Frequency dependence of microwave thermo-acoustic imaging of breast tumors and microcalcifications

Photoacoustic imaging has established itself as a prominent medical imaging modality. However, its efficacy is limited by its shallow penetration depth. Thermoacoustic imaging has been used for applications such as breast cancer imaging using RF/microwave sources for increased penetration depth; however, its use for detecting microcalcifications as precursors for breast tumors has not yet been established. Modelling thermoacoustic processes necessitates consideration of wave propagation within the tissue, which is currently under-represented in the literature. This study presents a comprehensive physics-based simulation model for microwave thermoacoustic imaging of breast tissues with embedded tumors/microcalcifications, incorporating electromagnetic wave propagation, heat transfer, and volumetric strain. The simulation results were validated by comparison with the experimental results, and the model was used to investigate the thermoacoustic signals at different microwave frequencies. The results revealed three major contributions, each prevailing within a specific frequency range. This distinction is crucial for optimizing the thermoacoustic setup for medical imaging.