A comparison of beamforming methods for microwave breast cancer detection in homogeneous and heterogeneous tissue

Currently, X-rays and ultrasound are mainly used for the detection of breast cancer. However, their application is limited for mass-screenings since X-ray mammography is based on ionizing radiation and ultrasound alone provides too low specificity. It is possible, therefore, to use low-power microwave radiation in the frequency range between 0.1 and 10 GHz to localize the tumor by exploiting the dielectric contrast between malignant and healthy tissue. A major challenge for current microwave systems for breast cancer detection is given by the heterogeneity of the breast. To study the impact of tissue heterogeneity, we propose on one hand an ultrafast ray-tracing procedure for the simulation of microwave propagation in dispersive, heterogeneous media. Furthermore, we discuss the point spread functions, i.e. the theoretical imaging performance, of four beamforming reconstruction methods, i.e. delay-and-sum, time-difference-of-arrival, beamforming based on the coherence factor and the channel ranked beamformer.