Salinas F S, Lancaster J L, Fox P T
Research Imaging Center, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
Phys Med Biol. 2009 Jun 21;54(12):3631-47. doi: 10.1088/0031-9155/54/12/002. Epub 2009 May 21.
Transcranial magnetic stimulation (TMS) delivers highly localized brain stimulations via non-invasive externally applied magnetic fields. This non-invasive, painless technique provides researchers and clinicians with a unique tool capable of stimulating both the central and peripheral nervous systems. However, a complete analysis of the macroscopic electric fields produced by TMS has not yet been performed. In this paper, we addressed the importance of the secondary E-field created by surface charge accumulation during TMS using the boundary element method (BEM). 3D models were developed using simple head geometries in order to test the model and compare it with measured values. The effects of tissue geometry, size and conductivity were also investigated. Finally, a realistically shaped head model was used to assess the effect of multiple surfaces on the total E-field. Secondary E-fields have the greatest impact at areas in close proximity to each tissue layer. Throughout the head, the secondary E-field magnitudes typically range from 20% to 35% of the primary E-field's magnitude. The direction of the secondary E-field was generally in opposition to the primary E-field; however, for some locations, this was not the case (i.e. going from high to low conductivity tissues). These findings show that realistically shaped head geometries are important for accurate modeling of the total E-field.
经颅磁刺激（TMS）通过外部施加的非侵入性磁场实现高度局部化的脑刺激。这种非侵入性、无痛技术为研究人员和临床医生提供了一种独特工具，能够刺激中枢和周围神经系统。然而，尚未对TMS产生的宏观电场进行完整分析。在本文中，我们使用边界元法（BEM）探讨了TMS期间表面电荷积累产生的二次电场的重要性。使用简单的头部几何形状开发了三维模型，以测试模型并将其与测量值进行比较。还研究了组织几何形状、大小和电导率的影响。最后，使用逼真形状的头部模型评估多个表面对总电场的影响。二次电场在每个组织层附近的区域影响最大。在整个头部，二次电场强度通常为一次电场强度的20%至35%。二次电场的方向通常与一次电场相反；然而，在某些位置并非如此（即从高电导率组织到低电导率组织）。这些发现表明，逼真形状的头部几何形状对于准确模拟总电场很重要。
