| Approaches for breast cancer detection and treatment that use microwave radiation show significant potential as low cost, non-ionizing technologies. The ability of emerging microwave-based techniques to selectively couple more strongly to diseased over normal tissues relies on the dielectric contrast between normal and malignant tissues. Contrast agents that selectively accumulate in tumors may significantly enhance the sensitivity of microwave techniques by altering the microwave scattering and absorption of malignant tissue. Ex vivo dielectric spectroscopy studies have shown the endogenous dielectric contrast between malignant and normal glandular/fibroconnective tissues is no more than approximately 10%. Since a vast majority of breast tumors originate in glandular tissue, the development of contrast agents is an important step towards establishing microwave-based modalities as clinically useful tools in breast cancer management.;The primary focus of this work is the investigation of the interaction of microwave-frequency electromagnetic waves with tissue-mimicking mixtures containing low-loss and lossy particles that are potential agents for enhancing the dielectric contrast between normal and malignant breast tissue. We present experimental and theoretical analyses of the impact of air-microbubbles, single-walled carbon nanotubes, and metallic nanoparticles on the dielectric properties of tissue-mimicking media. Our results indicate that air-microbubbles lower the dielectric properties and thermoacoustic response of tissue-mimicking mixtures, suggesting their potential role as contrast agents that reduce tumor properties. We show that carbon nanotubes, with their high aspect ratio, increase the dielectric properties and enhance the microwave heating response of tissue-mimicking materials. We conduct a theoretical analysis of microwave absorption in metallic nanoparticles and identify a regime in which metallic spherical nanoparticles may enhance the effective conductivity of malignant breast tissue. These investigations lay the foundation for future work in the emerging areas of contrast-enhanced microwave breast imaging and nanoparticle-assisted electromagnetic hyperthermia treatment of breast cancer.;Finally, we present a technique for fabricating anthropomorphic breast phantoms from oil-in-gelatin dispersions that mimic the dielectric properties of breast tissue over the 1 GHz to 6 GHz frequency range. The phantoms were heterogeneous, each with a skin layer and a complex network of fibroglandular and fatty tissues. These realistic phantoms may be used to validate microwave imaging systems. |
