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

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.

EEG modulation by different transcranial direct current stimulation (tDCS) montages: a randomized double-blind sham-control mechanistic pilot trial in healthy participants

“…When using the bilateral dorsolateral prefrontal cortex (DLPFC) tDCS montage, the computer-simulated and phantom-measured voltages at the brain and skull layers were similar (except at excitation locations in the skull layer under the tDCS electrodes), and our gray matter electric field and potential distributions were consistent with previous computerized models. Furthermore, the circular tDCS electrodes led to greater electric field confinement in the different layers of the phantom compared to rectangular electrodes, as well as higher voltages at those layers [7].…”

“…In Phase I of this study [7], we developed a 3D head phantom model based on an MRI image stack of a healthy person allowing us to estimate electric current diffusion in tissues of different conductivity. We embedded 18 EEG monitoring electrodes into the model at skull and gray matter tissue layers and compared electric voltage measurements in phantom and computerized models before and after tDCS using different montages: Montage 1 (rectangular electrodes, bilateral DLPFC), Montage 2 (circular electrodes, left primary motor cortex [M1]-right supraorbital) and Montage 3 (circular electrodes, bilateral M1) [7]. We confirmed feasibility of the high-fidelity 3D head phantom model and also found high correlation between computer-simulated and phantommeasured voltages, especially at the brain level.…”

“…Computer simulations, while helpful, use oversimplified assumptions for tissue conductivities and do not reflect physiologic functions [5], [6]. We therefore aimed to quantify the effects of different tDCS montages in a phantom head model (Phase I - [7]) that could then be translated to humans (Phase II) to better understand their neurophysiological effects.…”

Improving the Effect of Transcranial Alternating Current Stimulation (tACS): A Systematic Review

“…Experiments are only part of the verification of the abovementioned optimization methods, and there are many studies that have explored the method and effect of optimization through computer simulation to explain the mechanism of optimization methods. Different models were established to determine whether electrical stimulation was effective and to optimize the number of electrodes and electrode arrangement (Morales-Quezada et al, 2019 ). Aberra established a computational model of human and rat cortical neurons to simulate the neural response of the cerebral cortex stimulated by electromagnetic fields (Aberra et al, 2018 ).…”

“…Compared with the classical electrode montage, the ring electrode montage can stimulate the target region more intensively and significantly reduce neurosensory side effects (Heise et al, 2016 ). In addition, studies found that circular electrodes have a better restraining effect on the electric field distribution of different phantom layers than rectangular electrodes (Morales-Quezada et al, 2019 ).…”