Tharayil Joseph J, Goetz Stefan M, Bernabei John M, Peterchev Angel V
Department of Biomedical Engineering, Duke University, Durham, NC, USA.
Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC, USA.
Neuromodulation. 2018 Jun;21(4):340-347. doi: 10.1111/ner.12699. Epub 2017 Oct 10.
The objective of this work was to characterize the magnetic field (B-field) that arises in a human brain model from the application of transcranial static magnetic field stimulation (tSMS).
The spatial distribution of the B-field magnitude and gradient of a cylindrical, 5.08 cm × 2.54 cm NdFeB magnet were simulated in air and in a human head model using the finite element method and calibrated with measurements in air. The B-field was simulated for magnet placements over prefrontal, motor, sensory, and visual cortex targets. The impact of magnetic susceptibility of head tissues on the B-field was quantified.
Peak B-field magnitude and gradient respectively ranged from 179-245 mT and from 13.3-19.0 T/m across the cortical targets. B-field magnitude, focality, and gradient decreased with magnet-cortex distance. The variation in B-field strength and gradient across the anatomical targets largely arose from the magnet-cortex distance. Head magnetic susceptibilities had negligible impact on the B-field characteristics. The half-maximum focality of the tSMS B-field ranged from 7-12 cm .
This is the first presentation and characterization of the three-dimensional (3D) spatial distribution of the B-field generated in a human brain model by tSMS. These data can provide quantitative dosing guidance for tSMS applications across various cortical targets and subjects. The finding that the B-field gradient is high near the magnet edges should be considered in studies where neural tissue is placed close to the magnet. The observation that susceptibility has negligible effects confirms assumptions in the literature.
本研究的目的是表征经颅静磁场刺激（tSMS）作用于人体脑模型时产生的磁场（B 场）。
使用有限元方法模拟了一个直径 5.08 cm、高 2.54 cm 的圆柱形钕铁硼磁体在空气中和人体头部模型中的 B 场强度和梯度的空间分布，并通过空气中的测量进行校准。模拟了磁体放置在前额叶、运动、感觉和视觉皮层靶点上时的 B 场。量化了头部组织的磁化率对 B 场的影响。
在各个皮层靶点上，B 场强度峰值和梯度分别在 179 - 245 mT 和 13.3 - 19.0 T/m 范围内。B 场强度、聚焦度和梯度随磁体与皮层距离的增加而降低。B 场强度和梯度在不同解剖靶点间的变化主要源于磁体与皮层的距离。头部磁化率对 B 场特性的影响可忽略不计。tSMS B 场的半高宽聚焦范围为 7 - 12 cm。
这是首次展示和表征 tSMS 在人体脑模型中产生的 B 场的三维（3D）空间分布。这些数据可为 tSMS 在各种皮层靶点和受试者中的应用提供定量剂量指导。在将神经组织放置在磁体附近的研究中，应考虑磁体边缘附近 B 场梯度较高这一发现。磁化率影响可忽略不计这一观察结果证实了文献中的假设。
