Milica Popović

Time-Domain Multistatic Radar System for Microwave Breast Screening

This letter presents an experimental system for microwave breast cancer detection that uses multistatic radar. The system operates by transmitting a short-duration pulse and collecting the signals scattered within the breast. We describe the 16-element array, along with the pulse generation scheme, switches, and all auxiliary equipment. This work provides a sample selection of the collected time-domain data and shows the proof of concept by imaging the breast tumors in realistically shaped breast phantoms.

A Novel Ultra-Compact Broadband Antenna for Microwave Breast Tumor Detection

This paper presents a novel resistively loaded antenna design for microwave breast cancer detection. The antenna is planar and ultra-compact,and can be easily manufactured using PCB technology with embedded thin-film resistive layers. Through numerical simulations,the antenna demonstrates a return loss below −10 dB over a wide frequency range from 2 to 35 GHz. For pulse radiation in the ultra-wideband (UWB) range in a biological medium, the antenna shows an excellent fidelity above 0.95 and a relatively high radiation efficiency of 39.21% in comparison to resistively loaded antennas. In addition,a design rule guideline is presented for designing the antenna to radiate in a specific background medium and with a given lower operating frequency. Finally,a complete microstrip feed design is presented for the antenna operating in the UWB range.

An Early Clinical Study of Time-Domain Microwave Radar for Breast Health Monitoring

This study reports on monthly scans of healthy patient volunteers with the clinical prototype of a microwave imaging system. The system uses time-domain measurements, and incorporates a multistatic radar approach to imaging. It operates in the 2-4 GHz range and contains 16 wideband sensors embedded in a hemispherical dielectric radome. The system has been previously tested on tissue phantoms in controlled experiments. With this system prototype, we scanned 13 patients (26 breasts) over an eight-month period, collecting a total of 342 breast scans. The goal of the study described in this paper was to investigate how the system measurements are impacted by multiple factors that are unavoidable in monthly monitoring of human subjects. These factors include both biological variability (e.g., tissue variations due to hormonal changes or weight gain) and measurement variability (e.g., inconsistencies in patient positioning, system noise). For each patient breast, we process the results of the monthly scans to assess the variability in both the raw measured signals and in the generated images. The significance of this study is that it quantifies how much variability should be anticipated when conducting microwave breast imaging of a healthy patient over a longer period. This is an important step toward establishing the feasibility of the microwave radar imaging system for frequent monitoring of breast health.

Flexible 16 Antenna Array for Microwave Breast Cancer Detection

Radar-based microwave imaging has been widely studied for breast cancer detection in recent times. Sensing dielectric property differences of tissues has been studied over a wide frequency band for this application. We design single- and dual-polarization antennas for wireless ultrawideband breast cancer detection systems using an inhomogeneous multilayer model of the human breast. Antennas made from flexible materials are more easily adapted to wearable applications. Miniaturized flexible monopole and spiral antennas on a 50-μm Kapton polyimide are designed, using a high-frequency structure simulator, to be in contact with biological breast tissues. The proposed antennas are designed to operate in a frequency range of 2-4 GHz (with reflection coefficient (S11) below -10 dB). Measurements show that the flexible antennas have good impedance matching when in different positions with different curvature around the breast. Our miniaturized flexible antennas are 20 mm × 20 mm. Furthermore, two flexible conformal 4 × 4 ultrawideband antenna arrays (single and dual polarization), in a format similar to that of a bra, were developed for a radar-based breast cancer detection system. By using a reflector for the arrays, the penetration of the propagated electromagnetic waves from the antennas into the breast can be improved by factors of 3.3 and 2.6, respectively.

Experimental Demonstration of Pulse Shaping for Time-Domain Microwave Breast Imaging

We experimentally demonstrate a low-cost hardware technique for synthesizing a speciflc electromagnetic pulse shape to improve a time-domain microwave breast imaging system. A synthesized broadband re∞ector (SBR) fllter structure is used to reshape a generic impulse to create an ad-hoc pulse with a speciflcally chosen frequency spectrum that improves the detection and imaging capabilities of our experimental system. The tailored pulse shape beneflts the system by improving the level of signal detection after transmission through the breast and thus permits higher-resolution images. We report on our ability to use this technique to detect the presence of tumours in realistic breast phantoms composed of varying quantities of glandular tissue. Additionally, we provide a set of images based on this experimental data that demonstrates the increased efiectiveness of the system using the SBR-shaped pulse in the localisation and identiflcation of the embedded tumour.

Finite element modeling of electromagnetic signal propagation in a phantom arm

Improving the control of artificial arms remains a considerable challenge. It may be possible to graft remaining peripheral nerves in an amputated limb to spare muscles in or near the residual limb and use these nerve-muscle grafts as additional myoelectric control signals. This would allow simultaneous control of multiple degrees of freedom (DOF) and could greatly improve the control of artificial limbs. For this technique to be successful, the electromyography (EMG) signals from the nerve-muscle grafts would need to be independent of each other with minimal crosstalk. To study EMG signal propagation and quantify crosstalk, finite element (FE) models were developed in a phantom-arm model. The models were validated with experimental data collected by applying sinusoidal excitations to a phantom-arm model and recording the surface electric potential distribution. There was a very high correlation (r>0.99) between the FEM data and the experimental data, with the error in signal magnitude generally less than 5%. Simulations were then performed using muscle dielectric properties with static, complex, and full electromagnetic solvers. The results indicate that significant displacement currents can develop (>50% of total current) and that the fall-off of surface signal power varies with how the signal source is modeled.

Spectral Difference Between Microwave Radar and Microwave-Induced Thermoacoustic Signals

This letter presents a spectral content comparison of the signals generated in the microwave radar (MR) and microwave-induced thermoacoustic (MIT) imaging systems. Two physical processes occur when microwave interacts with a lossy dielectric object. First, due to the contrast in the complex permittivity between the embedded object and background medium, reflection of microwave energy occurs at the interface. Second, due to the contrast in the absorption coefficient between the object and background medium and the consequent thermal expansion, microwave induces an acoustic wave. As a method of comparison between the inputs and outputs of the MR and MIT processes, we define the MR and MIT channels. We use a two-dimensional (2-D) example to demonstrate that the MR channel over the ultrawideband (UWB) spectrum from 3.1 to 10.6 GHz manifests different fading from the MIT channel over the ultrasonic spectrum from 0.32 to 1.10 MHz. The two output signals are distinctive, but they are co-registered to the same object. Hence, using the information provided by both could enhance the imaging modality. We apply this dual-physics scheme in the context of breast tumor detection.

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.

Microwave Radar and Microwave-Induced Thermoacoustics: Dual-Modality Approach for Breast Cancer Detection

Microwave radar and microwave-induced thermoacoustics, recently proposed as promising breast cancer detection techniques, each have shortcomings that reduce detection performance. Making the assumption that the measurement noises experienced when applying these two techniques are independent, we propose a methodology to process the input signals jointly based on a hypothesis testing framework. We present two test statistics and derive their distributions to set the thresholds. The methodology is evaluated on numerically simulated signals acquired from 2-D numerical breast models using finite-difference time-domain method. Our results show that the proposed dual-modality approach can give a significant improvement in detection performance.

A Time-Domain Microwave System for Breast Cancer Detection Using a Flexible Circuit Board

We present the design of a flexible multilayer circuit board for use in a custom-built microwave system for breast health monitoring. The flexible circuit features both an integrated solid-state switching network and 16 wideband antennas, which transmit short-duration pulses into the breast tissues and receive the backscattered responses. By integrating the switching matrix and the antenna array on the same substrate, we reduce the overall cost and size of the system in comparison with previously demonstrated systems in the literature. We characterize the performance of the flexible circuit board using our clinically tested experimental system and demonstrate its functionality through successful imaging of dielectrically realistic breast phantoms that simulate the presence of a tumor. This represents a step toward a more patient-friendly, compact, cost-effective, and wearable design in contrast to previous systems in the literature that required a clinical table or used bulky rigid antenna housings and electromechanical switching networks.