The temperature enhancement effect of magnetic microbubble agents induced by focused ultrasound exposures under different flow rate conditions

To further understand the changes in temperature enhancement effects induced by high-intensity focused ultrasound (HIFU) in fluid environments such as blood, this study prepared dual-modal magnetic microbubbles that can be used as contrast agents for both ultrasound and magnetic resonance imaging. The study measured the acoustic attenuation coefficient of dual-modal magnetic microbubble solutions loaded with different concentrations of superparamagnetic iron oxide (SPIO) nanoparticles. Gel phantoms were prepared, and the ability of microbubbles to enhance HIFU thermal effects under different flow rates were measured using temperature probes after ultrasound irradiation. Finally, finite element method was conducted to simulate the experimental environment and compared with experimental results. The results showed that compared to traditional protein microbubbles, magnetic microbubble solutions exhibited higher acoustic attenuation coefficients and specific heat capacities. Increasing the concentration of SPIO nanoparticles mounted on the microbubble membrane led to faster temperature elevation and higher peak temperatures locally. The effect of solution flow rate on temperature changes in magnetic microbubble solutions was complex; generally, fluid flow weakened the temperature accumulation effect of the microbubble solution under ultrasound irradiation.