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

In this study, sodium concentration in the dermis layer is imaged by the square wave open electrical impedance tomography (SW-EIT) with spatial voltage thresholding (SVT). The SW-EIT 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 voltageṽis calculated based on the measured voltagevunder the square wave currentIthrough the planar electrodes on the skin domain Ω. In the 2nd step, the-th measured voltagevis converted to a compensated voltagebased on the voltage electrodes distancedvand threshold distancedΓin order to highlight the region of interest of the dermis layerΩd.In the 3rd step, sodium concentration is imaged by the Gauss-Newton reconstruction method. The SW-EIT with SVT was applied to multi-layer skin simulation andexperiments under various dermis sodium concentrationsin the range of 5-50 mM. As an image evaluation result, the spatial mean conductivity distributionσ*inΩdis successfully determined as increasingon both simulations and experiments. The relationship between〈σ*〉andwas evaluated by the determination coefficientand the normalized sensitivity〈S〉.The optimizeddΓwith the highest evaluation values ofR2=0.84 and〈S〉=0.83 is under the condition ofdΓ= 2 mm. Based on the signal evaluation, the SW-EIT with SVT has a 15.32% higher correlation coefficientcompared to the conventionalEIT based on sinewave injection.