在逼真的头部几何模型中对经颅磁刺激进行线圈优化。
Coil optimisation for transcranial magnetic stimulation in realistic head geometry.
作者信息
Koponen Lari M, Nieminen Jaakko O, Mutanen Tuomas P, Stenroos Matti, Ilmoniemi Risto J
机构信息
Department of Neuroscience and Biomedical Engineering, Aalto University, P.O. Box 12200, FI-00076 AALTO, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, P.O. Box 340, FI-00029 HUS, Helsinki, Finland.
Department of Neuroscience and Biomedical Engineering, Aalto University, P.O. Box 12200, FI-00076 AALTO, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, P.O. Box 340, FI-00029 HUS, Helsinki, Finland.
出版信息
Brain Stimul. 2017 Jul-Aug;10(4):795-805. doi: 10.1016/j.brs.2017.04.001. Epub 2017 Apr 15.
BACKGROUND
Transcranial magnetic stimulation (TMS) allows focal, non-invasive stimulation of the cortex. A TMS pulse is inherently weakly coupled to the cortex; thus, magnetic stimulation requires both high current and high voltage to reach sufficient intensity. These requirements limit, for example, the maximum repetition rate and the maximum number of consecutive pulses with the same coil due to the rise of its temperature.
OBJECTIVE
To develop methods to optimise, design, and manufacture energy-efficient TMS coils in realistic head geometry with an arbitrary overall coil shape.
METHODS
We derive a semi-analytical integration scheme for computing the magnetic field energy of an arbitrary surface current distribution, compute the electric field induced by this distribution with a boundary element method, and optimise a TMS coil for focal stimulation. Additionally, we introduce a method for manufacturing such a coil by using Litz wire and a coil former machined from polyvinyl chloride.
RESULTS
We designed, manufactured, and validated an optimised TMS coil and applied it to brain stimulation. Our simulations indicate that this coil requires less than half the power of a commercial figure-of-eight coil, with a 41% reduction due to the optimised winding geometry and a partial contribution due to our thinner coil former and reduced conductor height. With the optimised coil, the resting motor threshold of abductor pollicis brevis was reached with the capacitor voltage below 600 V and peak current below 3000 A.
CONCLUSION
The described method allows designing practical TMS coils that have considerably higher efficiency than conventional figure-of-eight coils.
背景
经颅磁刺激（TMS）可对皮质进行局部、非侵入性刺激。TMS脉冲与皮质的耦合本质上较弱；因此，磁刺激需要高电流和高电压才能达到足够的强度。例如，这些要求限制了由于线圈温度升高导致的最大重复率和使用同一线圈时连续脉冲的最大数量。
目的
开发在具有任意整体线圈形状的实际头部几何结构中优化、设计和制造节能TMS线圈的方法。
方法
我们推导了一种用于计算任意表面电流分布磁场能量的半解析积分方案，用边界元法计算该分布感应的电场，并优化用于局部刺激的TMS线圈。此外，我们介绍了一种使用利兹线和由聚氯乙烯加工而成的线圈架制造这种线圈的方法。
结果
我们设计、制造并验证了一个优化的TMS线圈，并将其应用于脑刺激。我们的模拟表明，该线圈所需功率不到商用8字形线圈的一半，由于绕组几何结构优化减少了41%，由于我们使用了更薄的线圈架和降低了导体高度也有部分贡献。使用优化后的线圈，在电容电压低于600V且峰值电流低于3000A时达到了拇短展肌的静息运动阈值。
结论
所描述的方法能够设计出效率比传统8字形线圈高得多的实用TMS线圈。
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