Dielectric Properties Of Breast Tissues Research Articles

Low-cost device for breast cancer screening: A dry setup IR-UWB proposal

This paper presents a dry-setup microwave imaging apparatus proposal aiming at breast cancer detection, seeking low-cost and portability. In 2020, breast cancer overtook lung cancer as the most commonly diagnosed worldwide, and its impact on low-income countries has encouraged the development of non-invasive and affordable screening equipment; its use could reduce mortality rates by scaling up early detection reach. A US$ 150.00 microwave transceiver platform with embedded antennas was employed to maintain costs down, while a dry-coupling silicone rubber bra was used to keep the device portable. Firstly, a front-end power loss study and simulations by utilizing a finite integration technique software were carried out to analyse the proposed hardware power ability to detect tumours depth in the breast. Secondly, microwave signals were transmitted, illuminating a developed phantom that mimics the dielectric properties of breast tissues. The resulting images were generated by applying collected backscattered signals to a delay and sum algorithm whereby improvements were implemented aiming at enhancing tumour contrast. Simulated and experimental results employing the system proposed and the phantom presented signal to clutter and signal to mean ratio above 6.0 dB and 22.0 dB, respectively, and average tumour location precision of 0.5 cm. The results demonstrated the proposed apparatus potential to prospect a low-cost and portable system for first approach breast cancer screening. Although more investigations and additional implementations are still necessary for conducting clinical trials, the proposals presented have paved the way to a resource-limited screening equipment development in the future.

Temperature dependence studies of tissue-mimicking phantoms for ultra-wideband microwave breast tumor detection

Microwave imaging (MWI) systems are being investigated for breast cancer diagnostics as an alternative to conventional x-ray mammography and breast ultrasound. This work aims at a next generation of tissue-mimicking phantoms modelling the temperature-dependent dielectric properties of breast tissue over a large frequency bandwidth. Such phantoms can be used to develop a novel kind of MWI systems that exploit the temperature-dependent permittivity of tissue as a natural contrast agent. Due to the higher water content in tumor tissue, a temperature increase leads to a different change in the complex permittivity compared to surrounding tissue. This will generate a tumor dominated scattering response when the overall tissue temperature increases by a few degrees, e.g. through the use of microwave hyperthermia systems. In that case a differential diagnostic image can be calculated between microwave measurements at reference (around 37 °C) and elevated temperature conditions. This work proposes the design and characterization of agar-oil-glycerin phantoms for fatty, glandular, skin and tumor tissue. The characterization includes measurements with an open-ended coaxial probe and a network analyzer for the frequency range from 50 MHz to 20 GHz in a temperature-controlled environment covering the temperature range from 25 °C to 46 °C. The phantoms show an unique temperature response over the considered frequency bandwidth leading to significant changes in the real and imaginary part of the complex permittivity. Comparative studies with porcine skin and fat tissue show a qualitative agreement.

Application of the migration method for radiotomography of breast cancer

A new method to visualize microwave image is presented to early non-invasive detection of breast cancer tumors. A new processing method to compute microwave images of heterogeneity in a biological environment is described here, as well as a new algorithm for accelerating the calculation of three-dimensional radio images. Sounding of synthetic phantoms with dielectric properties of breast tissue was carried out in the range of 2–8 GHz using a special radar system developed by the authors. Results show that it is possible to use this microwave imaging method to form 3D accurate images using hemispherical scan Images of tumor phantoms were obtained during probing in the 2–8 GHz range with a resolution of about 5–7 mm.According to the results of the reconstruction of three-dimensional radio images, it was revealed that the calculation time can be reduced by at least 2 times with an insignificant loss of quality.

Terahertz Imaging for Breast Cancer Detection.

Terahertz (THz) imaging has the potential to detect breast tumors during breast-conserving surgery accurately. Over the past decade, many research groups have extensively studied THz imaging and spectroscopy techniques for identifying breast tumors. This manuscript presents the recent development of THz imaging techniques for breast cancer detection. The dielectric properties of breast tissues in the THz range, THz imaging and spectroscopy systems, THz radiation sources, and THz breast imaging studies are discussed. In addition, numerous chemometrics methods applied to improve THz image resolution and data collection processing are summarized. Finally, challenges and future research directions of THz breast imaging are presented.

An Implantable Antenna Sensor for Medical Applications

Pathological changes of human tissues, such as tumors, can cause changes in the dielectric properties of the tissues. Based on this characteristic, we propose an implantable antenna sensor and study its radiation and sensing performance in breast tumor recurrence diagnosis in the 2.45 GHz Industrial, Scientific, and Medical (ISM) band. The antenna sensor shows the advantage of miniaturization with a volume of 13.2mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> by employing an S-shape monopole antenna and a closed loop. The simulated results show that the antenna sensor has a good radiation pattern with peak gain values of -8.4 and -17.9dBi in normal and malignant breast tissue, respectively. Furthermore, the antenna sensor exhibits good sensitivity to the dielectric properties of breast tissue. When the permittivity increases by 10, the resonance frequency decreases between 9-18MHz. To verify the simulated results, the sensing properties and the radiation patterns of the implantable antenna sensor were measured in the pork and tissue-mimicking liquid. The measured results are consistent with the simulated ones. Hence, the proposed antenna can be used as a wireless sensor to monitor pathological changes of human tissues, such as breast tumors.

Computational FEM Model and Phantom Validation of Microwave Ablation for Segmental Microcalcifications in Breasts Using a Coaxial Double-Slot Antenna.

Introduction Cancer is the second leading cause of death worldwide. Breast cancer is the second most common cause of cancer-related mortality, accounting for 11.6% of the total number of deaths. The main treatments for this disease are surgical removal of the tumor, radiotherapy, and chemotherapy. Recently, different minimally invasive technologies have been applied (e.g., emission of electromagnetic waves, thermal and chemical means) to overcome the important side effects of these treatment modalities. The objective of this study was to develop and evaluate a predictive computational model of microwave ablation. Materials and Methods The predictive computational model of microwave ablation was constructed by means of a dual-slot coaxial antenna. The model was compared with an experiment performed using a breast phantom, which emulates the dielectric properties of breast tissue with segmental microcalcifications. The standing wave ratio (SWR) was obtained for both methods to make a comparison and determine the feasibility of applying electromagnetic ablation to premalignant lesions in breasts. Specifically, for the analysis of segmental microcalcifications, a breast phantom with segmental microcalcifications was developed and two computational models were performed under the same conditions (except for blood perfusion, which was excluded in one of the models). Results The SWR was obtained by triplicate experiments in the phantom, and the measurements had a difference of 0.191 between the minimum and maximum SWR values, implying a change of power reflection of 0.8%. The average of the three measurements was compared with the simulation that did not consider blood perfusion. The comparison yielded a change of 0.104, representing a 0.2% change in power reflection. Discussion. Both experimentation in phantom and simulations demonstrated that ablation therapy can be performed using this antenna. However, an additional optimization procedure is warranted to increase the efficiency of the antenna.

Accurate construction of 3-D numerical breast models with anatomical information through MRI scans

The realistic numerical breast model is an important tool for verifying algorithms, improving design concepts, and exploring new technologies related to microwave breast cancer detection. Recently, several numerical breast models have been developed. However, these models do not include the real breast boundary and the chest region, which causes the electromagnetic wave propagation in the breast models to deviate from the actual situation. The proposed breast models in this paper overcome the significant deficiencies of the recent breast models in terms of structure completeness and authenticity. The model construction based on magnetic resonance imaging (MRI) scans is a multistep approach. Firstly, intensity inhomogeneity in MRI images is corrected by an improved nonparametric nonuniform intensity normalization (N4) algorithm. Then, a dual threshold and morphological transformation (DTMT) method is developed to segment the real breast region. Subsequently, a modified maximum inter-class variance (MICV) method is employed to automatically divide the breast region into the fat and the fibroglandular clusters with desired complexity. Finally, the dielectric properties of breast tissues are calculated by a piecewise weighted mapping method. The applicability and effectiveness of the proposed method are verified by constructing four breast models with varying tissue density, shape, and size. The constructed models in this study are significant to achieve reliable and precise effects for microwave breast cancer detection due to the accurate expression of the breast anatomical information and electromagnetic characteristics.

A Pilot Study of the Impact of Microwave Ablation on the Dielectric Properties of Breast Tissue.

Percutaneous microwave ablation (MWA) is a promising technology for patients with breast cancer, as it may help treat individuals who have less aggressive cancers or do not respond to targeted therapies in the neoadjuvant or pre-surgical setting. In this study, we investigate changes to the microwave dielectric properties of breast tissue that are induced by MWA. While similar changes have been characterized for relatively homogeneous tissues, such as liver, those prior results are not directly translatable to breast tissue because of the extreme tissue heterogeneity present in the breast. This study was motivated, in part by the expectation that the changes in the dielectric properties of the microwave antenna’s operation environment will be impacted by tissue composition of the ablation target, which includes not only the tumor, but also its margins. Accordingly, this target comprises a heterogeneous mix of malignant, healthy glandular, and adipose tissue. Therefore, knowledge of MWA impact on breast dielectric properties is essential for the successful development of MWA systems for breast cancer. We performed ablations in 14 human ex-vivo prophylactic mastectomy specimens from surgeries that were conducted at the UW Hospital and monitored the temperature in the vicinity of the MWA antenna during ablation. After ablation we measured the dielectric properties of the tissue and analyzed the tissue samples to determine both the tissue composition and the extent of damage due to the ablation. We observed that MWA induced cell damage across all tissue compositions, and found that the microwave frequency-dependent relative permittivity and conductivity of damaged tissue are lower than those of healthy tissue, especially for tissue with high fibroglandular content. The results provide information for future developments on breast MWA systems.

Use of multi-angle ultra-wide band microwave sounding for high resolution breast imaging.

This report proposes an approach to develop a method of microwave imaging for early, non-invasive diagnosis of breast tumors. Here we describe a data-processing method for obtaining radio images of biological heterogeneities and a new method for filtering static noise in received signals. A specialized radar system was developed in the present study and used to perform sounding of synthetic phantoms with the dielectric properties of breast tissue in the range of 2-8GHz. Datasets thus contained synthetic structures that imitated the dielectric properties of breast tissues and tumors. The permittivity values of the created artificial materials were verified using a waveguide cell. Tumors were simulated via plastic balls with a diameter of 1cm that were filled with saline. A special ultra-wide band (UWB) radar system developed at Tomsk State University was used to register radar responses from the phantoms. The radar system included the vector reflectometer, the UWB antenna, and the mechanical scanner that provided sounding in the hemisphere. We also used the time-domain signals processing method to obtain the radio image signals. In this method, all signals received during scanning in the hemisphere are added with calculated delay for the given focus point. Special filtering of the constant components of the signal at each of the angular sounding latitudes was used to eliminate clutter in the received signal. This solution allowed us to account for additive clutter in the received signal from structural elements during scanning in the hemisphere. The influence of the number of angles on the quality of the resulting radio image was evaluated. The phantoms of a female breast and a malignant tumor from artificial materials with electrophysical characteristics close to those of real tissues have been developed. This facilitated verification of the proposed method for constructing radio images under more clinically relevant conditions. The proposed filtering of the constant components of the signal effectively doubled the signal-to-noise ratio in the resulting radio image compared with the standard algorithm of clutter filtering. The influence of different numbers of scan points on the quality of the final radio image are presented herein. It is concluded that it is sufficient to use not more than 600-800 sounding points for acceptable image quality. A further increase in the number of angles does not significantly improve image quality despite increasing the scan time. Scanning in the hemisphere of the breast phantom using the proposed method of clutter filtering show that multi-angle microwave imaging can form accurate three-dimensional (3D) images with double the level of signal-to-clutter compared with the standard filtering approach. The images of artificial tumors were obtained when sounding in the range of 2-8GHz with the resolution of about 5-7mm.

Abstract OT3-04-01: Feasibility of incorporating miniaturized, flexible radiofrequency (RF) sensors in a breast biopsy needle for accurate real-time characterization of benign and malignant tissue

Abstract Background: With approximately 1.6 million annual procedures in the United States and 3 million world-wide, needle biopsy is considered the Gold Standard for breast cancer diagnosis and treatment planning. Overdiagnosis can result in unnecessary treatment, cost, and anxiety, while underdiagnosis can delay treatment and diminish outcomes. A 2015 study published in JAMA1 found nearly 25% discordance between pathology diagnosis and expert review, most pronounced in cases of DCIS, Atypia and in patients with dense breasts. It has been well established that physiologic differences between benign and malignant tissues are reflected in their electrical properties.2,3,4 Access to real-time tissue properties during the biopsy procedure has the potential for increasing accuracy by enabling the most suspicious tissue to be sampled, and by providing the tissue characterization to pathology for comparison with histologic findings. Through research made possible by the European Union’s Horizon 2020 research award, this feasibility study sought to determine if five 0.8mm miniaturized, flexible RF sensors (Dune Medical Devices, Alpharetta, GA) mounted within the sample cavity of a 14-gauge biopsy needle can accurately measure and map the electrical properties of multiple breast tissue types. Methods: Between March, 2018 and March, 2019, 44 patients undergoing mastectomy or lumpectomy at three medical centers in Israel were enrolled in the study. The biopsy needle was applied to freshly excised specimens, with continuous readings by the sensors. An average of 8.1 cores (ranging from 2-10) were obtained from each specimen. Cores were oriented and analyzed by standard histopathology. Based on histology, the dielectric properties of the various tissue types were derived, and the ability of the device to differentiate between malignant and non-malignant tissue was assessed. Results: A total of 357 cores from 44 specimens were analyzed. Ease of use and quality of tissue samples were equivalent to that of a standard biopsy needle. The dielectric properties of three tissue groups: Fat, Healthy non-Fat, and Malignant, in the low radiofrequency range were measured, showing distinct differences between the various types. Feature sizes larger than 0.8 mm were analyzed. The differentiation ability between tissue types was characterized using sensitivity and specificity of 85% and 99% respectively. Conclusions: Miniature, flexible RF sensors can be incorporated onto a biopsy needle. Although this study utilized a 14-gauge core needle, the 0.8mm sensor size allows for configuration within both vacuum-assisted and core biopsy needles of various gauges. The dielectric properties of breast tissue can be assessed in real-time during the biopsy procedure. These results show promise in differentiating between breast tissue types, specifically cancerous and benign, enabling more accurate tissue sampling and subsequent diagnosis. Improving the accuracy of breast biopsies should provide immediate clinical impact by reducing overstaging and subsequent unneeded treatment, procedures and cost, as well as reducing understaging of breast cancer which results in delayed diagnosis and missed cancer. Forward-looking, real-time tissue characterization during biopsy could prove especially beneficial should newer protocols currently under trial, such as active surveillance for low risk DCIS5 and omission of surgery for exceptional responders of neoadjuvant chemotherapy,6 become treatment options. The ability to mount the sensors to minimally invasive treatment devices will lay the foundation for expanding the technology to other cancer types, with the potential for precision delivery of new targeted drugs, radiation and ablation therapies at the site of the cancer. Citation Format: Noemi Weisenberg, Avihai Lachman, Lisa Cadena, Inbal Shimens, Olga Shmain, Ahuva Grubstein, Yael Rapson, Hana Cernik, Debora Kidron, Tania Zehavi, Evgeny Edelstein, Vladimir Kravtsov, Tatiana Kogan, Meirav Wolff Bar, Judith Diment, Ilana Haas, Patricia Malinger, Eran Sharon, Yehudit Birnbaum, Ada Magen, Yael Sobol, Osnat Givon Madhala, Sonya Wadhawker, Tanir M Allweis. Feasibility of incorporating miniaturized, flexible radiofrequency (RF) sensors in a breast biopsy needle for accurate real-time characterization of benign and malignant tissue [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT3-04-01.

Near-Field Microwave Loop Array Sensor for Breast Tumor Detection

In this work, we propose the use of loop antenna arrays excited by a single port as a microwave sensor for near-field microwave breast tumor detection. The proposed sensor has a high sensitivity to detect an abnormality in the dielectric properties of breast tissues. The existence of the breast tumors is detected by estimating the variations in the response of the reflection coefficient of the sensor for both tumours and healthy cases. The developed sensor comprises 4-element identical loop antenna array fed with a single port, the use of antenna array enlarges the sensitivity area as compared to a single element resulting in better detection of tumors located deeply inside breast tissues. Numerical simulations have been conducted using a numerical breast model with and without tumor cells placed in the near-field of the sensor. The sensor is capable of detecting a breast tumor inserted at five different locations and with various sizes. An experimental validation was conducted using a glass box filled with vegetable oil and metallic spheres that resembles healthy and tumourous breast tissues, respectively. The simulation and experimental results show that the array sensor has a high sensitivity for detecting a metallic sphere placed at five different locations inside a dielectric medium as well as detecting variable sizes of the metallic spheres.

Towards mm-wave spectroscopy for dielectric characterization of breast surgical margins

PurposeThe evaluation of the surgical margin in breast conservative surgery is a matter of general interest as such treatments are subject to the critical issue of margin status as positive surgical margins can undermine the effectiveness of the procedure. The relatively unexplored ability of millimeter-wave (mm-wave) spectroscopy to provide insight into the dielectric properties of breast tissues was investigated as a precursor to their possible use in assessment of surgical margins. MethodsWe assessed the ability of a mm-wave system with a roughly hemispherical sensitive volume of ∼3 mm radius to distinguish malignant breast lesions in prospectively and consecutively collected tumoral and non-tumoral ex-vivo breast tissue samples from 91 patients. We characterized the dielectric properties of 346 sites in these samples, encompassing malignant, fibrocystic disease and normal breast tissues. An expert pathologist subsequently evaluated all measurement sites. ResultsAt multivariate analysis, mm-wave dielectric properties were significantly correlated to histologic diagnosis and fat content. Further, using 5-fold cross-validation in a Bayesian logistic mixed model that considered the patient as a random effect, the mm-wave dielectric properties of neoplastic tissues were significantly different from normal breast tissues, but not from fibrocystic tissue. ConclusionReliable discrimination of malignant from normal, fat-rich breast tissue to a depth compatible with surgical margin assessment requirements was achieved with mm-wave spectroscopy.

Dielectric Properties Characterization From 0.5 to 50 GHz of Breast Cancer Tissues

Knowledge of the dielectric properties of human tissues is important for several biomedical applications, including imaging and hyperthermia treatment, as well as for determining safety thresholds in policy making. Breast tissues, both normal and tumorous, are of particular interest because of the medical and social impact of breast cancers. While experimental data is available up to 20 GHz, for higher frequencies, this information is missing, or has been extrapolated from models based on lower-frequency data. Emerging technologies and applications in the millimeter-wave region would benefit from experimental data that bridge this gap. This paper presents the characterization of dielectric properties of breast tissues for the frequency range from 0.5 to 50 GHz. Cole–Cole models are derived for normal and tumorous tissues based on experimental measurements on more than 220 tissue samples obtained at surgery ( ex vivo ) from a population exceeding 50 patients, covering a wide span of normal and tumorous tissues, from patients ranging in age from 28 to 85 years, with a time from excision to measurements under 3.5 h. This paper also presents a comprehensive analysis of the differences between normal and tumorous breast tissues at different frequencies in terms of sensitivity and specificity.

A Feasible Novel Technique for Breast Cancer Imaging Using UWB-Microwave Antennas

Microwave Imaging (MI) of breast cancer is an emerging non-invasive and non-ionizing technique for breast cancer diagnosis based on microwave radiation backscattered by breast tissues. Usually, MBI explore dielectric properties of breast tissues to increase the imaging contrast between tumor and healthy tissue through an Inverse Image Reconstruction Algorithm. Furthermore, MBI systems could be cost-effectively, compact and recent developments drive them to wearable soon. Even X-ray Mammography is the gold-standard for imaging tumors inside breast; it still is low contrast for early diagnostic, painful and age- and dose-restricted because ionizing radiation. Then, in long-term, our group is motivated to develop MBI technique and cost-effectively wearable systems for in vivo early diagnosis of breast cancer as a complimentary to X-ray Mammography. In short-term, we had been designing our systems by simulations, manufacturing and initial in vitro tests in lab. This work presents initial results of design and simulation of a system based on hard and/or flexible antennas ranging between 0.001 GHz to 3 GHz for in vitro experimentation. In detail, two different shapes (rectangular patch and circular slot) of Micro strip Patch antennas were designed and simulated in FR4, Cotton, Polyester and Pyralux Polyimide (for Flexible antennas) materials. The resonance frequency of antennas depends on permittivity of substrate material and its geometry, so the High Frequency Simulation Software (HFSS) simulated scattering parameters of designed antennas, which were also tested on mimic-phantoms of breast. The simulation of rectangular patch and bow-tie antennas resulted on a like-Gaussian curve of microwave emission / detection peaked at 1.9-2.7 GHz with ~50-90MHz band width.

Experimental feasibility of multistatic holography for breast microwave radar image reconstruction.

The goal of this study was to assess the experimental feasibility of circular multistatic holography, a novel breast microwave radar reconstruction approach, using experimental datasets recorded using a preclinical experimental setup. The performance of this approach was quantitatively evaluated by calculating the signal to clutter ratio (SCR), contrast to clutter ratio (CCR), tumor to fibroglandular response ratio (TFRR), spatial accuracy, and reconstruction time. Five datasets were recorded using synthetic phantoms with the dielectric properties of breast tissue in the 1-6 GHz range using a custom radar system developed by the authors. The datasets contained synthetic structures that mimic the dielectric properties of fibroglandular breast tissues. Four of these datasets the authors covered an 8 mm inclusion that emulated a tumor. A custom microwave radar system developed at the University of Manitoba was used to record the radar responses from the phantoms. The datasets were reconstructed using the proposed multistatic approach as well as with a monostatic holography approach that has been previously shown to yield the images with the highest contrast and focal quality. For all reconstructions, the location of the synthetic tumors in the experimental setup was consistent with the position in the both the monostatic and multistatic reconstructed images. The average spatial error was less than 4 mm, which is half the spatial resolution of the data acquisition system. The average SCR, CCR, and TFRR of the images reconstructed with the multistatic approach were 15.0, 9.4, and 10.0 dB, respectively. In comparison, monostatic images obtained using the datasets from the same experimental setups yielded average SCR, CCR, and TFRR values of 12.8, 4.9, and 5.9 dB. No artifacts, defined as responses generated by the reconstruction method of at least half the energy of the tumor signatures, were noted in the multistatic reconstructions. The average execution time of the images formed using the proposed approach was 4 s, which is one order of magnitude faster than the current state-of-the-art time-domain multistatic breast microwave radar reconstruction algorithms. The images generated by the proposed method show that multistatic holography is capable of forming spatially accurate images in real-time with signal to clutter levels and contrast values higher than other published monostatic and multistatic cylindrical radar reconstruction approaches. In comparison to the monostatic holographic approach, the images generated by the proposed multistatic approach had SCR values that were at least 50% higher. The multistatic images had CCR and TFRR values at least 200% greater than those formed using a monostatic approach.

Sensitivity of the Distorted Born Iterative Method to the Initial Guess in Microwave Breast Imaging

The distorted Born iterative method (DBIM) has been explored recently for microwave breast imaging. DBIM is an iterative method; thus, it requires an initial guess of the dielectric properties of the breast. In this paper, we study the sensitivity of DBIM imaging accuracy and convergence speed to the properties of a homogeneous initial guess. We conduct this investigation for a multifrequency formulation of DBIM, wherein the dispersive breast tissue properties are described with a Debye model. The parameters of the Debye model for the initial guess are linearly linked to reflect typical breast tissue dielectric properties. The static permittivity characterizing the properties is swept over an appropriate range of initial guesses and DBIM is used to obtain imaging results for each guess. Image quality and the number of iterations required for convergence is evaluated using three-dimensional (3-D) anatomically realistic numerical breast phantoms. This investigation not only vividly illustrates the sensitivity of DBIM to the initial guess but also definitively demonstrates that the use of initial values close to the average properties of the breast yields near-optimal performance. Finally, we present and evaluate a practical algorithm for estimating the average properties to be used as the initial guess.

Average dielectric property analysis of complex breast tissue with microwave transmission measurements.

Prior information about the average dielectric properties of breast tissue can be implemented in microwave breast imaging techniques to improve the results. Rapidly providing this information relies on acquiring a limited number of measurements and processing these measurement with efficient algorithms. Previously, systems were developed to measure the transmission of microwave signals through breast tissue, and simplifications were applied to estimate the average properties. These methods provided reasonable estimates, but they were sensitive to multipath. In this paper, a new technique to analyze the average properties of breast tissues while addressing multipath is presented. Three steps are used to process transmission measurements. First, the effects of multipath were removed. In cases where multipath is present, multiple peaks were observed in the time domain. A Tukey window was used to time-gate a single peak and, therefore, select a single path through the breast. Second, the antenna response was deconvolved from the transmission coefficient to isolate the response from the tissue in the breast interior. The antenna response was determined through simulations. Finally, the complex permittivity was estimated using an iterative approach. This technique was validated using simulated and physical homogeneous breast models and tested with results taken from a recent patient study.

Breast cancer detection using interferometric MUSIC: experimental and numerical assessment.

In microwave breast cancer detection, it is often beneficial to arrange sensors in close proximity to the breast. The resultant coupling generally changes the antenna response. As an a priori characterization of the radio frequency system becomes difficult, this can lead to severe degradation of the detection efficacy. The purpose of this paper is to demonstrate the advantages of adopting an interferometric multiple signal classification (I-MUSIC) approach due to its limited dependence from a priori information on the antenna. The performance of I-MUSIC detection was measured in terms of signal-to-clutter ratio (SCR), signal-to-mean ratio (SMR), and spatial displacement (SD) and compared to other common linear noncoherent imaging methods, such as migration and the standard wideband MUSIC (WB-MUSIC) which also works when the antenna is not accounted for. The data were acquired by scanning a synthetic oil-in-gelatin phantom that mimics the dielectric properties of breast tissues across the spectrum 1-3 GHz using a proprietary breast microwave multi-monostatic radar system. The phantom is a multilayer structure that includes skin, adipose, fibroconnective, fibroglandular, and tumor tissue with an adipose component accounting for 60% of the whole structure. The detected tumor has a diameter of 5 mm and is inserted inside a fibroglandular region with a permittivity contrast εr-tumor/εr-fibroglandular < 1.5 over the operating band. Three datasets were recorded corresponding to three antennas with different coupling mechanisms. This was done to assess the independence of the I-MUSIC method from antenna characterizations. The datasets were processed by using I-MUSIC, noncoherent migration, and wideband MUSIC under equivalent conditions (i.e., operative bandwidth, frequency samples, and scanning positions). SCR, SMR, and SD figures were measured from all reconstructed images. In order to benchmark experimental results, numerical simulations of equivalent scenarios were carried out by using CST Microwave Studio. The three numerical datasets were then processed following the same procedure that was designed for the experimental case. Detection results are presented for both experimental and numerical phantoms, and higher performance of the I-MUSIC method in comparison with the WB-MUSIC and noncoherent migration is achieved. This finding is confirmed for the three different antennas in this study. Although a delocalization effect occurs, experimental datasets show that the signal-to-clutter ratio and the signal-to-mean performance with the I-MUSIC are at least 5 and 2.3 times better than the other methods, respectively. The numerical datasets calculated on an equivalent phantom for cross-testing confirm the improved performance of the I-MUSIC in terms of SCR and SMR. In numerical simulations, the delocalization effect is dramatically reduced up to an SD value of 1.61 achieved with the I-MUSIC in combination with the antipodal Vivaldi antenna. This shows that mechanical uncertainties are the main reason for the delocalization effect in the measurements. Experimental results show that the I-MUSIC generates images with signal-to-clutter levels higher than 5.46 dB across all working conditions and it reaches 7.84 dB in combination with the antipodal Vivaldi antenna. Numerical simulations confirm this trend and due to ideal mechanical conditions return a signal-to-clutter level higher than 7.61 dB. The I-MUSIC largely outperforms the methods under comparison and is able to detect a 5-mm tumor with a permittivity contrast of 1.5.

Biocompatible Implanted Dielectric Sensors for Breast Cancer Detection

This article describes the development of a method for a biocompatible sensor device for the intent of in-vivo breast tissue dielectric properties measurements. This article focuses on a specific type of sensor that utilizes an LC circuit with an inter-digital capacitor (IDC) with small size and high sensitivity for early stage breast cancer detection. To meet this objective an IDC was optimized in terms of contrast and miniaturized size via simulation techniques. For experimental testing, a scaled-up prototype inter-digital capacitor and spiral square inductor sensor was fabricated, and tested with known media, such as distilled water and glycerol. The results suggest that there is a need for further development, such as fabrication and testing for the biocompatible, miniaturized sensor for breast tissue application.

INVESTIGATION OF CLASSIFIERS FOR TUMOR DETECTION WITH AN EXPERIMENTAL TIME-DOMAIN BREAST SCREENING SYSTEM

In this work we examine, for the flrst time, the use of classiflcation algorithms for early- stage tumor detection with an experimental time-domain microwave breast screening system. The experimental system contains a 16-element antenna array, and testing is done on breast phantoms that mimic breast tissue dielectric properties. We obtain experimental data from multiple breast phantoms with two possible tumor locations. In this work, we investigate a method for detecting the tumors within the breast but without the usual complexity inherent to image-generation methods, and conflrm its feasibility on experimental data. The proposed method uses machine learning techniques, namely Support Vector Machines (SVM) and Linear Discriminant Analysis (LDA), to determine whether the current breast being scanned is tumor-free. Our results show that both SVM and LDA methods have promise as algorithms supporting early breast cancer microwave screening.