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 is calculated based on the measured voltage under the square wave current through the planar electrodes on the skin domain Ω. In the 2nd step, the m-th measured voltage is converted to a compensated voltage v * based on the voltage electrodes distance and threshold distance in order to highlight the region of interest of the dermis layer 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 in is successfully determined as increasing c on both simulations and experiments. The relationship between and c was evaluated by the determination coefficient R 2 and the normalized sensitivity The optimized with the highest evaluation values of 0.84 and 0.83 is under the condition of = 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.