Sodium concentration imaging in dermis layer by square-wave open electrical impedance tomography (SW- o 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- o EIT) with spatial voltage thresholding (SVT). The SW- o 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 m -th measured voltagevis converted to a compensated voltage v * based 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- o EIT 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 distributionσ*inΩdis 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 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- o EIT with SVT has a 15.32% higher correlation coefficient CC compared to the conventional o EIT based on sinewave injection.