Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC 27710, United States of America.
J Neural Eng. 2018 Aug;15(4):046033. doi: 10.1088/1741-2552/aac967. Epub 2018 Jun 1.
Transcranial magnetic stimulation (TMS) is a noninvasive brain stimulation technique used for research and clinical applications. Existent TMS coils are limited in their precision of spatial targeting (focality), especially for deeper targets. This paper presents a methodology for designing TMS coils to achieve optimal trade-off between the depth and focality of the induced electric field (E-field), as well as the energy required by the coil.
A multi-objective optimization technique is used for computationally designing TMS coils that achieve optimal trade-offs between E-field focality, depth, and energy (fdTMS coils). The fdTMS coil winding(s) maximize focality (minimize the volume of the brain region with E-field above a given threshold) while reaching a target at a specified depth and not exceeding predefined peak E-field strength and required coil energy. Spherical and MRI-derived head models are used to compute the fundamental depth-focality trade-off as well as focality-energy trade-offs for specific target depths.
Across stimulation target depths of 1.0-3.4 cm from the brain surface, the suprathreshold volume can be theoretically decreased by 42%-55% compared to existing TMS coil designs. The suprathreshold volume of a figure-8 coil can be decreased by 36%, 44%, or 46%, for matched, doubled, or quadrupled energy. For matched focality and energy, the depth of a figure-8 coil can be increased by 22%.
Computational design of TMS coils could enable more selective targeting of the induced E-field. The presented results appear to be the first significant advancement in the depth-focality trade-off of TMS coils since the introduction of the figure-8 coil three decades ago, and likely represent the fundamental physical limit.
经颅磁刺激（TMS）是一种用于研究和临床应用的非侵入性脑刺激技术。现有的 TMS 线圈在空间靶向（聚焦性）的精度上存在局限性，尤其是对于较深的目标。本文提出了一种设计 TMS 线圈的方法，以在诱导电场（E 场）的深度和聚焦性以及线圈所需的能量之间实现最佳折衷。
使用多目标优化技术对 TMS 线圈进行计算机设计，以在 E 场聚焦性、深度和能量之间实现最佳折衷（fdTMS 线圈）。fdTMS 线圈绕组（多个）最大化聚焦性（使电场超过给定阈值的脑区体积最小化），同时达到指定深度的目标，并且不超过预设的峰值 E 场强度和所需的线圈能量。使用球形和 MRI 衍生的头部模型来计算基本的深度聚焦性折衷以及特定目标深度的聚焦性能量折衷。
在距大脑表面 1.0-3.4 cm 的刺激目标深度范围内，与现有的 TMS 线圈设计相比，超阈值体积理论上可减少 42%-55%。对于匹配、加倍或四倍能量的环形线圈，超阈值体积可分别减少 36%、44%或 46%。对于匹配的聚焦性和能量，环形线圈的深度可增加 22%。
TMS 线圈的计算设计可以实现对诱导 E 场的更具选择性的靶向。所呈现的结果似乎是自三十年前引入环形线圈以来 TMS 线圈在深度聚焦性折衷方面的首次重大进展，并且可能代表了基本的物理极限。
