Bivariate polynomial for time-dependent dielectric properties of ex-vivo porcine and human liver tissue at frequencies below 100 MHz

Time-dependent dielectric properties of ex vivo tissue are important for biological viability assessment, successful organ transplantation and finding the optimal substitute for the in vivo tissue. However, there are relatively few studies on the time dependence of dielectric properties and especially the mathematical models related to it. This study mathematically describes the time-dependent dielectric properties of excised liver tissues at frequencies below 100 MHz. A bivariate high-order polynomial was used to reflect the mathematical correlation of dielectric properties (relative permittivity ε and conductivity σ ) with frequency and ex vivo time under controlled temperature and humidity. Statistical analysis, cross validation and error analysis were used to assess the fitting performance and prediction ability of the bivariate high-order polynomial fitting model. The results showed that the dielectric properties of excised porcine liver tissues and human liver tissues could be well fitted and predicted by the bivariate high-order polynomial fitting model at frequencies below 100 MHz. Encouragingly, the dielectric properties can be calculated at a given frequency and ex vivo time at controlled temperature and humidity. This presents a new way of obtaining accurate dielectric properties of ex vivo biological tissues in a specific outer environment. It is also possible to extrapolate back the ex vivo time after excision from the body using the dielectric properties.