Plantar Planar Dual-Array Electrical Impedance Tomography (PPDA-EIT) Method for Early Diabetic Foot Ulcers’ Detection

The relationship between impedance and the concentrations of glucose and L-tyrosine (TYR) has been clarified by the plantar planar dual-array electrical impedance tomography (PPDA-EIT) for early detection of diabetic foot ulcers (DFUs). PPDA-EIT images the electrical response changes of glucose and L-TYR at different concentrations in the DFU environment. In the experiments, the characteristic frequency was determined at the maximum impedance difference (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula>Z) by the electrochemical impedance spectroscopy (EIS) method. Optimal sensor location and size were determined based on analyzing the pressure concentration area during gait. The optimum electrode size and excitation method were found through 3-D electromagnetic simulation. Pork-mimic experiments were conducted to validate the sensor design by evaluating the image correlation coefficient (ICC) and the root mean square error (RMSE). From the EIS experimental results, glucose and L-TYR, as biomarkers for early DFUs’ detection, produced the largest impedance difference (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula>Z) at a measurement frequency of 1 MHz. From the 3-D electromagnetic simulation results, the most effective excitation involved the central electrode (sixth electrode), with the optimal electrode being a square with a side length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} = 8$ </tex-math></inline-formula> mm. The PPDA-EIT sensor was able to satisfactorily obtain reconstrued images of the object with an optimal ICC =0.8110 and RMSE =0.0982, which suggests that the approach used in this study provides an accurate indication of the glucose and L-TYR concentration change region in early DFUs.