Comparing Isotropic and Anisotropic Brain Conductivity Modeling: Planning Optimal Depth-Electrode Placement in White Matter for Direct Stimulation Therapy in an Epileptic Circuit

A novel depth electrode placement planning strategy is presented for calculating a patient-specific brain conductivity map for predicting the extent to which direct stimulation therapy can strategically propagate through pathological white matter. Our laboratory developed isotropic and anisotropic human brain finite element method (FEM) models derived from magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI), respectively, for estimating tissue conductivities during direct stimulation therapy. Specifically, the electrostatic electric field (E-field) and, current density surrounding two modeled depth contacts virtually placed in white matter were modeled for a patient with bilaterally independent intractable temporal lobe epileptic sources. The more sophisticated anisotropic model was developed to challenge our three-compartment isotropic model (Rossi et al, 2010). The isotropic model was used to plan optimal implantation of a 4-contact depth lead connected to an investigational implantable pulse generator (NeuroPace®, Inc) recently recommended for approval by the U.S. Food and Drug Administration.