Numerical Sensitivity Analysis for Dielectric Characterization of Biological Samples by Open-Ended Probe Technique.

Marta Cavagnaro,Giuseppe Ruvio

doi:10.3390/s20133756

Abstract

Dielectric characterization of biological tissues has become a fundamental aspect of the design of medical treatments based on electromagnetic energy delivery and their pre-treatment planning. Among several measuring techniques proposed in the literature, broadband and minimally-invasive open-ended probe measurements are best-suited for biological tissues. However, several challenges related to measurement accuracy arise when dealing with biological tissues in both ex vivo and in vivo scenarios such as very constrained set-ups in terms of limited sample size and probe positioning. By means of the Finite Integration Technique in the CST Studio Suite® software, the numerical accuracy of the reconstruction of the complex permittivity of a high water-content tissue such as liver and a low water-content tissue such as fat is evaluated for different sample dimensions, different location of the probe, and considering the influence of the background environment. It is found that for high water-content tissues, the insertion depth of the probe into the sample is the most critical parameter on the accuracy of the reconstruction. Whereas when low water-content tissues are measured, the probe could be simply placed in contact with the surface of the sample but a deeper and wider sample is required to mitigate biasing effects from the background environment. The numerical analysis proves to be a valid tool to assess the suitability of a measurement set-up for a target accuracy threshold.

Highlights

In recent years, the rapid growth of medical applications based on electromagnetic (EM) fields such as hyperthermic treatments [1,2,3], medical imaging [4], on-body and implant-based communications [5]has focused a strong interest in the accurate dielectric characterization of biological tissues
It can be noted that the insertion depth of the probe is the most critical parameter which affects the accuracy of the reconstructed complex permittivity of a material under test (MUT) with high water content
Comparing results from a sample of 70 mm height, 15 mm width in which the probe is placed in contact with the surface (0 insertion depth) with those of a sample 6 mm high, 5 mm wide, in which the probe is inserted for 1 mm only (Table 2, case 4 vs. 17), it can be noted that the error is greater in the bigger sample for both the real and imaginary part of the complex permittivity (2.8 vs. 2.5; 9.4 vs. 6.1)

Summary

Introduction

The rapid growth of medical applications based on electromagnetic (EM) fields such as hyperthermic treatments [1,2,3], medical imaging [4], on-body and implant-based communications [5]has focused a strong interest in the accurate dielectric characterization of biological tissues. Dielectric properties of tissues mediate the interaction between EM fields and the human body, and their values as well as the way these values change e.g., as a function of frequency, tissue status, temperature, are critical in the different applications [3,6]. Enhanced knowledge of the dielectric properties of human tissues and how these parameters change with time, temperature, hydration, and blood perfusion can inform the design of safer and more efficacious therapeutic, diagnostic and theranostic EM-based devices It was in 1984 when Joines [10] reported that diseased tissues show different dielectric values from healthy ones, giving momentum to the search of new techniques based on interaction of EM fields. The dielectric characterisation can be used to monitor thermal ablation treatments which induce loco-regional coagulative necrosis and a consequent dramatic dehydration of the targeted body region [6,21]

Results

Discussion

Conclusion