Sensing volume of open-ended coaxial probes for dielectric characterization of breast tissue at microwave frequencies

Abstract

Abstract-We are using open-ended coaxial probes to determine the dielectric properties of freshly excised normal and diseased breast tissue specimens. The considerable variability in size and composition of these specimens predicates the need for determining the minimum surgical specimen size that yields accurate measurements for a given probe diameter. We investigate the sensing volume of 2.2-and 3.58-mm-diameter flange-free coaxial probes for both low-and high-water-content tissue using standard liquids that exhibit dielectric properties similar to breast tissue over the microwave frequency range from 1 to 20 GHz. We also present an innovative graphical technique based on the use of Cole-Cole diagrams to determine the error thresholds in the magnitude and phase of the reflection coefficient, which bound the errors in the measured complex permittivity to an acceptable level. Results from self-consistent experiments and finite-difference time-domain simulations indicate that a tissue specimen with a thickness of 3.0 mm and a transverse dimension of 1.1 cm is the minimum size that yields accurate measurements with the 3.58-mm-diameter probe. For the 2.2-mm-diameter probe, the specimen's thickness and width should be at least 1.5 and 5 mm, respectively. These conclusions are relevant not only to breast tissue characterization, but also more generally to the dielectric characterization of a variety of low-and high-water-content biological tissues.

In Vivo Dielectric Properties of Healthy and Benign Rat Mammary Tissues from 500 MHz to 18 GHz

“…The slim form probe has an aperture diameter of 2.2 mm. The sensing depth of the custom made probe with 2.2 mm aperture is reported to be between 0.75 and 1.5 mm in homogeneous materials [17]. Similarly, the sensing depth of the slim form probe is reported to be between 1.05 and 1.41 mm for homogeneous materials [18].…”

Assessing Changes in Dielectric Properties Due to Nanomaterials Using a Two-Port Microwave System

“…These tissue characterisation studies show variation in dielectric measurements, which can be explained by the sample preparation and measurement technique. The accuracy of dielectric spectroscopy [10,11] and the impact of the tissue sample's hydration level [12,13] complicate further the goal of assessing tissue contrast based on dielectric spectroscopy measurements. Indeed, tissue hydration can pose challenges in producing consistent dielectric measurements, as it can affect the complex dielectric constant.…”