This article outlines the main features of active, passive, and hybrid systems under investigation for breast cancer detection. Our main focus is on active microwave systems, in particular microwave tomography and confocal microwave imaging.

Enhancing breast tumor detection with near-field imaging

Microwaves and millimeter waves have been used extensively to image dielectric bodies. The application of microwaves in biomedical imaging and diagnostics, however, remains a field with many uncharted territories. This article is an overview on medical imaging using microwave imaging for breast cancer and its challenges, hopes, and outlook.

Microwave Imaging for Breast Cancer

The authors propose a spatial iterative algorithm for electromagnetic imaging based on a Newton-Kantorovich procedure for the reconstruction of the complex permittivity of inhomogeneous lossy dielectric objects with arbitrary shape. Starting from integral representation of the electric field and using the moment method, this technique has been developed for 2-D (for TM and TE polarization cases) objects as well as for 3-D objects. Its performance has been compared with spectral techniques of classical diffraction tomography, the modified Newton method, and the pseudo-inverse method. >

Inverse scattering: an iterative numerical method for electromagnetic imaging

Surveys the different types of microwave sensors and reviews the latest developments reported by European institutes and companies. Attention is given to resonator, transmission, reflection, radar, and radiometer sensors, and to active imaging. >

Industrial microwave sensors

Microwave breast imaging (using electromagnetic waves of frequencies around 1 GHz) has mostly remained at the research level for the past decade, gaining little clinical acceptance. The major hurdles limiting patient use are both at the hardware level (challenges in collecting accurate and noncorrupted data) and software level (often plagued by unrealistic reconstruction times in the tens of hours). In this paper we report improvements that address both issues. First, the hardware is able to measure signals down to levels compatible with sub-centimeter image resolution while keeping an exam time under 2 min. Second, the software overcomes the enormous time burden and produces similarly accurate images in less than 20 min. The combination of the new hardware and software allows us to produce and report here the first clinical 3-D microwave tomographic images of the breast. Two clinical examples are selected out of 400+ exams conducted at the Dartmouth Hitchcock Medical Center (Lebanon, NH). The first example demonstrates the potential usefulness of our system for breast cancer screening while the second example focuses on therapy monitoring.

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Fast 3-D Tomographic Microwave Imaging for Breast Cancer Detection

A numerical method and experimental technique for microwave imaging of inhomogenous bodies is presented. This method is based on the interpretation of the diffraction phenomena and leads to tomographic reconstruction of the body under investigation. Various numerical examples are given on spatial impulse response, recognition of dielectric rods, inhomogeneous bodies, and simulated human arm. Different experimental results on dielectric rods and isolated animal organs are also given.

/pdf/active-microwave-imaging-of-inhomogeneous-bodies-1kdal66kx1.pdf

Active microwave imaging of inhomogeneous bodies

This paper deals with numerical processing techniques and practical applications of active microwave imaging. Different wavefront processing are presented, from an immediate use of measured projections to more complex procedures. Both spectral approaches to diffraction tomography and spatial iterative methods for generalized imaging are considered using multi-incidence of multifrequency techniques for 3D and/or 2D objects. The technology of the so-called microwave camera is presented for the fast recording of the scattered field with arrays of probes involving one- or two-dimensional sensors at a single frequency or in a broad-frequency band. Three different systems are depicted: a single-frequency linear sensor devoted to industrial applications (on-line transverse control of conveyed products), a single-frequency planar microwave camera for biomedical applications and research, and a broad-frequency linear microwave camera for civil engineering applications (detection of the rebars in reinforced concrete strctures). Microwave images obtained experimentally with the three systems are presented on configurations of practical interest for each field of application.

Microwave tomography: From theory to practical imaging systems

Key results are summarized of efforts to significantly reduce the near-field measurement time by utilizing one- or two-dimensional arrays of modulated scattering probes in lieu of the single probe ordinarily used in conventional near-field measurement techniques. Results of analytical, numerical, and experimental investigations show that the modulated-scattering technique (MST) using arrays of hundreds or even thousands of modulated scattering probes can be used to map the complex near-field of antennas or scatterers in a few seconds or minutes. The results also strongly indicate that classical (nonmodulated) receiving/transmitting arrays can be adapted for rapid near-field data collection. Major factors affecting the accuracy and speed of probe arrays for near-field measurement are delineated and discussed. Experimental results obtained using laboratory prototype MST systems are also presented and discussed. >

/pdf/rapid-near-field-antenna-testing-via-arrays-of-modulated-46jkgpv4cp.pdf

Rapid near-field antenna testing via arrays of modulated scattering probes

Many diagnostic techniques in geophysics and civil engineering are based on the interaction of electromagnetic waves with objects buried in homogeneous or stratified media. Most of the investigations are concerned with the detection of buried objects, but a few papers have dealt with the problem of identifying the objects. The proposed method is based on the integral representation for a plane wave incident on a lossy half-space containing a cylindrical object of arbitrary cross section and electrical properties. The induced current distribution in the object is obtained from the backscattered field measurement in amplitude and phase. In order to improve the spatial resolution of the image, the scattered field is measured for different plane wave incidence and frequencies. Results of numerical simulations concerning the shape and size of the object for different values of soil electromagnetic parameters are presented in this paper.

Electromagnetic Modeling for Microwave Imaging of Cylindrical Buried Inhomogeneities

Recent results have demonstrated the feasibility of quasi-real-time, active as well as harmless microwave imaging for biomedical purposes. Such a process allows tomographic reconstructions based on differences in the complex permittivity of tissues, the temperature dependence of which can be used for remote thermal sensing. A basic experiment conducted in water at 3-GHz yielded information on spatial resolution and temperature sensitivity. Discussion is devoted to potential capabilities and limitations of this remote-sensing approach in more complicated situations.

/pdf/on-the-possible-use-of-microwave-active-imaging-for-remote-4idb3s2fhs.pdf

Jean-Charles Bolomey

Papers

Active microwave imaging of inhomogeneous bodies

Microwave tomography: From theory to practical imaging systems

Rapid near-field antenna testing via arrays of modulated scattering probes

Electromagnetic Modeling for Microwave Imaging of Cylindrical Buried Inhomogeneities

On the Possible Use of Microwave-Active Imaging for Remote Thermal Sensing