从人脑轴突直径分布估计脑深部电刺激的电场影响
Estimation of electric field impact in deep brain stimulation from axon diameter distribution in the human brain
摘要：
背景资料：电场幅度（EF）的有限元法（FEM）模拟通常用于估计脑深部电刺激（DBS）电极导线主动接触周围的受影响组织。先前的研究已经发现，DBS在大约0.2 V/mm时开始显著激活轴突，对应于在单个轴突触发的模拟中激活3.4 $μ$ m轴突。然而，大脑中的大多数轴突相当小，并且随着越来越多的轴突被激活，电场的效果因此预期随着EF的增加而更强。目的：估计激活轴突的分数作为电场大小的函数。研究方法：在Medtronic 3389电极导线的FEM模拟电场中，从组合电缆和Hodgkin-Huxley模型中获得1至5 $μ$ m之间的有髓鞘轴突直径的轴突刺激所需的EF阈值。将这些阈值与来自人类大脑中几种结构的文献的平均轴突直径分布进行比较，以获得在0.1和1.8 V/mm之间的EF水平下激活的轴突分数的估计值。结果：DBS的效果估计为41 $\cdot$ EF -7.4%，从阈值水平EFt 0 = 0.18 V/mm开始。体素中DBS激活轴突的分数估计随着EF高于0.18 V/mm的阈值水平而线性增加。这意味着在为DBS绘制改善图时，EF高于0.18 V/mm与临床结果之间的线性回归是一种合适的统计方法。
英文摘要：
Background: Finite element method (FEM) simulations of the electric field magnitude (EF) are commonly used to estimate the affected tissue surrounding the active contact of deep brain stimulation (DBS) leads. Previous studies have found that DBS starts to noticeably activate axons at approximately 0.2 V/mm, corresponding to activation of 3.4 $μ$m axons in simulations of individual axon triggering. Most axons in the brain are considerably smaller however, and the effect of the electric field is thus expected to be stronger with increasing EF as more and more axons become activated. Objective: To estimate the fraction of activated axons as a function of electric field magnitude. Methods: The EF thresholds required for axon stimulation of myelinated axon diameters between 1 and 5 $μ$m were obtained from a combined cable and Hodgkin-Huxley model in a FEM-simulated electric field from a Medtronic 3389 lead. These thresholds were compared with the average axon diameter distribution from literature from several structures in the human brain to obtain an estimate of the fraction of axons activated at EF levels between 0.1 and 1.8 V/mm. Results: The effect of DBS is estimated to be 41$\cdot$EF - 7.4 % starting at a threshold level EFt0 = 0.18 V/mm. Conclusion: The fraction of activated axons from DBS in a voxel is estimated to increase linearly with EF above the threshold level of 0.18 V/mm. This means linear regression between EF above 0.18 V/mm and clinical outcome is a suitable statistical method when doing improvement maps for DBS.
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