Estimating the Effective Permittivity for Reconstructing Accurate Microwave-Radar Images.

Benjamin R Lavoie,Michal Okoniewski,Elise C Fear,Luis Carretero

doi:10.1371/journal.pone.0160849

Abstract

We present preliminary results from a method for estimating the optimal effective permittivity for reconstructing microwave-radar images. Using knowledge of how microwave-radar images are formed, we identify characteristics that are typical of good images, and define a fitness function to measure the relative image quality. We build a polynomial interpolant of the fitness function in order to identify the most likely permittivity values of the tissue. To make the estimation process more efficient, the polynomial interpolant is constructed using a locally and dimensionally adaptive sampling method that is a novel combination of stochastic collocation and polynomial chaos. Examples, using a series of simulated, experimental and patient data collected using the Tissue Sensing Adaptive Radar system, which is under development at the University of Calgary, are presented. These examples show how, using our method, accurate images can be reconstructed starting with only a broad estimate of the permittivity range.

Highlights

Near-field ultra-wide-band (UWB) microwave imaging techniques are under development as complementary methods to existing medical imaging techniques [1,2,3,4,5,6,7,8,9,10]
Plots of Eq (2) as a function of the effective skin and interior tissue permittivities are presented, and images formed using the most likely permittivity values are compared with the known properties of the simulation/model, where available
Monostatic microwave-radar imaging systems require knowledge of the target’s permittivities in order to form an accurate image. This estimate can be directly obtained from time-of-flight measurements made with a separate measurement system. Such estimates are not always representative of the effective permittivity experienced by the microwave signals

Summary

Introduction

Near-field ultra-wide-band (UWB) microwave imaging techniques are under development as complementary methods to existing medical imaging techniques [1,2,3,4,5,6,7,8,9,10]. Microwave radar systems have attracted interest because of the potential for discriminating malignant tissue from surrounding material using a process that relies on different tissue properties than the existing techniques [12]. This allows the possibility of using microwave radar images to locate structures that could be missed by other imaging techniques. Microwaves are non-ionizing, in contrast to X-rays used for mammography or computed tomography (CT) scans, and there is no need for a contrast agent, which is often used in magnetic resonance imaging. This means that multiple scans can be performed within short time

Results

Discussion

Conclusion