Ultra-wideband Microwave Imaging Research Articles

WEIGHTED CENTROID METHOD FOR BREAST TUMOR LOCALIZATION USING AN UWB RADAR

This paper studies the potential of ultra-wideband (UWB) microwave imaging for detection and localization of breast cancer in its early stages. A method is proposed for locating tumors which is based on the time-of-∞ight of the signal backscattered at the tumor. Time- of-∞ight is detected using a wavelet transform algorithm. The main contribution of this paper is that it proposes to determine the position of the tumor by using an adapted version of the centroid localization method used in wireless sensor nodes. Its main advantage is that it does not require knowing a priori neither the propagation velocity of the breast nor its dielectric permittivity. The feasibility of the method has been investigated by means of simulated and experimental results with an ultra-wideband radar and a phantom.

The Effects of Breast Tissue Heterogeneity on Data-adaptive Beamforming

Ultrawideband (UWB) Microwave Imaging is an emerging technology for breast cancer detection which is based on the dielectric contrast between normal and cancerous tis- sues at microwave frequencies. The breast is illuminated by a UWB pulse and re∞ected signals are used to determine the presence and location of signiflcant dielectric scatterers, which may be representative of cancerous tissue within the breast. Beamformers are used to spatially fo- cus the re∞ected signals and to compensate for path dependent attenuation and phase efiects. These beamformers can be divided into two distinct categories: Data-Independent and Data- Adaptive beamformers. Data-Independent beamformers typically use an assumed channel model to compensate for path-dependent propagation efiects. Conversely, Data-Adaptive beamformers attempt to directly estimate the actual channel based on signals re∞ected from the breast. Recent studies by Lazebnik etal. indicate that the range of dielectric properties of normal breast tissue is much greater than reported previously. This presents a much more di-cult imaging prob- lem due to dielectric heterogeneity. Di-culties encountered by data-independent beamformers in locating tumors within dielectrically heterogeneous breasts have been documented previously. In this paper, the efiects of heterogeneity on data-adaptive beamformers is investigated. 2D MRI-derived breast models with varying levels of dielectric heterogeneity are used to evaluate the data-adaptive beamformers.

HOMOGENEOUS AND HETEROGENEOUS BREAST PHANTOMS FOR ULTRA-WIDEBAND MICROWAVE IMAGING APPLICATIONS

The paper discusses fabrication of homogenous and heterogeneous breast phantoms to simulate the dielectric properties of human breast over the microwave frequency range from 0.5GHz to 13.5GHz. The breast phantoms have stable mechanical conflguration and dielectric properties suitable for microwave imaging experiments particularly ultra-wideband microwave imaging for breast cancer detection.

Compact directional antenna for ultra wideband microwave imaging system

AbstractA planar antenna of tapered slot configuration for use in ultra wideband microwave imaging systems aimed for early breast cancer detection is presented. It is designed to operate across the ultra wideband frequency (3.1–10.6 GHz) in a liquid of a high dielectric constant that matches the electric properties of average breast tissues. It has a very compact size with overall dimensions of 0.9 cm × 1 cm. The antenna's ultra wideband performance even when it is close to the breast tissues and its distortionless response in the time domain make it suitable for the microwave imaging systems utilizing a short‐pulse radar technique. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2898–2901, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24764

Ultrawideband Microwave Sensing and Imaging Using Time-Reversal Techniques: A Review

This paper provides an overview of some time-reversal (TR) techniques for remote sensing and imaging using ultrawideband (UWB) electromagnetic signals in the microwave and millimeter wave range. The TR techniques explore the TR invariance of the wave equation in lossless and stationary media. They provide superresolution and statistical stability, and are therefore quite useful for a number of remote sensing applications. We first discuss the TR concept through a prototypal TR experiment with a discrete scatterer embedded in continuous random media. We then discuss a series of TR-based imaging algorithms employing UWB signals: DORT, space-frequency (SF) imaging and TR-MUSIC. Finally, we consider a dispersion/loss compensation approach for TR applications in dispersive/lossy media, where TR invariance is broken.

WAVELET-BASED BREAST TUMOR LOCALIZATION TECHNIQUE USING A UWB RADAR

This paper deals with the potential of ultra-wideband (UWB) microwave imaging for the detection and localization of breast cancer in its early stages. A method is proposed for locating tumors which is based on the signal time-of-∞ight backscattered by the tumor. Time-of-∞ight is detected using a wavelet transform algorithm. The feasibility of the method has been investigated by means of simulated results using Finite-Difierence Time-Domain (FDTD) and experimental results with a UWB radar and a phantom.

Ultra-wideband microwave imaging of heterogeneities

The technique of time-reversal acoustics was applied to image a bottle filled with saline, using an eight element Vivaldi antenna array with frequency bandwidth 2 to 8 GHz. At these short length scales, a smooth three-dimensional image of the bottle was obtained, with the usual limitations imposed by limited offset and frequency. Time snapshots of the wavefield evolution, in reversed time are presented for two real data sets. The first, shows the focusing for the single target of the bottle, while the second demonstrates the principle for two targets.

Confocal Microwave Imaging for Breast Cancer Detection: Delay-Multiply-and-Sum Image Reconstruction Algorithm

A new image reconstruction algorithm, termed as delay-multiply-and-sum (DMAS), for breast cancer detection using an ultra-wideband confocal microwave imaging technique is proposed. In DMAS algorithm, the backscattered signals received from numerical breast phantoms simulated using the finite-difference time-domain method are time shifted, multiplied in pair, and the products are summed to form a synthetic focal point. The effectiveness of the DMAS algorithm is shown by applying it to backscattered signals received from a variety of numerical breast phantoms. The reconstructed images illustrate improvement in identification of embedded malignant tumors over the delay-and-sum algorithm. Successful detection and localization of tumors as small as 2 mm in diameter are also demonstrated.

Estimating the Breast Surface Using UWB Microwave Monostatic Backscatter Measurements

This paper presents an algorithm for estimating the location of the breast surface from scattered ultrawideband (UWB) microwave signals recorded across an antenna array. Knowing the location of the breast surface can improve imaging performance if incorporated as a priori information into recently proposed microwave imaging algorithms. These techniques transmit low-power microwaves into the breast using an antenna array, which in turn measures the scattered microwave signals for the purpose of detecting anomalies or changes in the dielectric properties of breast tissue. Our proposed surface identification algorithm consists of three procedures, the first of which estimates M points on the breast surface given M channels of measured microwave backscatter data. The second procedure applies interpolation and extrapolation to these M points to generate N > M points that are approximately uniformly distributed over the breast surface, while the third procedure uses these N points to generate a 3-D estimated breast surface. Numerical as well as experimental tests indicate that the maximum absolute error in the estimated surface generated by the algorithm is on the order of several millimeters. An error analysis conducted for a basic microwave radar imaging algorithm (least-squares narrowband beamforming) indicates that this level of error is acceptable. A key advantage of the algorithm is that it uses the same measured signals that are used for UWB microwave imaging, thereby minimizing patient scan time and avoiding the need for additional hardware.

An Ultra Wideband Microwave Imaging System for Breast Cancer Detection

An experimental study concerning Ultra Wideband (UWB) Microwave Radar for breast cancer detection is described. A simple phantom, consisting of a cylindrical plastic container with a low dielectric constant material imitating fatty tissues and a high dielectric constant object emulating turnout, is scanned with a tapered slot antenna operating between 3.1 to 10.6 GHz. A successful detection of a target is accomplished by a visual inspection of a two-dimensional image of the scanned phantom.

An overview of ultra-wideband microwave imaging via space-time beamforming for early-stage breast-cancer detection

Ultra-wideband (UWB) microwave imaging has recently been proposed for detecting small malignant breast tumors. In this article, we review the current research status of this approach. First, we introduce the concept of microwave imaging via space-time (MIST) beamforming and related signal-processing algorithms. The objective of these signal-processing techniques is to form a spatial image of scattered microwave energy, and to identify the presence and location of malignant lesions from their scattering signatures. Next, we present numerical studies based on finite-difference time-domain simulations to demonstrate the efficacy of MIST beamforming for detecting small malignant breast lesions in both prone and supine configurations. Finally, the experimental feasibility of UWB microwave imaging is demonstrated using an initial imaging prototype and multilayered breast phantoms.

TIME-DOMAIN ULTRA-WIDEBAND MICROWAVE IMAGING RADAR SYSTEM

This paper describes the time-domain (TD) ultrawideband (UWB) microwave imaging radar system developed at the University of Illinois at Urbana-Champaign recently. The TD-UWB imaging radar system successfully combines the UWB impulse radar system and inverse scattering imaging algorithms for nondestructive evaluation (NDE) and remote sensing purposes in the near-field region. Both the system hardware and inverse scattering algorithms of the system will be discussed in this paper. The TD-UWB imaging radar system can detect dielectric or metallic targets located in air or shallow subsurface with a high resolution image reconstruction capability. Reconstructed images of different types of targets are shown to be in good agreement with the target geometry. The experimental results demonstrate the potential of the system as an useful tool for NDE and remote sensing applications.

A confocal microwave imaging algorithm for breast cancer detection

We present a computationally efficient and robust image reconstruction algorithm for breast cancer detection using an ultrawideband confocal microwave imaging system. To test the efficacy of this approach, we have developed a two-dimensional (2-D) anatomically realistic MRI-derived FDTD model of the cancerous breast. The image reconstruction algorithm is applied to FDTD-computed backscatter signals, resulting in a microwave image that clearly identifies the presence and location of the malignant lesion. These simulations demonstrate the feasibility of detecting and imaging small breast tumors using this novel approach.