Comparing with superconducting and permanent magnet magnetic resonance imaging (MRI) system, ultra-low- field MRI (uMRI) system has a much lower weight, which can be used in some special scenes, such as real-time image monitoring on bedside or in the ambulance for human brain disease (stroke). In order to make the uMRI system more compact, lighter, and smaller, in this work, we proposed a hybrid method for designing uMRI electromagnet. The method consists of integer linear programming (ILP) and nonlinear optimization, which were bridged by empirical principles. ILP was used to determine the coil distribution of uMRI electromagnet. Considering that the coil distribution, acquired with ILP, is not conducive for magnet processing, two empirical principles were applied to adjust the coil distribution with decreasing electromagnet performance as little as possible. At last, nonlinear optimization was exploited to eliminate the negative influence on magnetic field distribution which is introduced by coil adjustment and make electromagnet satisfy the design requirement of magnetic field homogeneity. This hybrid method combines mathematical models and empirical principles, which provides a way to design electromagnet efficiently. A small electromagnet with homogeneity of 10 ppm in a spherical region of interest (ROI) with diameter of 80 mm is designed and built in this paper.

中文翻译：

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超低场MRI的电磁铁设计

与超导和永磁磁共振成像（MRI）系统相比，超低场MRI（uMRI）系统的重量要轻得多，可用于某些特殊场合，例如床头或床旁的实时图像监控人脑疾病（中风）的救护车。为了使uMRI系统更紧凑，更轻，更小，在这项工作中，我们提出了一种设计uMRI电磁体的混合方法。该方法包括整数线性规划（ILP）和非线性优化，它们是根据经验原理进行桥接的。ILP用于确定uMRI电磁体的线圈分布。考虑到用ILP采集的线圈分布不利于磁铁加工，应用了两种经验原理来尽可能少地降低电磁性能来调整线圈分布。最后，利用非线性优化方法消除了线圈调整对磁场分布的不利影响，使电磁体满足磁场均匀性的设计要求。这种混合方法结合了数学模型和经验原理，为有效地设计电磁体提供了一种方法。本文设计并制造了一个直径为80 mm的球形感兴趣区域（ROI），其均质性为10 ppm的小型电磁体。利用非线性优化技术消除了线圈调整对磁场分布的不利影响，使电磁体满足磁场均匀性的设计要求。这种混合方法结合了数学模型和经验原理，为有效地设计电磁体提供了一种方法。本文设计并制造了一个直径为80 mm的球形感兴趣区域（ROI），其均质性为10 ppm的小型电磁体。利用非线性优化技术消除了线圈调整对磁场分布的不利影响，使电磁体满足磁场均匀性的设计要求。这种混合方法结合了数学模型和经验原理，为有效地设计电磁体提供了一种方法。本文设计并制造了一个直径为80 mm的球形感兴趣区域（ROI），其均质性为10 ppm的小型电磁体。