The development of microwave breast cancer detection and treatment techniques has been driven by reports of substantial contrast in the dielectric properties of malignant and normal breast tissues. However, definitive knowledge of the dielectric properties of normal and diseased breast tissues at microwave frequencies has been limited by gaps and discrepancies across previously published studies. To address these issues, we conducted a large-scale study to experimentally determine the ultrawideband microwave dielectric properties of a variety of normal, malignant and benign breast tissues, measured from 0.5 to 20 GHz using a precision open-ended coaxial probe. Previously, we reported the dielectric properties of normal breast tissue samples obtained from reduction surgeries. Here, we report the dielectric properties of normal (adipose, glandular and fibroconnective), malignant (invasive and non-invasive ductal and lobular carcinomas) and benign (fibroadenomas and cysts) breast tissue samples obtained from cancer surgeries. We fit a one-pole Cole-Cole model to the complex permittivity data set of each characterized sample. Our analyses show that the contrast in the microwave-frequency dielectric properties between malignant and normal adipose-dominated tissues in the breast is considerable, as large as 10:1, while the contrast in the microwave-frequency dielectric properties between malignant and normal glandular/fibroconnective tissues in the breast is no more than about 10%.

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The efficacy of emerging microwave breast cancer detection and treatment techniques will depend, in part, on the dielectric properties of normal breast tissue. However, knowledge of these properties at microwave frequencies has been limited due to gaps and discrepancies in previously reported small-scale studies. To address these issues, we experimentally characterized the wideband microwave-frequency dielectric properties of a large number of normal breast tissue samples obtained from breast reduction surgeries at the University of Wisconsin and University of Calgary hospitals. The dielectric spectroscopy measurements were conducted from 0.5 to 20 GHz using a precision open-ended coaxial probe. The tissue composition within the probe's sensing region was quantified in terms of percentages of adipose, fibroconnective and glandular tissues. We fit a one-pole Cole-Cole model to the complex permittivity data set obtained for each sample and determined median Cole-Cole parameters for three groups of normal breast tissues, categorized by adipose tissue content (0-30%, 31-84% and 85-100%). Our analysis of the dielectric properties data for 354 tissue samples reveals that there is a large variation in the dielectric properties of normal breast tissue due to substantial tissue heterogeneity. We observed no statistically significant difference between the within-patient and between-patient variability in the dielectric properties.

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Homeland security and military defense technology considerations have stimulated intense interest in mobile, high power sources of millimeter-wave (mmw) to terahertz (THz) regime electromagnetic radiation, from 0.1 to 10THz. While vacuum electronic sources are a natural choice for high power, the challenges have yet to be completely met for applications including noninvasive sensing of concealed weapons and dangerous agents, high-data-rate communications, high resolution radar, next generation acceleration drivers, and analysis of fluids and condensed matter. The compact size requirements for many of these high frequency sources require miniscule, microfabricated slow wave circuits. This necessitates electron beams with tiny transverse dimensions and potentially very high current densities for adequate gain. Thus, an emerging family of microfabricated, vacuum electronic devices share many of the same plasma physics challenges that are currently confronting “classic” high power microwave (HPM) generators including long-life bright electron beam sources, intense beam transport, parasitic mode excitation, energetic electron interaction with surfaces, and rf air breakdown at output windows. The contemporary plasma physics and other related issues of compact, high power mmw-to-THz sources are compared and contrasted to those of HPM generation, and future research challenges and opportunities are discussed.

The development of ultrawideband (UWB) microwave diagnostic and therapeutic technologies, such as UWB microwave breast cancer detection and hyperthermia treatment, is facilitated by accurate knowledge of the temperature- and frequency-dependent dielectric properties of biological tissues. To this end, we characterize the temperature-dependent dielectric properties of a representative tissue type-animal liver-from 0.5 to 20 GHz. Since discrete-frequency linear temperature coefficients are impractical and inappropriate for applications spanning wide frequency and temperature ranges, we propose a novel and compact data representation technique. A single-pole Cole-Cole model is used to fit the dielectric properties data as a function of frequency, and a second-order polynomial is used to fit the Cole-Cole parameters as a function of temperature. This approach permits rapid estimation of tissue dielectric properties at any temperature and frequency.

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.

The finite difference time domain (FDTD) method is widely used as a computational tool for development, validation, and optimization of emerging microwave breast cancer detection and treatment techniques. When expressed in terms of Debye parameters, dispersive breast tissue dielectric properties can be efficiently incorporated into FDTD codes. Previously, we experimentally characterized the dielectric properties of a large number of excised normal and malignant breast tissue samples from 0.5 to 20 GHz. We subdivided the large database of normal tissue data into three groups based on the percent adipose tissue present in a particular sample. In addition, we formed a group of all cancer samples that contained at least 30% malignant tissue. We summarized the data using one-pole Cole-Cole models that were rigorously fit to the median dielectric properties of the three normal tissue groups and one malignant tissue group. In this letter, we present computationally simpler one-and two-pole Debye models that retain the high accuracy of the Cole-Cole models. Model parameters are derived for two sets of frequency ranges: the entire measurement frequency range from 0.5 to 20 GHz, and the 3.1-10.6 GHz FCC band allocated for ultrawideband medical applications. The proposed Debye models provide a means for creating computationally efficient FDTD breast models with realistic wideband dielectric properties derived from the largest and most comprehensive experimental study conducted to date on human breast tissue.Index Terms-Breast cancer detection and treatment, Cole-Cole model, Debye model, dielectric properties, finite-difference timedomain (FDTD).