Investigation of histology radius for dielectric characterisation of heterogeneous materials

Abstract

Knowledge of the dielectric properties of biological tissues is fundamental in the design of novel electromagnetic-based medical devices. Tissue dielectric properties are typically measured using the open-ended coaxial probe technique, which is designed for homogeneous samples. Histological analysis may be conducted to associate the measured dielectric properties to different tissue types within heterogeneous samples. However, the histology radius (i.e., the radial extent of the tissue sample that undergoes histological analysis) has not been consistently defined in the literature; therefore, this parameter may be a source of error in dielectric data. For this reason, we investigate the histology radius of various heterogeneous samples. Dielectric measurements were conducted over the frequency range of 0.5 to 20 GHz on radially heterogeneous tissuemimicking materials and biological tissues, with different dielectric properties and contrasts. The experimental results were validated with numerical simulations and indicate that: i) the histology radius does not exceed the probe radius; ii) the dielectric properties of radially heterogeneous tissues depend on the spatial distribution of each material within the histology radius; and iii) the bulk dielectric properties of concentric heterogeneous tissues highly depend on the properties of each constituent material within the histology radius. This study supports consistent identification of the histology radius and provides a basis for rigorous interpretation of the dielectric properties of heterogeneous tissues.

Development of an Anthropomorphic Phantom of the Axillary Region for Microwave Imaging Assessment

“…The size of ALNs ranged approximately from 5 mm to 2 cm on their longer axis, whereas their thickness varied approximately between 4 mm and 7 mm. These thickness values are greater than the sensing depth of the probe which has been estimated to vary between 2 and 3 mm, as reported in Reference [ 41 , 42 ]. The excised ALNs were embedded in fat tissue which was removed by the surgeons as much as possible.…”

Challenges of Post-measurement Histology for the Dielectric Characterisation of Heterogeneous Biological Tissues

“…A key difficulty in linking the dielectric measurements to the histological results is the need for the identification of a "histology region", i.e., a region demarcated on the histological images that includes the tissues that may have contributed to the measured dielectric properties. The definition of the histology region is challenging because it requires knowledge of the sensing volume of the measurement probe, which is delineated by sensing radius and sensing depth [16,17].…”

“…While recent studies have investigated the sensing radius and sensing depth of several coaxial probes [16,17], there are no studies in the literature that have investigated the post-measurement histology process and its impact on the definition of the histology region. Furthermore, in all dielectric studies investigating the dielectric properties of heterogeneous tissue samples with histology to date, the histology region has been defined by directly applying the sensing volume findings without taking into account the change in tissue morphology caused by the histological process [18].…”

“…In particular, this study involves dielectric measurement and post-measurement histology of heterogeneous tissue samples from different animals and different regions of the body. Furthermore, in this study, the sensing radius and tissue dielectric contribution findings from previous dielectric studies [17,19,20] are considered in order to evaluate the applicability of these findings in defining the histology region and in accurately interpreting the measured dielectric properties. The specific findings of each of these studies is discussed in the relevant sections below in relation to the results of this work.…”

“…Specifically, the landmark location that can be marked is the interface between tissue types. Similarly to the samples analysed in [17,19,20], each of the samples has a structure that does not vary with depth and consists of two tissue types, which have an interface parallel to the axis of the probe and perpendicular to the surface of the sample. In particular, ten samples were selected as representative radially heterogeneous samples to be analysed by post-measurement histology.…”