Jeremie Bourqui

Balanced Antipodal Vivaldi Antenna With Dielectric Director for Near-Field Microwave Imaging

A balanced antipodal Vivaldi antenna is designed to be used as a sensor for a microwave breast cancer detection system. The antenna has the ability to send short electromagnetic pulses into the near-field, with low distortion, low loss and in a directional manner. The antenna directivity is further improved by the inclusion of a novel feature in the antenna aperture called a “director” which consists of a profiled piece of higher dielectric constant material. Several simulated results are successfully confirmed with measurements. Reflections of a tumor placed in a breast model are simulated for two cases, namely a balanced antipodal Vivaldi antenna with and without a director. Greater tumor responses are recorded with the director present, demonstrating the potential of this feature for microwave breast imaging.

Microwave Breast Imaging With a Monostatic Radar-Based System: A Study of Application to Patients

A prototype microwave breast imaging system is used to scan a small group of patients. The prototype implements a monostatic radar-based approach to microwave imaging and utilizes ultra-wideband signals. Eight patients were successfully scanned, and several of the resulting images show responses consistent with the clinical patient histories. These encouraging results motivate further studies of microwave imaging for breast health assessment.

A prototype system for measuring microwave frequency reflections from the breast

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.

Measurement and analysis of microwave frequency signals transmitted through the breast

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.

Laser Surface Estimation for Microwave Breast Imaging Systems

Microwave breast imaging techniques involve collecting measurements from a breast that is positioned in a scanner. While the patient interface typically includes a hole through which the breast is placed when the patient lies in the prone position, the exact location and shape of breast are not known. In this paper, we explore the addition of a laser sensor and associated algorithms in order to provide a rapid and accurate estimate of the breast surface location. We demonstrate that the laser is capable of estimating surfaces with improved accuracy compared to microwave measurements. The impact of accurate surface estimation on images is shown, and results obtained from human scans are presented.

Shielded UWB Sensor for Biomedical Applications

A new ultrawideband (UWB) sensor for microwave imaging and sensing is introduced. The structure consists of a dielectric loaded Vivaldi radiating element encapsulated into a cylindrical waveguide. Its length and diameter are 95 and 25.4 mm, respectively. Electromagnetic energy is coupled into the human body by direct contact between the aperture and skin, while the rest of the sensor structure is fully shielded. The sensor shows ability to transmit and receive electromagnetic energy from 1.8 to 12 GHz.

Evaluation of 3-D Acquisition Surfaces for Radar-Based Microwave Breast Imaging

This study investigates the impact that the acquisition surface has on the internal coverage of an object in the context of radar-based near-field microwave (MW) breast imaging. We define an acquisition surface as the surface over, which data are collected. Three different three-dimensional (3-D) data acquisition surfaces are investigated: 1) cylindrical, 2) hemispherical, and 3) patient specific. Three 3-D numerical breast models are used for the study. A realistic ultra-wideband (UWB) antenna generates incident fields and records the total fields. The responses from targets are analyzed, and object coverage is evaluated in terms of range distances, cross-range distances, and cumulative radiated power directed into the object by the antenna array embedded in the acquisition surface. Images are formed to verify these observations. We demonstrate that a patient-specific acquisition surface provides greater responses from targets, superior object coverage and improved images compared to the other acquisition surfaces studied.

Antenna Evaluation for Ultra-Wideband Microwave Imaging

Numerous antenna designs have been proposed for microwave breast imaging utilizing an ultra-wideband frequency range. The antennas are typically compact, operate in an immersion medium, and have a band covering at least 2–10 GHz. We have developed 3 antennas for our UWB microwave breast imaging system. In this contribution, we compare the performance of the antennas in order to gain insight into the relationship between antenna performance metrics and image quality.

System for Bulk Dielectric Permittivity Estimation of Breast Tissues at Microwave Frequencies

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%.

Safety assessment of ultra-wideband antennas for microwave breast imaging

This article deals with the safety assessment of several ultra-wideband (UWB) antenna designs for use in prototype microwave breast imaging systems. First, the performances of the antennas are validated by comparison of measured and simulated data collected for a simple test case. An efficient approach to estimating the specific energy absorption (SA) is introduced and validated. Next, SA produced by the UWB antennas inside more realistic breast models is computed. In particular, the power levels and pulse repetition periods adopted for the SA evaluation follow the measurement protocol employed by a tissue sensing adaptive radar (TSAR) prototype system. Results indicate that the SA for the antennas examined is below limits prescribed in standards for exposure of the general population; however, the difficulties inherent in applying such standards to UWB exposures are discussed. The results also suggest that effective tools for the rapid evaluation of new sensors have been developed.