Improved Confocal Microwave Imaging of the breast using path-dependent signal weighting

Abstract

Confocal Microwave Imaging (CMI) using Ultra Wideband Radar (UWB) for the early detection of breast cancer is based on several assumptions regarding the dielectric properties of normal and malignant breast tissue. One of these assumptions is that the breast is primarily dielectrically homogeneous, and that the propagation, attenuation and phase characteristics of normal breast tissue allows for the constructive addition of the Ultra Wideband (UWB) returns from dielectric scatterers within the breast. However, recent studies by Lazebnik et al. have highlighted a very significant dielectric contrast between normal adipose and fibroglandular tissue within the breast. This dielectric heterogeneity presents a considerably more challenging imaging scenario, where constructive addition of the UWB returns, and therefore tumor detection, is much more difficult. In a dielectrically homogeneous breast, each additional beamformed backscattered signal adds coherently with existing signals, resulting in an improved image of any dielectric scatterers present. If attenuation and phase effects are compensated for appropriately, each signal will provide equal information about the location of the scatterer within the breast. However, in a dielectrically heterogeneous breast, not all propagation paths are equal. For a particular synthetic focal point within the breast, some channels will be blocked by significant regions of dielectric heterogeneity (fibroglandular tissue), while others will a clear “view” of the point of interest. Rather than giving each category of channel equal weighting (as is the case for traditional CMI), the channels with a better “view” of the point should be given extra weighting. However, rewarding a subset of the recorded channels may also reduce the effective spatial diversity of the antennas, and therefore a compromise must be achieved between rewarding the best channels, while retaining effective spatial diversity. An improved CMI beamformer is proposed in this paper, and is shown to provide improved images of more dielectrically heterogeneous breasts than the traditional delay and sum beamformer from which it is derived.