Chen Haoran, Wang Yaohui, Wang Wenchen, Zhou Guyue, Wu Pengfei, Qu Hongyi, Liu Jianhua, Li Liang, Liu Feng
Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China; School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, People's Republic of China; School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
J Magn Reson. 2024 Jul;364:107711. doi: 10.1016/j.jmr.2024.107711. Epub 2024 Jun 10.
In the design of ultrahigh field nuclear magnetic resonance (NMR) superconducting magnets, it typically requires a high homogeneous magnetic field in the diameter of spherical volume (DSV) to obtain high spectrum resolution. However, shimming technique presents challenges due to the magnet bore space limitations, as accurate measurement of magnetic field distribution is very difficult, especially for customized micro-bore magnets. In this study, we introduced an active shimming method that utilized iterative adjustment of shim coil currents to improve the magnetic field homogeneity based on the full width at half maximum (FWHM) of the spectrum. The proposed method can determine the optimal set of currents for shim coils, effectively enhancing spatial field homogeneity by converging the FWHM. Experimental validation on a 25 T NMR superconducting magnet demonstrated the efficacy of the proposed method. Specifically, the active shimming method improved the field homogeneity of a 10 mm DSV from 7.09 ppm to 2.27 ppm with only four shim coils, providing a superior magnetic field environment for solid NMR and further magnetic resonance imaging (MRI) experiment. Furthermore, the proposed method can be promoted to more customized micro-bore magnets that require high magnetic field homogeneity.
在超高场核磁共振（NMR）超导磁体的设计中，通常需要在球形体积直径（DSV）内获得高均匀度的磁场，以实现高光谱分辨率。然而，由于磁体孔空间的限制，匀场技术面临挑战，因为磁场分布的精确测量非常困难，特别是对于定制的微孔磁体。在本研究中，我们引入了一种主动匀场方法，该方法基于光谱的半高宽（FWHM），通过迭代调整匀场线圈电流来提高磁场均匀度。所提出的方法可以确定匀场线圈的最佳电流组合，通过收敛FWHM有效地增强空间场均匀度。在一台25 T NMR超导磁体上进行的实验验证了该方法的有效性。具体而言，主动匀场方法仅使用四个匀场线圈就将10 mm DSV的场均匀度从7.09 ppm提高到了2.27 ppm，为固体NMR和进一步的磁共振成像（MRI）实验提供了优越的磁场环境。此外，所提出的方法可以推广到更多需要高磁场均匀度的定制微孔磁体上。
