Microwave imaging of the breast is of interest for monitoring breast health, and approaches to active microwave imaging include tomography and radar-based methods. While the literature contains a growing body of work related to microwave breast imaging, there are only a few prototype systems that have been used to collect data from humans. In this paper, a prototype system for monostatic radar-based imaging that has been used in an initial study measuring reflections from volunteers is discussed. The performance of the system is explored by examining the mechanical positioning of sensor, as well as microwave measurement sensitivity. To gain insight into the measurement of reflected signals, simulations and measurements of a simple phantom are compared and discussed in relation to system sensitivity. Finally, a successful scan of a volunteer is described.

This paper presents an apparatus capable of measuring the average dielectric properties of the human breast. It is composed of two arrays between which the breast is placed. Each array is fitted with five ultra-wideband (UWB) sensors operating from 1.5 to 10 GHz. Direct contact is made between the breast skin and the sensor arrays, avoiding any matching liquid. The transmission coefficients for all possible sensor pairs in the two arrays are measured in 15 s. The data are then transformed to the time domain, and a time delay spectroscopy technique is used to estimate permittivity. The system was tested using phantoms with known properties and showed accurate estimations. Tests on human subjects resulted in dielectric property estimates in line with published data, while variation between scans of the same volunteer is as small as 2%.

Microwave approaches to breast imaging include the measurement of signals transmitted through and reflected from the breast. Prototype systems typically feature sensors separated from the breast, resulting in measurements that include the effects of the environment and system. To gain insight into transmission of microwave signals through the breast, a system that places sensors in direct contact with the breast is proposed. The system also includes a lossy immersion medium that enables measurement of the signal passing through the breast while significantly attenuating signals traveling along other paths. Collecting measurements at different separations between sensors also provides the opportunity to estimate the average electrical properties of the breast tissues. After validation through simulations and measurements, a study of 10 volunteers was performed. Results indicate symmetry between the right and left breast and demonstrate differences in attenuation, maximum frequency for reliable measurement, and average properties that likely relate to variations in breast composition.

Biomedical imaging and sensing applications in many scenarios demand accurate surface estimation from a sparse set of noisy measurements. These measurements may arise from a variety of sensing modalities, including laser or electromagnetic samples of an object’s surface. We describe a state-of-the-art microwave imaging prototype that has sensors to acquire both microwave and laser measurements. The approach developed to translate sparse samples of the breast surface into an accurate estimate of the region of interest is detailed. To evaluate the efficacy of the method, laser and electromagnetic samples are acquired by sensors from three realistic breast models with varying sizes and shapes. A set of metrics is developed to assist with the investigation and demonstrate that the algorithm is able to accurately estimate the shape of a realistic breast phantom when only a sparse set of data are available. Moreover, the algorithm is robust to the presence of measurement noise, and is effective when applied to measurement scans of patients acquired with the prototype.

A second-generation monostatic radar system to measure microwave reflections from the human breast is presented and analyzed. The present system can measure the outline of the breast with an accuracy of ±1 mm and precisely place the microwave sensor in an adaptive matter such that microwaves are normally incident on the skin. Microwave reflections are measured between 10 MHz to 12 GHz with sensitivity of 65 to 75 dB below the input power and a total scan time of 30 min for 140 locations. The time domain reflections measured from a volunteer show fidelity above 0.98 for signals in a single scan. Finally, multiple scans of a breast phantoms demonstrate the consistency of the system in terms of recorded reflection, outline measurement, and image reconstruction.

Microwave imaging has been proposed for breast cancer detection and treatment monitoring. Prototype systems based on tomography and radar-based techniques have been tested on human subjects with promising results. Previously, we developed a system that estimated average permittivity in regions of the breast using signals transmitted through the tissues. Encouraging results with volunteers and patients motivated development of a system capable of creating more detailed images of the entire breast. Objective: In this paper, we aim to assess the performance of this next generation microwave imaging system and demonstrate scans of human subjects that relate to clinical information. Methods: With a novel imaging system, scans of homogeneous phantoms and phantoms with inclusions of various sizes are collected. The accuracy, detection and localization are assessed. A pilot study is carried out with a small group of volunteers with previous mammograms. Results: Images of flexible phantoms have average error of less than 10 % in the reconstructed average permittivity. Detection of inclusions of 1 cm diameter and greater is demonstrated. The feasibility of scanning human subjects is also demonstrated by providing microwave images of several healthy volunteers with previous mammograms. Significance: A novel high-resolution microwave transmission imaging system, in conjunction with a fast quantitative reconstruction algorithm capable of detecting 1 cm diameter inclusions, is designed for breast imaging applications. It can image various breast sizes without the need for matching fluid. Conclusion: Overall, the results indicate that this imaging system is well suited for further exploration of microwave imaging with human subjects.