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 dv and threshold distance dG in order to highlight the region
of interest of the dermis layer .dW 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 *sá ñ in dW is successfully
determined as increasing c on both simulations and experiments. The relationship between *sá ñand c
was evaluated by the determination coefficient R2 and the normalized sensitivity S .á ñ The optimized
dG with the highest evaluation values of R2 = 0.84 and Sá ñ = 0.83 is under the condition of
dG = 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.
