Cendejas Zaragoza Leopoldo, Byrne Richard W, Rossi Marvin A
a Department of Neurological Sciences , Rush University Medical Center , Chicago , IL , USA.
b Department of Neurosurgery , Rush University Medical Center , Chicago , IL , USA.
Neurol Res. 2017 Mar;39(3):198-211. doi: 10.1080/01616412.2016.1266429. Epub 2017 Jan 12.
The objective of this work was to predict preoperatively the maximum extent to which direct stimulation therapy can propagate through an epileptic circuit for stabilizing refractory focal-onset epilepsy. A pre-surgical workflow is presented which comprises a computationally intensive process for calculating the volume of cortical activation (VOCA) surrounding cylindrical depth contacts virtually placed in white matter. The process employs an activation function (AF) derived from cable modeling of an axon. The AF was extrapolated to describe the three-dimensional activation of axon bundles facilitated by patient-specific diffusion tensor imaging (DTI).
The modeling process consisted of the following steps: (1) acquisition of structural MRI and DTI; (2) computation of the electric potential using the finite element method; (3) analysis of the effect of the modeled electric field on depolarizing axon bundles using the AF; (4) predicting distant cortical activation by strategically placing the AF seeds for creating a modulated circuit tractography (MCT) map; and finally, (5) post-implant in vivo validation using Subtracted Activated SPECT (SAS).
The pre-implant simulation calculated non-spherical volumetric regions around the contacts representing areas of hyperpolarization and depolarization. Furthermore, the generated MCT map predicted the extent to which white matter connected epileptic sources were influenced during direct stimulation therapy. Validation of this map was demonstrated post-implantation employing RNS electrocorticography and SAS. The latter technique captured transient alterations in blood flow synched to neural metabolism potentially distant to the stimulated contacts.
This pre-implant modeling system offers the potential for predicting optimal depth lead implant sites with a limited set of contacts for modulating the maximal extent of a refractory epileptogenic network.
本研究的目的是术前预测直接刺激疗法在癫痫环路中能够传播的最大范围，以稳定难治性局灶性癫痫发作。本文提出了一种术前工作流程，其中包括一个计算密集型过程，用于计算虚拟放置在白质中的圆柱形深部电极周围的皮质激活体积（VOCA）。该过程采用了从轴突电缆模型推导而来的激活函数（AF）。通过患者特异性扩散张量成像（DTI），将该AF外推以描述轴突束的三维激活。
建模过程包括以下步骤：（1）获取结构MRI和DTI；（2）使用有限元方法计算电势；（3）使用AF分析模拟电场对去极化轴突束的影响；（4）通过策略性地放置AF种子来预测远处皮质激活，以创建调制电路纤维束成像（MCT）图；最后，（5）使用减影激活单光子发射计算机断层扫描（SAS）进行植入后体内验证。
植入前模拟计算出电极周围的非球形体积区域，代表超极化和去极化区域。此外，生成的MCT图预测了在直接刺激疗法期间白质连接的癫痫源受到影响的程度。使用RNS皮层脑电图和SAS在植入后对该图进行了验证。后一种技术捕获了与受刺激电极可能距离较远的神经代谢同步的血流瞬时变化。
这种植入前建模系统有可能通过有限数量的电极预测最佳深度电极植入部位，以调节难治性致痫网络的最大范围。
