Volume sensing properties of open-ended coaxial probes for dielectric spectroscopy of breast tissue

An ultrawideband microwave imaging approach to early breast cancer detection is based on the hypothesis that there exists a significant dielectric-properties contrast between cancerous and normal breast tissue at microwave frequencies. Definitive knowledge of the dielectric properties of breast tissue in the RF/microwave frequency range (0.1-20 GHz) is required for the development of novel technologies related to the detection and treatment of breast cancer. Coaxial probes have been extensively analyzed and used in dielectric spectroscopy. A careful analysis of the sensing volume of the probes used in our measurements on excised specimens is needed to ensure the highest possible accuracy in the dielectric properties estimates of human breast tissue. We present preliminary estimates of the sensing volume of small diameter coaxial probes. Results were obtained for 2.20 mm and 3.58 mm diameter probes, both without flanges. De-ionized water, methanol, and butanol were chosen as test liquids because their dielectric properties cover the expected range of permittivities of breast tissue. Our results suggest that relatively small tissue samples are sufficient to establish accurately their dielectric properties in the microwave frequency range up to 20 GHz, using small-diameter open-ended coaxial probes.