineering,Zhejiang University,Hangzhou,China 2 Anhui electric power research institute,Hefei,China 3 Ningbo Xingaoyi Magnetic Material Company,Yuyao,China

The impurities of various harmonic orders in region of MRI magnetic field will depress the qualities of the *** on the direct proportional relationship of FID signal of MRI system and magnetic field homogeneity,an efficient optimization algorithm of active shimming is presented to correct the inhomogeneous *** intensity is used as feedback information to calculate the shim currents with adaptive *** makes the calculation process independent of the coils hardware parameters and the correction function of the coils be put forth *** experiment results show that the optimal shim currents can be quickly worked out in less than 3 *** field homogeneity and qualities of the image are evidently improved by the novel method.

关键词： active shimming shim coils shim currents homogeneity FID

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A novel approach to designing cylindrical-surface shim coils for a superconducting magnet of magnetic resonance imaging

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Chinese Physics B 2010年第1期19卷 563-574页

作者：刘文韬俎栋林唐昕 Beijing Key Laboratory of Medical Physics and Engineering IHIP of Physics SchoolPeking University

For a superconducting magnet of magnetic resonance imaging （MRI）, the novel approach presented in this paper allows the design of cylindrical gradient and shim coils of finite length. The method is based on identification of the weighting of harmonic components in the current distribution that will generate a magnetic field whose z-component follows a chosen spherical harmonic function. Mathematical expressions which relate the harmonic terms in the cylin- drical current distribution to spherical harmonic terms in the field expansion are established. Thus a simple matrix inversion approach can be used to design a shim coil of any order pure harmonic. The expressions providing a spherical harmonic decomposition of the field components produced by a particular cylindrical current distribution are novel. A stream function was applied to obtain the discrete wire distribution on the cylindrical-surface. This method does not require the setting of the target-field points. The discussion referring to matrix equations in terms of condition numbers proves that this novel approach has no ill-conditioned problems. The results also indicate that it can be used to design cylindrical-surface shim coils of finite length that will generate a field variation which follows a particular spherical harmonic over a reasonably large-sized volume.

关键词： active shimming superconducting MRI magnet target-field approach harmonic coils

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active shim coils design for Halbach magnet based on inverse boundary element method

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Magnetic Resonance Letters 2022年第3期2卷 159-169页

作者： Yajie Xu Feng Wang Ya Wang Peng Yu Jingzhong Zhang Xiaodong Yang Suzhou Institute of Biomedical Engineering and Technology Chinese Academy of SciencesSuzhou215163China School of Electronics and Information Engineering Changchun University of Science and TechnologyChangchun130022China School of Biomedical Engineering(Suzhou) Division of Life Sciences and MedicineUniversity of Science and Technology of ChinaHefei230026China Jinan Guoke Medical Technology Development Co. LtdJinan250101China

With advantages of small volume,high field strength,and compact stray field,the Halbach array magnet is of great potential in desktop NMR ***,field inhomogeneity poses a main obstacle to its *** shimming is necessary for improving the field *** active shim coil design method for cylindrical Halbach magnet based on inverse boundary element method(iBEM)is introduced in this *** coils targeting 1st~3rd and Z4/Z5/Z6 spherical harmonic(SH)terms were designed with constraints of field accuracy,resistance,inductance,and current *** loops and symmetric property influence were discussed to further improve the performance of high-order shim ***,with the prototype of the shim coils constructed,field pattern and SH transformation proved that the coils designed could fit the target SH distribution,though contamination from low-order components existed in highorder terms.A practical shimming experiment on the Halbach magnet has improved the homogeneity from 40.3 ppm to 3.8 ppm in radius 2.5 mm,height 5 mm cylindrical sample space,verifying the coils'compensation *** work provides a flexible inverse coil design method for cylindrical Halbach magnet and discusses the high-order shim coil design and implementation,which is potential in nuclear magnetic resonance applications based on Halbach magnet arrays.

关键词： active shimming iBEM Halbach Magnetic resonance

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