14T MRI大口径全身自屏蔽超导磁体的一种优化设计方法

磁共振成像(MRI)的磁体设计首先是确保中心成像区的场值和均匀性, 二是尽可能减少场值耗散的距离即漏磁5Gs 线. 基于此本文提出了一种线性与非线性规划联合优化的方法. 首先将导体作为基本单元, 在预布置线圈的空间范围内构建二维连续导体网格. 通过线性规划搜索满足磁场约束条件的网格电流分布图. 再将存在电流的网格离散为一个个矩形线圈区域, 在保证场值均匀性、 杂散场5 Gs 线范围以及线圈位置间隔、 导体超导线安全裕度的前提下利用非线性规划, 具体确定各个线圈的轴向和径向位置、 线圈内导体层数和各层匝数以及通电流大小等. 采用这种联合优化方法, 不仅节省优化时间, 还可以自行设计线圈形状有利于工程实现. 文中由此方法给出了14 T MRI 磁体的一种设计方案, 依靠4 组线圈使得45 cm 中心球形成像内不均匀度降低到5 ppm, 而高场耗散的5 Gs 线通过磁体自屏蔽减小到15 m 以内. 满足了设计的要求.

An Optimal Design Method for14 T MRI Full-body Self-shielding Super conducting Magnets

Magnetic design of magnetic resonance imaging (MRI) is firstly to ensure the field value and uniformity of the central imaging area, and secondly to minimize the field value dissipation distance, namely magneticleakage5 Gs line. Based on this, a joint optimization method of linear and nonlinear programming is proposed. Firstly, the conductor is used as the basic unit to construct a two-dimensional continuous conductor grid within the space range of the prearranged coil. The grid current distribution diagram satisfying the constraint condition of magnetic field is searched by linear programming. Then discrete grid with current will be adjusted to a rectangular coil area, in guarantee the uniformity of the field value, scope of stray field line 5 Gs and coil position interval, the superconducting wire safety margin by using nonlinear programming, specific each coil structure and position parameters. By using this joint optimization method, not only the optimization time can be saved, but also the coil shape can be designed by special need, which is beneficial to engineering realization.In this paper, a design scheme of14 T MRI magnet is presented, which reduces the inhomogeneity in the spherical image at the center of 45 cm to 5 ppm by 4 coils, while the high-field dissipation line of 5 Gs decreases to less than 15 m through the magnetic self-shielding effect. Finally It meets the design requirements.