What is the role of microwave imaging for breast cancer detection?

Microwave imaging for breast cancer detection exploits the significant difference in dielectric properties between malignant tumors and normal breast tissue at microwave frequencies (1-10 GHz). Malignant breast tumors have dielectric constant (Er) approximately 2-5 times higher than surrounding normal breast tissue (tumor: Er = 40-60, normal breast tissue: Er = 10-20 at 3 GHz) and higher conductivity (tumor: 2-4 S/m, normal: 0.5-1.5 S/m). This dielectric contrast creates reflections and scattering when microwave signals illuminate the breast, which can be processed to form images showing tumor locations. Two main approaches exist: microwave radar imaging (transmit short UWB pulses or wideband swept signals into the breast from an array of antennas surrounding the breast; process the backscattered signals using beamforming or tomographic algorithms to reconstruct a 3D image of the dielectric property distribution), and microwave tomography (measure the transmitted and scattered fields between all pairs of antennas in the array; use iterative inverse-scattering algorithms to reconstruct the 2D or 3D dielectric property map of the breast). The advantages over X-ray mammography include: no ionizing radiation (safe for frequent screening, especially for young women), no breast compression required (improved patient comfort), sensitivity not affected by breast density (dense breasts are difficult to image with X-ray due to similar X-ray attenuation of dense tissue and tumors, but have high dielectric contrast with tumors at microwave frequencies), and lower cost (no X-ray source, lower facility requirements).