Barksdale Alex C, Ferris Natalie G, Mattingly Eli, Śliwiak Monika, Guerin Bastien, Wald Lawrence L, Davids Mathias, Klein Valerie
Massachusetts Institute of Technology.
Harvard Graduate Program in Biophysics.
Res Sq. 2024 Oct 14:rs.3.rs-4864083. doi: 10.21203/rs.3.rs-4864083/v1.
Magnetic fields switching at kilohertz frequencies induce electric fields in the body that can cause peripheral nerve stimulation (PNS). Magnetically induced PNS, i.e. magnetostimulation, has been extensively studied below 10 kHz. It is widely characterized using a hyperbolic strength-duration curve (SDC), where the PNS thresholds monotonically decrease with frequency. The very few studies performed at higher frequencies found significant deviations from the hyperbolic SDC above ~ 25 kHz, however, those measurements are sparse and show large variability. We fill the gap in the data by measuring PNS in the head of 8 volunteers using a solenoidal coil at 16 frequencies between 200 Hz and 88.1 kHz. Contrary to the hyperbolic SDC, PNS thresholds did not decrease monotonically with frequency, but reached a minimum ~ 25 kHz. The thresholds then increased by 39% from 25 kHz to 88.1 kHz on average across subjects. Our measurements can be used for guidance and validation of neurodynamic models and to inform PNS limits of magnetic resonance imaging (MRI) gradient coils and magnetic particle imaging (MPI) systems. The observed deviation of the experimentally measured thresholds from the hyperbolic SDC calls for further study of the underlying biological mechanisms of magnetostimulation beyond 25 kHz.
以千赫兹频率切换的磁场会在体内感应出电场，进而引发周围神经刺激（PNS）。磁诱导周围神经刺激，即磁刺激，已在10 kHz以下的频率范围内得到广泛研究。其通常采用双曲线强度-持续时间曲线（SDC）来表征，其中周围神经刺激阈值随频率单调下降。在较高频率下进行的研究极少，发现高于约25 kHz时与双曲线SDC存在显著偏差，然而，这些测量数据稀少且变化很大。我们通过使用螺线管线圈在200 Hz至88.1 kHz之间的16个频率下测量8名志愿者头部的周围神经刺激，填补了数据空白。与双曲线SDC相反，周围神经刺激阈值并非随频率单调下降，而是在约25 kHz时达到最小值。然后，在所有受试者中，阈值从25 kHz到88.1 kHz平均增加了39%。我们的测量结果可用于指导和验证神经动力学模型，并为磁共振成像（MRI）梯度线圈和磁粒子成像（MPI）系统的周围神经刺激限值提供参考。实验测量阈值与双曲线SDC的偏差表明，需要进一步研究25 kHz以上磁刺激的潜在生物学机制。
