Exposure of Tissue Mimicking Materials Based on Conductive Polyurethane to Vacuum During Pot Time Significantly Reduces their Electric Impedance

Studies dealing with methodological uncertainties using electrical impedance tomography can advantageously use technical phantoms for their measurements. Using a phantom for measurement can eliminate variability in a living subject. In addition, the phantom can be assembled specifically for the needs of a given specific measurement. Time-stable phantoms for EIT can be made from a mixture of polyurethane, carbon black and graphite powder. In the preparation of this type of phantom, inhomogeneities in the form of air bubbles may occur in the material. The aim of this study was to determine the effect of evacuation during pot time and pressurization during polymerization on the tissue mimicking material impedance. Four groups of tissue mimicking materials samples were created. The control group did not receive any treatment. The second group was placed in a compressed air atmosphere (1.5 bar) during the polymerization. The third group was exposed to a vacuum of -0.75 bar during the pot time. The fourth group was evacuated during the pot time and placed under air pressure during the polymerization. Based on impedance measurements, the fundamental effect of vacuum degassing was found. Exposure of the samples to vacuum reduced the impedance of the samples more than tenfold. The effect of pressure polymerization on impedance reduction was also demonstrated to be statistically significant. However, it was substantially less than the effect of vacuum exposure.