Investigation into Deep Brain Stimulation Lead Designs: A Patient-Specific Simulation Study

Abstract

New deep brain stimulation (DBS) electrode designs offer operation in voltage and current mode and capability to steer the electric field (EF). The aim of the study was to compare the EF distributions of four DBS leads at equivalent amplitudes (3 V and 3.4 mA). Finite element method (FEM) simulations (n = 38) around cylindrical contacts (leads 3389, 6148) or equivalent contact configurations (leads 6180, SureStim1) were performed using homogeneous and patient-specific (heterogeneous) brain tissue models. Steering effects of 6180 and SureStim1 were compared with symmetric stimulation fields. To make relative comparisons between simulations, an EF isolevel of 0.2 V/mm was chosen based on neuron model simulations (n = 832) applied before EF visualization and comparisons. The simulations show that the EF distribution is largely influenced by the heterogeneity of the tissue, and the operating mode. Equivalent contact configurations result in similar EF distributions. In steering configurations, larger EF volumes were achieved in current mode using equivalent amplitudes. The methodology was demonstrated in a patient-specific simulation around the zona incerta and a “virtual” ventral intermediate nucleus target. In conclusion, lead design differences are enhanced when using patient-specific tissue models and current stimulation mode.

The Physical Axon : Modeling, Simulation and Electrode Evaluation

“…The solvers were set to stop when the calculated distance difference fell below 0.01 mm. The activation distances for the 5.7 µm axon for Model I was 3.2 mm ( Figure 35), and for Model II was 2.6 mm ( Figure 34) which is in line with the distances previously published [6,10,60,67,75].…”

Adaptive Estimation of the Neural Activation Extent in Computational Volume Conductor Models of Deep Brain Stimulation

“…Field threshold values determined with this approach are used in several computational studies to estimate the neural activation extent during DBS [25], [26], [27]. The determined normalized activation thresholds determined in this study with growth factors between 29 % to 35 % for a 5.7 µm and 47 % to 74 % for a 2.0 µm axon suggest that this approach leads to an over-and underestimation of the neural activation extent with volume deviations of up to 24 % by using a constant electric field norm threshold for all stimulation amplitudes (Table II).…”

Patient-Specific Electric Field Simulations and Acceleration Measurements for Objective Analysis of Intraoperative Stimulation Tests in the Thalamus

“…There is no consensus of the degree of complexity of the model to accurately simulate the neural response, however, many groups (Chaturvedi et al, 2010; Schmidt et al, 2013; Alonso et al, 2016; Howell and McIntyre, 2016) have shown that the inclusion of the heterogeneity and anisotropy of the brain tissue increases the model accuracy and prediction capability. For instance, Chaturvedi et al (2010) and Åström et al (2012) observed an overestimation of neural activation for homogeneous models.…”

“…In a next step, it was imported into the in-house developed software (Matlab R2013) (Wårdell et al, 2012) modified for the creation of the brain tissue models. A separate filtered axial T1 image batch with enhanced region of interest was used to segment cerebrospinal fluid (CSF), gray matter and white matter (Alonso et al, 2016). The segmented image voxels were assigned with the corresponding electrical conductivities (σ) (Gabriel et al, 1996) 1 .…”

“…The Cartesian coordinates of the points describing the surface of the simulated EF volume ( Figure 3C ) were exported for further analysis. In this study an EF isolevel of 0.2 V/mm was used in order to be able to perform relative comparisons between the simulations and to comply with approximate axon diameters in the thalamus (Kuncel et al, 2008; Åström et al, 2015; Alonso et al, 2016). …”