Computational Modelling of Probe Configurations for Electrical Impedance Spectroscopy-based Differentiation of Thyroid and Parathyroid Tissues

Abstract

Background: The ZedScan™ probe is an electrical impedance spectroscopy (EIS) device originally developed as a tool to diagnose Cervical Intraepithelial Neoplasia (CIN), recently explored as a potential tool to distinguish parathyroid glands from the surrounding tissues during surgery [1]. As reported, the relatively large size of the tip of the probe (5.5 mm) can be problematic to accurately cover and measure the impedance of small structures, such as parathyroid glands (3-7 mm). In this study, we will utilise a computational model to quantity the uncertainty associated with the probe misalignment and evaluate the benefits of reducing the size of the probe on thyroid and parathyroid differentiation. Materials and Methods: Multiscale finite element models of thyroid and parathyroid were developed to investigate the impact of the EIS measurement accuracy of various probe-parathyroid misalignment scenarios. Subsequently, the macroscale impedivity of thyroid and parathyroid tissues was simulated with smaller probe configurations to explore the benefits of probe optimisation. Results: The probe misalignment study reported up to 40%, 21% and 26% decrease in low-and high-frequency impedance and impedance frequency, respectively, compared to results with a desirable parathyroid-probe coverage. The decrease in parathyroid impedance brings the results closer to thyroid baseline EIS spectrum, reducing the feasibility of tissues separation. The probe optimisation study reported about 4% increase in parathyroid’s low-frequency impedance, showing a slight improvement in the thyroid and parathyroid differentiation. Conclusions: This study revealed the importance of the accuracy of the EIS measurement with the ZedScan™ device by demonstrating that imprecise parathyroid coverage could result in ‘contaminated’ measurements constraining their differentiation. Moreover, a smaller probe-tip design has the potential to further increase the ease of acquiring accurate parathyroid results, slightly improving the separation between the tissues on the basis of EIS measurements.