A Complete-Electrode-Model-Based Forward Approach for Transcranial Temporal Interference Stimulation with Linearization: A Numerical Simulation Study

TL;DR

This study develops and evaluates a complete electrode model-based forward simulation method for transcranial temporal interference stimulation, enabling accurate and adaptable modeling of stimulation fields considering electrode contact resistance.

Contribution

The paper introduces a comprehensive finite-element-method-based forward model for tTIS that incorporates electrode impedance and contact patch effects, and explores a linearized surrogate model for efficiency.

Findings

CEM-based simulation accurately reproduces stimulation fields.

Electrode resistance variations significantly influence field distribution.

Linearized CEM closely matches the full nonlinear model within PSNR thresholds.

Abstract

Background and Objective: Transcranial temporal interference stimulation (tTIS) is a promising non-invasive brain stimulation technique in which interference between electrical current fields extends the possibilities of electrical brain stimulation. The objective of this study is to develop an efficient mathematical tTIS forward modelling scheme that allows for realistic and adaptable simulation and can be updated accurately when the contact resistance is modified in one or more electrodes. Such a model is vital, for example, in optimization processes that seek the best possible stimulation currents to exhibit or inhibit a given brain region. This study aims to establish and evaluate the complete electrode model (CEM), i.e., a set of boundary conditions incorporating electrode impedance and contact patch, as a forward finite-element-method-based simulation technique for tTIS and investigate linearized CEM as a surrogate. Results: The CEM-based forward simulation successfully reproduced the volumetric stimulating fields induced by tTIS. Sensitivity analysis showed that variations in electrode resistance affects the field distribution, especially in regions where the interfering currents have nearly equal amplitudes. The linearized CEM model closely matched the full nonlinear model within a predefined peak signal-to-noise ratio (PSNR) threshold for relative error. Both models exhibited the highest sensitivity near the focal region.