Sodium concentration imaging in dermis layer by square-wave open electrical impedance tomography (SW-oEIT) with spatial voltage thresholding (SVT)

Abstract

In this study, sodium concentration in the dermis layer is imaged by the square wave open electrical impedance tomography (SW-oEIT) with spatial voltage thresholding (SVT). The SW-oEIT with SVT consists of three steps which are (1) voltage measurement, (2) spatial voltage thresholding, and (3) sodium concentration imaging. In the 1st step, the root mean square voltage v ̃ is calculated based on the measured voltage v under the square wave current I through the planar electrodes on the skin domain Ω. In the 2nd step, the m-th measured voltage v is converted to a compensated voltage v * based on the voltage electrodes distance d v and threshold distance d Γ in order to highlight the region of interest of the dermis layer Ω d . In the 3rd step, sodium concentration is imaged by the Gauss-Newton reconstruction method. The SW-oEIT with SVT was applied to multi-layer skin simulation and ex-vivo experiments under various dermis sodium concentrations c in the range of 5-50 mM. As an image evaluation result, the spatial mean conductivity distribution σ * in Ω d is successfully determined as increasing c on both simulations and experiments. The relationship between 〈 σ * 〉 and c was evaluated by the determination coefficient R 2 and the normalized sensitivity 〈 S 〉 . The optimized d Γ with the highest evaluation values of R 2 = 0.84 and 〈 S 〉 = 0.83 is under the condition of d Γ = 2 mm. Based on the signal evaluation, the SW-oEIT with SVT has a 15.32% higher correlation coefficient CC compared to the conventional oEIT based on sinewave injection.