IEEE Trans Neural Syst Rehabil Eng. 2022;30:2137-2145. doi: 10.1109/TNSRE.2022.3192761. Epub 2022 Aug 8.
Magnetic stimulation of peripheral nerves is evoked by electric field gradients caused by high-intensity, pulsed magnetic fields created from a coil. Currents required for stimulation are very high, therefore devices are large, expensive, and often too complex for many applications like rehabilitation therapy. For repetitive stimulation, coil heating due to power loss poses a further limitation. The geometry of the magnetic coil determines field depth and focality, making it the most important factor that determines the current required for neuronal excitation. However, the comparison between different coil geometries is difficult and depends on the specific application. Especially the distance between nerve and coil plays a crucial role. In this investigation, the electric field distribution of 14 different coil geometries was calculated for a typical peripheral nerve stimulation with a 27 mm distance between axon and coil. Coil parameters like field strength and focality were determined with electromagnetic field simulations. In a second analysis, the activating function along the axon was calculated, which quantifies the efficiency of neuronal stimulation. Moreover, coil designs were evaluated concerning power efficacy based on ohmic losses. Our results indicate that power efficacy of magnetic neurostimulation can be improved significantly by up to 40% with optimized coil designs.
外周神经的磁刺激是由高强度、脉冲磁场产生的电场梯度引起的，这些磁场由一个线圈产生。刺激所需的电流非常高，因此设备体积大、价格昂贵，而且对于许多应用，如康复治疗，往往过于复杂。对于重复刺激，由于功率损耗导致的线圈加热会造成进一步的限制。磁场线圈的几何形状决定了磁场的深度和聚焦性，因此它是决定神经元激发所需电流的最重要因素。然而，不同线圈几何形状之间的比较是困难的，并且取决于特定的应用。特别是神经和线圈之间的距离起着至关重要的作用。在这项研究中，为了典型的外周神经刺激，计算了 14 种不同线圈几何形状的电场分布，神经和线圈之间的距离为 27 毫米。利用电磁场模拟确定了线圈参数，如场强和聚焦性。在第二次分析中，计算了沿轴突的激活函数，它量化了神经元刺激的效率。此外，还根据欧姆损耗评估了线圈设计在功率效率方面的情况。我们的结果表明，通过优化线圈设计，磁神经刺激的功率效率可以显著提高高达 40%。
