Wei Xile, Li Yao, Lu Meili, Wang Jiang, Yi Guosheng
Tianjin Key Laboratory of Process Measurement and Control, School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China.
School of Information Technology Engineering, Tianjin University of Technology and Education, Tianjin 300222, China.
Int J Environ Res Public Health. 2017 Nov 14;14(11):1388. doi: 10.3390/ijerph14111388.
Multi-coil arrays applied in transcranial magnetic stimulation (TMS) are proposed to accurately stimulate brain tissues and modulate neural activities by an induced electric field (EF). Composed of numerous independently driven coils, a multi-coil array has alternative energizing strategies to evoke EFs targeting at different cerebral regions. To improve the locating resolution and the stimulating focality, we need to fully understand the variation properties of induced EFs and the quantitative control method of the spatial arrangement of activating coils, both of which unfortunately are still unclear. In this paper, a comprehensive analysis of EF properties was performed based on multi-coil arrays. Four types of planar multi-coil arrays were used to study the relationship between the spatial distribution of EFs and the structure of stimuli coils. By changing coil-driven strategies in a basic 16-coil array, we find that an EF induced by compactly distributed coils decays faster than that induced by dispersedly distributed coils, but the former has an advantage over the latter in terms of the activated brain volume. Simulation results also indicate that the attenuation rate of an EF induced by the 36-coil dense array is 3 times and 1.5 times greater than those induced by the 9-coil array and the 16-coil array, respectively. The EF evoked by the 36-coil dispense array has the slowest decay rate. This result demonstrates that larger multi-coil arrays, compared to smaller ones, activate deeper brain tissues at the expense of decreased focality. A further study on activating a specific field of a prescribed shape and size was conducted based on EF variation. Accurate target location was achieved with a 64-coil array 18 mm in diameter. A comparison between the figure-8 coil, the planar array, and the cap-formed array was made and demonstrates an improvement of multi-coil configurations in the penetration depth and the focality. These findings suggest that there is a tradeoff between attenuation rate and focality in the application of multi-coil arrays. Coil-energizing strategies and array dimensions should be based on an adequate evaluation of these two important demands and the topological structure of target tissues.
应用于经颅磁刺激（TMS）的多线圈阵列旨在通过感应电场（EF）精确刺激脑组织并调节神经活动。多线圈阵列由众多独立驱动的线圈组成，具有多种交替通电策略，可诱发针对不同脑区的电场。为了提高定位分辨率和刺激聚焦性，我们需要充分了解感应电场的变化特性以及激活线圈空间排列的定量控制方法，然而不幸的是，这两者目前仍不清楚。本文基于多线圈阵列对电场特性进行了全面分析。使用了四种类型的平面多线圈阵列来研究电场的空间分布与刺激线圈结构之间的关系。通过在基本的16线圈阵列中改变线圈驱动策略，我们发现紧密分布的线圈所感应的电场比分散分布的线圈所感应的电场衰减更快，但前者在激活脑体积方面比后者具有优势。模拟结果还表明，36线圈密集阵列所感应的电场衰减率分别比9线圈阵列和16线圈阵列所感应的电场衰减率大3倍和1.5倍。36线圈分散阵列所诱发的电场衰减率最慢。这一结果表明，与较小的多线圈阵列相比，较大的多线圈阵列以降低聚焦性为代价激活更深的脑组织。基于电场变化对激活特定形状和大小的场进行了进一步研究。使用直径为18毫米的64线圈阵列实现了精确的目标定位。对8字形线圈、平面阵列和帽状阵列进行了比较，结果表明多线圈配置在穿透深度和聚焦性方面有所改进。这些发现表明，在多线圈阵列的应用中，衰减率和聚焦性之间存在权衡。线圈通电策略和阵列尺寸应基于对这两个重要要求以及目标组织拓扑结构的充分评估。
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