Table_1_Steering the Volume of Tissue Activated With a Directional Deep Brain Stimulation Lead in the Globus Pallidus Pars Interna: A Modeling Study With Heterogeneous Tissue Properties.DOCX

Objective: To study the effect of directional deep brain stimulation (DBS) electrode configuration and vertical electrode spacing on the volume of tissue activated (VTA) in the globus pallidus, pars interna (GPi). Background: Directional DBS leads may allow clinicians to precisely direct current fields to different functional networks within traditionally targeted brain areas. Modeling the shape and size of the VTA for various monopolar or bipolar configurations can inform clinical programming strategies for GPi DBS. However, many computational models of VTA are limited by assuming tissue homogeneity. Methods: We generated a multimodal image-based detailed anatomical (MIDA) computational model with a directional DBS lead (1.5 mm or 0.5 mm vertical electrode spacing) placed with segmented contact 2 at the ventral posterolateral “sensorimotor” region of the GPi. The effect of tissue heterogeneity was examined by replacing the MIDA tissues with a homogeneous tissue of conductance 0.3 S/m. DBS pulses (amplitude: 1 mA, pulse width: 60 μs, frequency: 130 Hz) were used to produce VTAs. The following DBS contact configurations were tested: single-segment monopole (2B-/Case+), two-segment monopole (2A-/2B-/Case+ and 2B-/3B-/Case+), ring monopole (2A-/2B-/2C-/Case+), one-cathode three-anode bipole (2B-/3A+/3B+/3C+), three-cathode three-anode bipole (2A-/2B-/2C-/3A+/3B+/3C+). Additionally, certain vertical configurations were repeated with 2 mA current amplitude. Results: Using a heterogeneous tissue model affected both the size and shape of the VTA in GPi. Electrodes with both 0.5 mm and 1.5 mm vertical spacing (1 mA) modeling showed that the single segment monopolar VTA was entirely contained within the GPi when the active electrode is placed at the posterolateral “sensorimotor” GPi. Two segments in a same ring and ring settings, however, produced VTAs outside of the GPi border that spread into adjacent white matter pathways, e.g., optic tract and internal capsule. Both stacked monopolar settings and vertical bipolar settings allowed activation of structures dorsal to the GPi in addition to the GPi. Modeling of the stacked monopolar settings with the DBS lead with 0.5 mm vertical electrode spacing further restricted VTAs within the GPi, but the VTA volumes were smaller compared to the equivalent settings of 1.5 mm spacing.研究目标：探究定向深部脑刺激（Directional Deep Brain Stimulation, DBS）电极配置与垂直电极间距对苍白球内侧部（globus pallidus, pars interna, GPi）内激活组织体积（Volume of Tissue Activated, VTA）的影响。 研究背景：定向DBS电极可使临床医师精准地将电流场导向传统靶向脑区内的不同功能网络。针对各类单极或双极配置构建VTA的形态与大小模型，可为GPi的DBS临床编程策略提供参考依据。然而，当前多数VTA计算模型均受限于组织均质性的假设，存在一定局限性。 研究方法：本研究构建了基于多模态影像的详细解剖（Multimodal Image-based Detailed Anatomical, MIDA）计算模型，将带有分段接触电极的定向DBS电极（垂直电极间距设为1.5 mm或0.5 mm）放置于GPi的腹后外侧“感觉运动”区域，其中激活电极选用分段接触电极2。通过将MIDA组织替换为电导率为0.3 S/m的均质组织，探究组织异质性对VTA的影响。采用参数为幅值1 mA、脉冲宽度60 μs、频率130 Hz的DBS脉冲生成VTA。测试了以下DBS接触电极配置：单分段单极（2B-/Case+）、双分段单极（2A-/2B-/Case+与2B-/3B-/Case+）、环形单极（2A-/2B-/2C-/Case+）、单阴极三阳极双极（2B-/3A+/3B+/3C+）、三阴极三阳极双极（2A-/2B-/2C-/3A+/3B+/3C+）。此外，针对部分垂直电极配置，采用2 mA的电流幅值重复了建模实验。 研究结果：采用异质性组织模型会同时改变GPi内VTA的大小与形态。对垂直间距分别为0.5 mm与1.5 mm的电极（电流幅值1 mA）进行建模的结果显示，当激活电极放置于GPi的后外侧“感觉运动”区域时，单分段单极配置的VTA完全位于GPi内部。然而，同环形配置下的双分段以及环形设置所生成的VTA会超出GPi边界，并扩散至邻近的白质通路，例如视束与内囊。堆叠单极配置与垂直双极配置均可在激活GPi的同时，激活GPi背侧的相关结构。对垂直电极间距为0.5 mm的DBS电极采用堆叠单极配置建模时，VTA被进一步限制在GPi内部，但相较于电极间距为1.5 mm的等效配置，其VTA体积更小。