Flexible-Center Hat Complete Electrode Model for EEG Forward Problem

Flexible-Center Hat Complete Electrode Model for EEG Forward Problem

Flexible-Center Hat Complete Electrode Model for EEG Forward Problem 789 444 IEEE Transactions on Biomedical Engineering (TBME)
Author(s): Ting Zhang, Yan Liu, Erfang Ma, Bo Peng, Ardalan Aarabi, Siqi Zhang, Ying Hu, Jing Xiang, and Yakang Dai

The EEG forward problem (FP) is to simulate the electric potential on the scalp that is generated by the hypothetical intracranial current sources, whose accurate solution provides a basic model for EEG source analysis. The accuracy of FP solution relies heavily on realistic models of the head, source, and electrode. This study aims to develop a more realistic electrode model (i.e., flexible-center hat complete electrode model, FCH-CEM) for FP, by integrating the electrode structure into the construction of the distribution of electrode contact conductance (ECC). Firstly, based on the law of resistance and the electrode structure, a hat-shaped ECC is analyzed and further characterized by the hat function; Secondly, this hat function is modified by two parameters, offset ratio and offset direction, to account for the flexible-center hat-shaped ECC due to the difference of electrode structures between different EEG caps. Finally, this function is introduced to the electrode modeling and further to the solution of FP.

The finite element simulation results based on the realistic head model demonstrate that compared with the two existing electrode models, the point electrode model (PEM), and the traditional complete electrode model (CEM), the proposed FCH-CEM can achieve a significant adjustment of the scalp potential distribution, and has the potential to improve the accuracy of the FP solution, especially when the contact conductance is located in the range of 10-3S/m2 to 10-1S/m2 (corresponding to the electrode equivalent resistances of 5, 090 kΩ to 31.8 kΩ); the proposed method is more robust compared to PEM when the mesh resolution is reduced to 2 mm. Further experiments indicate the significance of considering the shunting effects, as ignoring them results in larger errors than mesh-resolution reduction when the average contact conductance is large (101S/m2).

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