Multi-Compartment Volume Conductor with Complete Electrode Model: Simulated Stereo-EEG Source Localization using Brainstorm-Zeffiro Plugin

TL;DR

Accurate localization of brain activity from combined scalp-EEG and stereo-EEG requires realistic, multi-compartment head models with accurate electrode modeling. The BST-ZI pipeline transfers BST segmentations and atlases into Zeffiro for FE mesh generation and forward/inverse modeling with a complete electrode model, enabling end-to-end MRI-to-lead-field computations. It constructs a 116-compartment head model from BST using Desikan-Killiany and Aseg atlases, includes 72 scalp electrodes and a 4-contact stereo-EEG probe, and employs a base mesh around 0.6 mm refined to ~0.3 mm near the probe to enable accurate forward solutions. Findings show that including stereo-EEG data concentrates the lead field near the implant and improves thalamic source localization, with better reconstructions when the dipole orientation is near parallel to the probe; the BST-ZI workflow supports integrated, DBS-oriented source localization that can inform planning.

Abstract

This study introduces a novel integration of the Brainstorm (BST) software and the Zeffiro Interface (ZI) to enable whole-head, multi-compartment volume conductor modeling for electroencephalography (EEG) source imaging, with a particular focus on stereotactic EEG applications. We present the BST-2-ZI plugin, a MATLAB-based tool that facilitates seamless transfer of tissue segmentations and anatomical atlases from BST into ZI for finite element (FE) mesh generation as well as forward and inverse modeling. The generated FE meshes support variable spatial resolution and implement the complete electrode model (CEM), allowing for precise modeling of both invasive depth electrodes and non-invasive scalp electrodes. Using the ICBM152 template and synthetic source simulation, we demonstrate the end-to-end pipeline from MRI data to lead field (LF) computation and source localization in a stereotactic EEG (stereo-EEG) setting. Our numerical experiments highlight the capability of the pipeline to accurately model multi-compartment head geometry and conductivity with a stereotactic CEM-based electrode configuration. Our preliminary source localization results show how a synthetic stereo-EEG probe corresponding to a bidirectional deep brain stimulation (DBS) probe with four omnidirectional contacts can, in principle, be coupled with scalp electrodes to improve source localization in its vicinity.

Figures (6)

• Figure 1: BST-2-ZI plugin dialog window as it appears when called from BST in a MATLAB environment. This interface allows the user to select the required input files for mesh generation—namely, the settings file and the run script—and to define the run mode (Fresh start, Import compartments, or Use project).
• Figure 2: A transparent surface segmentation of the whole head (left) with the stereo-EEG probe and the compartments inside the CSF layer (right) as of after importing them from BST to ZI. Altogether, the number of compartments (scouts) imported from tissue atlas, Desikan-Killiany atlas and Aseg atlas, was 116. The electrical conductivities (S/m) of the different tissue types represented by those were chosen to be isotropic with the following values: white matter 0.14, gray matter 0.33, CSF 1.79, scalp 0.43, eyes 1.5, compact bone 0.0064, spongy bone 0.028, blood 0.7, muscle 0.33, probe 1E-15, and probe encapsulation 0.33. The white and gray matter compartments were composed of various sub-compartments of the Desikan-Killiany and Aseg atlas.
• Figure 3: A tetrahedral FE mesh with overall 0.6 mm resolution was generated as described in galaz2023multi based on the 116 imported compartments together with 72 scalp electrodes, placed according to 10-20 system and a cylindrical stereo-EEG probe model with its 4 omnidirectional contacts (approximating those of Medtronic 3389, see, e.g., anderson2018optimized) reaching the ANT region.
• Figure 4: Deep structures with stereo-EEG probe; the FE mesh was refined in the vicinity of the probe to result in accuracy of approximately 0.3 mm with respect to the surface model. From Top to bottom: Ventricle Lateral (Dark purple), Putamen (Magenta), Hippocampus (Yellow), Amygdala (Cyan), Ventral Diencephalon (Red), Thalamus (Green).
• Figure 5: The relative stereo LF amplitude for stereo-EEG and scalp-EEG as a volumetric distribution in decibels with respect to minimum value 0 dB and with 10 dB as a top threshold value. In the case of stereo-EEG the field can be observed to be concentrated into the vicinity of the probe, while for scalp-EEG, the amplitudes are observed to be more evenly distributed with a growth towards the scalp electrodes.