Mechanical properties of acoustic processes in microwave-induced thermoacoustic imaging

Microwave-induced thermoacoustic imaging (MITAI) is an emerging non-destructive biomedical imaging tool. It uses pulsed microwaves to cause a transient thermoelastic expansion in tissues, generating ultrasonic waves that are detected by acoustic transducers — combining the high contrast of microwave imaging, and the high resolution of ultrasound, to visualize targets by simultaneously presenting their dielectric properties and structural details.

In moving MITAI towards clinical applications, the finite element simulation software COMSOL Multiphysics has been particularly useful for testing the tool; however, it has rarely been used to characterize the full multi-physical phenomena involved in MITAI. Guo et al. filled this gap by designing a dual-imaging target model that couples electromagnetism, heat transfer, structural mechanics and pressure acoustics, with a focus on coupling the latter two to simulate microwave excitation, energy deposition, thermal expansion, and ultrasound propagation in the imaging process.

Thermoacoustic signals acquired from simulations were reconstructed into MITAI images, revealing artifacts with specific patterns. The authors created complex tissue models to investigate these markers of signal deflection, providing insight into how mechanical property differences between bone and soft tissue, as well as their proximity, form unique maps of ultrasonic propagation.

“Studying how tissue mechanical properties influence image quality and artifacts will offer a basis for understanding and correcting inherent defects in imaging complex tissues,” said author Zihui Chi.

Given the wide-ranging potential of MITAI in domains like cancer screening and joint assessment, the authors hope to accelerate its integration into clinical settings.

“Our future work will focus on using high-fidelity simulation to visualize signal and artifact features, and on designing advanced imaging algorithms, such as physics-informed reconstruction or deep-learning artifact removal, to improve image quality and promote broader clinical adoption of MITAI,” Chi said.

Source: “Multiphysics simulation of microwave-induced thermoacoustic imaging based on complete acoustic process and its application in bone artifact analysis,” by Xiangwen Guo, Zihui Chi, Zesong He, Lei Chen, Zhengyu Zhang, Yang Meng, and Huabei Jiang, Journal of Applied Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0308312 .