Maria A. Stuchly

Confocal microwave imaging for breast cancer detection: localization of tumors in three dimensions

The physical basis for breast tumor detection with microwave imaging is the contrast in dielectric properties of normal and malignant breast tissues. Confocal microwave imaging involves illuminating the breast with an ultra-wideband pulse from a number of antenna locations, then synthetically focusing reflections from the breast. The detection of malignant tumors is achieved by the coherent addition of returns from these strongly scattering objects. In this paper, we demonstrate the feasibility of detecting and localizing small (<1 cm) tumors in three dimensions with numerical models of two system configurations involving synthetic cylindrical and planar antenna arrays. Image formation algorithms are developed to enhance tumor responses and reduce early- and late-time clutter. The early-time clutter consists of the incident pulse and reflections from the skin, while the late-time clutter is primarily due to the heterogeneity of breast tissue. Successful detection of 6-mm-diameter spherical tumors is achieved with both planar and cylindrical systems, and similar performance measures are obtained. The influences of the synthetic array size and position relative to the tumor are also explored.

Enhancing breast tumor detection with near-field imaging

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.

Coaxial Line Reflection Methods for Measuring Dielectric Properties of Biological Substances at Radio and Microwave Frequencies-A Review

Coaxial line reflection methods for measuring dielectric properties of biological materials at radio (RF) and microwave (MF) frequencies are reviewed and compared from the point of view of their relative uncertainties of measurement of lossy substances with high dielectric constant. Advantages and limitations of different methods and some practical recommendations are presented.

A study of the handset antenna and human body interaction

The antenna radiation pattern and other characteristics are significantly altered by the presence of the human body. This interaction as well as the resultant deposition of microwave power in the body (specific absorption rate-SAR) are of particular interest for cellular telephones and similar communication devices. This paper builds on and extends the previous analyses of parameters that influence the antenna-user interaction. Computer tomography (CT) and magnetic resonance imaging (MRI)-derived, high-resolution models of the human head are used. The numerical analysis is performed with the finite-difference time-domain (FDTD) method. The specific findings are: 1) a box model of a human head provides grossly distorted and unreliable results for the antenna radiation pattern; 2) a spherical model of the human head provides results that are relatively close to those obtained with a relatively simple, but more realistic, head model; 3) the SAR values obtained with spherical or simplified head models, that do not include the ear, are greater than those for a realistic head model that includes the ear; and 4) a hand holding the handset absorbs significant amount of antenna output power, which can be considerably decreased by modifying the geometry of the handset metal box.

Measurement of Radio Frequency Permittivity of Biological Tissues with an Open-Ended Coaxial Line: Part I

An open-ended coaxial line is analyzed as a sensor for in vivo measurement of the complex permittivity of biological substances. The measurement system, based on two computerized network analyzers operating at frequencies from 10 MHz to 1 GHz, is described. Experimental results are presented in a companion paper.

Microwave detection of breast cancer

Breast cancer affects many women, and early detection aids in fast and effective treatment. Mammography, which is currently the most popular method of breast screening, has some limitations, and microwave imaging offers an attractive alternative. A microwave system for breast tumor detection that uses previously introduced confocal microwave imaging techniques is presented in this paper. The breast is illuminated with an ultrawide-band pulse and a synthetic scan of the focal point is used to detect tumors; however, the geometric configuration and algorithms are different from those previously used. The feasibility of using small antennas for tumor detection is investigated. Signal processing algorithms developed to mitigate the dominant reflection from the skin are described, and the effectiveness of these skin subtraction algorithms is demonstrated. Images of homogeneous and heterogeneous breast models are reconstructed with various numbers of antennas. Both the influence of antenna spacing and the suitability of simplified models for system evaluation are examined.

Three-dimensional subgridding algorithm for FDTD

In many computational problems solved using the finite-difference time-domain (FDTD) technique, there is a need to model selected volumes with higher resolution than the whole computational space. An efficient algorithm has been developed for this purpose that provides the mesh refinement by the factor of two in each direction. The algorithm can be used in two-dimensional (2-D) and three-dimensional (3-D) problems and provides for subgridding in both space and time. Performance of the 3-D algorithm was tested in waveguides and resonators. A high accuracy and efficiency were observed in all test cases with insignificant (of an order of -60 dB) reflections from mesh interfaces. Practical applications of the algorithm in the analyses of a resonator with a dielectric rod and of a cellular phone behavior in the vicinity of the operator head are also reported.

Measurement of Radio Frequency Permittivity of Biological Tissues with an Open-Ended Coaxial Line: Part II - Experimental Results

The permittivity of several reference liquids and selected biological tissues in vivo was measured in the frequency range from 0.01 to 1 GHz. Open-ended coaxial line sensors and computer-controlled network analyzer systems, described in a companion paper, were used. The results were analyzed and compared with the estimated uncertainties. The described method proved to be convenient, fast, and relatively accurate for in vivo measurements.

Experimental feasibility study of confocal microwave imaging for breast tumor detection

Initial experimental verification of confocal microwave imaging for breast tumor detection is described. Simple phantoms, consisting of a PVC pipe and objects representing tumors, are scanned with resistively loaded monopole or horn antennas. Successful reduction of clutter and detection of a variety of two-dimensional objects is demonstrated.

Simple treatment of multi-term dispersion in FDTD

Three new simple and efficient algorithms are proposed for the numerical treatment of the multi-term Debye or Lorentz dispersion in the FDTD method. The formulation is based on the auxiliary differential equation, but requires much fewer operations than the published schemes. The approach is equivalent to the best higher order recursive schemes in terms of memory and computational expense, but without the linearity assumptions.