Modeling of the dielectric properties of biological tissues within the histology region

The dielectric properties of biological tissues characterize the interaction of electromagnetic fields with the human body. As such, accurate knowledge of these properties is vital to the design and development of electromagnetic medical technologies. Despite their importance, the reported dielectric properties of key tissues have been inconsistent across studies. The natural heterogeneity of tissue has been identified as a contributing factor to these inconsistencies. In order to attribute dielectric properties to heterogeneous tissues, histological analysis is conducted to determine which tissue types contribute to the dielectric measurement. However, the Histology Region, i.e., the volume of the tissue sample that undergoes histological analysis, and the region corresponding to the dielectric measurement, has not been well-defined. Thus, instead of reducing uncertainties, more questions have been raised about the accuracy of data: if the Histology Region is not identified correctly, then the corresponding dielectric measurement does not represent the actual tissues involved. In this work, we examine the longitudinal extent of the Histology Region (i.e., the histology depth) for various heterogeneous samples composed of phantoms and biological tissues. This study highlights the fact that the relationship between the volume of tissue in a sample and the contribution of that tissue to the measured dielectric properties is not linear. Assuming that this relationship is linear may be a significant source of error in dielectric data. Further, we model, for the first time, the nonlinear relationship between the contribution of individual tissues to the dielectric measurement and the volume that each tissue occupies within the bulk sample. This work enables prediction of the permittivity of a sample with longitudinal heterogeneities, given knowledge of the constituent tissues of the sample, and provides the basis for modeling of all types of heterogeneities. These results will contribute to the minimization of uncertainties in the dielectric measurement of heterogeneous tissues.