Experimental Evaluation of an Axillary Microwave Imaging System to Aid Breast Cancer Staging

Abstract

The number of metastasised Axillary Lymph Nodes (ALNs) is a key indicator for breast cancer staging. Its correct assessment affects subsequent therapeutic decisions. Common ALN screening modalities lack high enough sensitivity and specificity. Level I ALNs produce detectable backscattering of microwaves, opening the way for Microwave Imaging (MWI) as a complementary screening modality. Radar-based MWI is a low-cost, non-invasive technique, widely studied for breast cancer and brain stroke detection. However, new specific challenges arise for ALN detection, which deter a simple extension of existing MWI methods. The geometry of the axillary region is more complex, limiting the antenna travel range required for maximum resolution. Additionally, unlike breast MWI setups, it is impractical to use liquid immersion to enhance energy coupling to the body; therefore, higher skin reflection masks ALNs response. We present a complete study that proposes dedicated imaging algorithms to detect ALNs dealing with the above constraints, and evaluate their effectiveness experimentally. We describe the developed setup based on a 3D-printed anthropomorphic phantom, and the antenna-positioning configuration. To the authors' knowledge, this is the first ALN-MWI study involving a fully functional anatomically compliant setup. A Vivaldi antenna, operating in a monostatic radar mode at 2-5 GHz, scans the axillary region. Pre-clinical assessment in different representative scenarios shows Signal-to-Clutter Ratio higher than 2.8 dB and Location Error lower than 15 mm, which is smaller than considered ALN dimensions. Our study shows promising level I ALN detection results despite the new challenges, confirming MWI potential to aid breast cancer staging.

Target Selection in Multistatic Microwave Breast Imaging Setup Using Dielectric Lens

“…We use Singular Value Decomposition (SVD) as artefact removal algorithm, which has been used for monostatic airoperated imaging setups [9], [10]. SVD computes the factorisation of a real or complex matrix M of signals into three matrices of singular vectors and singular values [9].…”

“…The quality of the reconstructed images are evaluated using state-of-the-art performance metrics: Signal-to-Clutter Ratio (SCR), Signal-to-Mean Ratio (SMR), Full Width Half Maximum (FWHM) and Localisation Error (LE) [10].…”

Evaluating the Performance of Algorithms in Axillary Microwave Imaging towards Improved Breast Cancer Staging

“…Also, MWI presents several advantages compared to other imaging systems, namely the fact that it uses non-ionizing radiation, it is non-invasive, it is potentially low-cost and can be portable [ 13 ]. Recently, MWI has been studied for the early non-invasive detection of ALNs [ 15 , 16 , 17 , 18 ]. In most recent work [ 16 , 17 , 18 ], anatomically realistic models of the axillary region have been used to test these MWI systems.…”

“…Recently, MWI has been studied for the early non-invasive detection of ALNs [ 15 , 16 , 17 , 18 ]. In most recent work [ 16 , 17 , 18 ], anatomically realistic models of the axillary region have been used to test these MWI systems.…”

Effect of Varying Prior Information in Axillary 2D Microwave Tomography

“…The possibility of imaging ALNs using microwave imaging (MWI) is under study in our research group [4], [5], [6], [7], and other authors in the literature considered such possibility [8]. However, axillary MWI presents considerable challenges if compared to other medical-MWI applications: here, given the morphology of the axilla, antennas cannot be placed in a circular configuration, but only in a limited arc around the area of interest (≈ 90 • ), significantly limiting the information available for image reconstruction.…”