Transcranial Direct Current Stimulation Optimization - From Physics-Based Computer Simulations to High-Fidelity Head Phantom Fabrication and Measurements.

Leon Morales-Quezada,Mirret M El-Hagrassy,Felipe Fregni,R Andy Mckinley,Beatriz Costa,Pengcheng Lv

doi:10.3389/fnhum.2019.00388

Abstract

BackgroundTranscranial direct current stimulation (tDCS) modulates neural networks. Computer simulations, while used to identify how currents behave within tissues of different conductivity properties, still need to be complemented by physical models.Objective/HypothesisTo better understand tDCS effects on biology-mimicking tissues by developing and testing the feasibility of a high-fidelity 3D head phantom model that has sensing capabilities at different compartmental levels.MethodsModels obtained from MRI images generated 3D printed molds. Agar phantoms were fabricated, and 18 monitoring electrodes were placed on specific phantom brain areas.ResultsWhen using rectangular electrodes, the measured and simulated voltages at the monitoring electrodes agreed reasonably well, except at excitation locations. The electric field distribution in different phantom layers appeared better confined with circular electrodes compared to rectangular electrodes.ConclusionThe high-fidelity 3D head model was found to be feasible and comparable with computer-based electrical simulations, with high correlation between simulated and measured brain voltages. This feasibility study supports testing to further assess the reliability of this model.

Highlights

Transcranial direct current stimulation has been studied for decades and has potential therapeutic effects for a wide range of medical conditions, as well as for cognitive enhancement in healthy individuals (Andy McKinley et al, 2013)
The simulated montage using rectangular pad electrodes for bilateral dorsolateral prefrontal cortex (DLPFC) stimulation led to similar electric potential and field distributions in the gray matter and white matter (Figures 10A,B)
There was agreement between simulated and measured voltages at the skull layer’s nine monitoring electrodes (Figure 10C), except at excitation locations. Those had large discrepancies attributed to poor electric contact between the excitation electrodes and external skull surfaces

Summary

Introduction

Transcranial direct current stimulation (tDCS) has been studied for decades and has potential therapeutic effects for a wide range of medical conditions, as well as for cognitive enhancement in healthy individuals (Andy McKinley et al, 2013). With the tDCS method, weak currents (e.g., 2 mA) are injected through the scalp, which modulates neural activity in a polarity-dependent fashion at the targeted symptomor task-specific brain areas/networks to enhance function. TDCS holds great promise, it is not straightforward to determine optimum treatment procedures due to the complex shapes/configurations and the dramatic conductivity differences among various tissues, including the scalp, skull, cerebrospinal fluid (CSF), gray matter, etc. In addition to stimulating (active) electrode placement in target locations, other therapeutic treatment parameters need to be optimized, including the amplitude of the injection current, the number of injection electrodes, the surface areas of the active and reference electrodes and their configurations/montage. Transcranial direct current stimulation (tDCS) modulates neural networks. While used to identify how currents behave within tissues of different conductivity properties, still need to be complemented by physical models

Methods

Results

Conclusion