Effect of cross-sectional area of high-intensity focused ultrasound (HIFU) on the thermal distribution of the target tissue

HIFU technology is a non-invasive treatment method based on the conversion of acoustic energy into thermal energy focused on the target area. In this study, the effect of radiation cross- section on heat distribution in the target tissue is investigated. To investigate the effect of radiation cross- section, in this study, finite element method and COMSOL simulation software were used in the linear emission mode of ultrasonic waves. At a maximum input sound intensity of 10 W/cm2, the pressure wave equation was solved by considering thermo-viscous fluid at two cross- sections of 1.5 and 0.8 cm2. Based on the Pennes heat transfer equation, the heat field distribution in skin tissue, subcutaneous fat, and muscle was calculated. To validate the simulation results, the correlation between the results of the mathematical model the experimental method with a 95% confidence level (p<0.05) was evaluated. At an input sound intensity of 10 W/ cm2 and at a focal length of 4.5 mm from the skin surface, with an increase in cross- section from 0.8 to 1.5 cm2, the maximum sound pressure from 8.6 to 20.9 MPa and the maximum temperature from 60 to 139 °C. The results showed that the sound pressure distribution and the thermal dose of the target tissue depended on the cross-sectional area of the sound transducers. It is concluded that in order to achieve the selected treatment protocol, the treatment plan should be simulated based on radiation input and physical characteristics of the tissue.