脑深部电刺激期间电极阻抗的来源及影响
Sources and effects of electrode impedance during deep brain stimulation.
作者信息
Butson Christopher R, Maks Christopher B, McIntyre Cameron C
机构信息
Department of Biomedical Engineering, Cleveland Clinic Foundation, 9500 Euclid Ave. ND-20, Cleveland, OH 44195, USA.
出版信息
Clin Neurophysiol. 2006 Feb;117(2):447-54. doi: 10.1016/j.clinph.2005.10.007. Epub 2005 Dec 22.
OBJECTIVE
Clinical impedance measurements for deep brain stimulation (DBS) electrodes in human patients are normally in the range 500-1500 Omega. DBS devices utilize voltage-controlled stimulation; therefore, the current delivered to the tissue is inversely proportional to the impedance. The goals of this study were to evaluate the effects of various electrical properties of the tissue medium and electrode-tissue interface on the impedance and to determine the impact of clinically relevant impedance variability on the volume of tissue activated (VTA) during DBS.
METHODS
Axisymmetric finite-element models (FEM) of the DBS system were constructed with explicit representation of encapsulation layers around the electrode and implanted pulse generator. Impedance was calculated by dividing the stimulation voltage by the integrated current density along the active electrode contact. The models utilized a Fourier FEM solver that accounted for the capacitive components of the electrode-tissue interface during voltage-controlled stimulation. The resulting time- and space-dependent voltage waveforms generated in the tissue medium were superimposed onto cable model axons to calculate the VTA.
RESULTS
The primary determinants of electrode impedance were the thickness and conductivity of the encapsulation layer around the electrode contact and the conductivity of the bulk tissue medium. The difference in the VTA between our low (790 Omega) and high (1244 Omega) impedance models with typical DBS settings (-3 V, 90 mus, 130 Hz pulse train) was 121 mm3, representing a 52% volume reduction.
CONCLUSIONS
Electrode impedance has a substantial effect on the VTA and accurate representation of electrode impedance should be an explicit component of computational models of voltage-controlled DBS.
SIGNIFICANCE
Impedance is often used to identify broken leads (for values > 2000 Omega) or short circuits in the hardware (for values < 50 Omega); however, clinical impedance values also represent an important parameter in defining the spread of stimulation during DBS.
目的
人类患者深部脑刺激（DBS）电极的临床阻抗测量通常在500 - 1500欧姆范围内。DBS设备采用电压控制刺激；因此，传递到组织的电流与阻抗成反比。本研究的目的是评估组织介质和电极 - 组织界面的各种电学性质对阻抗的影响，并确定临床相关阻抗变异性对DBS期间组织激活体积（VTA）的影响。
方法
构建DBS系统的轴对称有限元模型（FEM），明确表示电极和植入式脉冲发生器周围的封装层。通过将刺激电压除以沿有源电极触点的积分电流密度来计算阻抗。模型使用傅里叶有限元求解器，该求解器在电压控制刺激期间考虑了电极 - 组织界面的电容成分。将在组织介质中生成的随时间和空间变化的电压波形叠加到电缆模型轴突上，以计算VTA。
结果
电极阻抗的主要决定因素是电极触点周围封装层的厚度和电导率以及大块组织介质的电导率。在典型DBS设置（-3 V，90 μs，130 Hz脉冲串）下，我们的低阻抗（790欧姆）和高阻抗（1244欧姆）模型之间的VTA差异为121 mm³，体积减少了52%。
结论
电极阻抗对VTA有显著影响，并准确表示电极阻抗应该是电压控制DBS计算模型的一个明确组成部分。
意义
阻抗通常用于识别硬件中的断连导线（对于值> 2000欧姆）或短路（对于值< 50欧姆）；然而，临床阻抗值也是定义DBS期间刺激扩散范围中的一个重要参数。
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