Numerical study of microbubble dynamics subject to ultrasound and its effect on thermal ablation of biological tissue

High-intensity focused ultrasound (HIFU) provides many therapeutic applications for physicians. One of the ways to increase the efficiency of HIFU is using a levovist contrast agent, which consists of microbubbles. We calculate the pressure field of HIFU using the Helmholtz equation for linear ultrasonic propagation. Using the Keller-Miksis equation, we calculate the thermal effects caused by microbubble injection after determining the acoustic pressure. The Pennes bioheat transfer equation was used for the tissue temperature distribution. The present simulation results show that in the presence of a microbubble under the influence of HIFU pressure field, increasing the applied frequency and power increases the value of heat sources caused by microbubble oscillation. An increase in the temperature of biological tissue can be observed after the injection of microbubbles. In the pressure range of 2.54 MPa, the temperature of the tissue at the focal point, for the case where the microbubble with the initial radius of 50 μm is injected, increases by 8.28 ℃. Meanwhile, if a microbubble with an initial radius of 50 micrometers is injected, the temperature of the tissue increases by 57.72% more than before. However, the temperature of this point increased by only 5.42 ℃ in the same conditions in the absence of microbubbles. Finally, the Arrhenius model showed that microbubbles with different initial radii increased the volume of ablation tissue by about 38%.