This is the accepted version of the paper.This version of the publication may differ from the final published version.
Permanent repository link:http://openaccess.city.ac.uk/8364/ Link to published version: http://dx.doi.org/10.1109/TBME. 2015.2393256 Copyright and reuse: City Research Online aims to make research outputs of City, University of London available to a wider audience. Copyright and Moral Rights remain with the author(s) and/or copyright holders. URLs from City Research Online may be freely distributed and linked to. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TBME.2015.2393256, IEEE Transactions on Biomedical Engineering IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING -TBME-00837-2014.R2 recently [3]. Early diagnosis of breast cancer is one of the most challenging and important aspects for the management of the disease, as it may be possible to detect the cancer before it spreads [4]. Three commonly used screening methods for breast cancer are X-ray mammography [5], Ultrasound (US) [6], and Magnetic Resonance Imaging (MRI) [7]. A higher rate of false-positive examination results with US makes it less popular than mammography [8], whereas MRI is usually suggested to be used in conjunction with mammography [9]. Despite the merits of mammography, its deficiencies are evident: low sensitivity [10], painful breast compression [11], and radiation exposure from X-rays, which brings a potential threat of increasing the cancer risk [12]. The limitations of existing methods constitute a motivation for better options.In the last few decades, different modalities of microwave imaging for breast cancer detection, including passive, hybrid, and active approaches, have attracted considerable attention. The passive imaging techniques seek to identify tumors based on the temperature differences between normal and cancerous breast tissues with the aid of radiometers [13]-[14]. Hybrid approaches differentiate biological tissues by the distinctive acoustic waves radiated from the thermoelastic expansion when tissues are under microwave illumination [15]. Active methods distinguish normal and malignant breast tissues based on their contrast of dielectric properties at microwave frequencies [16]. Based on the reconstruction technique used, active detection methods can be categorized into microwave tomography and ultrawideband (UWB) radar based imaging. In microwave tomography, the spatial distributions of dielectric constant and/or conductivity within the breast are iteratively calculated, thus nonlinear inverse scattering problems are involved. More details on tomographic imaging systems can be found in [17], [18]. UWB radar methods, on the other hand, aim to identify the presence and location of strong scatterers such as tumors, rather than quantitatively computing the distribution of dielectric properties.UWB radar based imaging systems face several challenges for breast...