EXTRACTION OF PRESSURE AND TEMPERATURE DISTRIBUTION OF HIGH INTENSITY FOCUSED ULTRASOUND CONSIDERING NONLINEAR PROPAGATION

Abstract

The aim of this study is the extraction of acoustic pressure distribution in the target tissue layers based on the nonlinear behavior of waves. The nonlinear behavior effect of high intensity focused ultrasound (HIFU) on the temperature distribution of the tissue was extracted and compared with the linear behavior. The acoustic pressure field was calculated using the Westervelt equation and was coupled with Pennes thermal transfer equation. The simulations were performed for three layers of skin, fat and muscle using Comsol software. The disagreement between two linear and nonlinear models was analyzed with Kolmogorov–Smirnov test. The pressure and temperature distributions were calculated in nonlinear model by changing the acoustical parameters of the transducer including intensity, effective radiation area, focal length and sonication time. Model results were validated with experimental results with 98% correlation coefficient ([Formula: see text]). There is no significant difference between the pressure amplitude and temperature distribution in linear and nonlinear models at low intensity ([Formula: see text]), but with increasing intensity to 10[Formula: see text]W/cm2, in nonlinear model, maximum pressure and maximum temperature increased 40% and 20% compared with linear model. For input intensities of 1.5, 2, 8 and 10[Formula: see text]W/cm2, the maximum pressure (at focal point) increased 10%, 12%, 22%, 40% and maximum temperature increased 1%, 2%, 12%, 20% in nonlinear model compared to linear model. At 0.8[Formula: see text]cm2 and 1.5[Formula: see text]cm2 effective radiation area, the maximum acoustic pressure and temperature in nonlinear model increased from 12[Formula: see text]MPa to 30[Formula: see text]MPa and 43∘C to 79∘C, respectively. By decreasing the focal lengths from 10[Formula: see text]mm to 7.5[Formula: see text]mm, the maximum temperature increased from 45∘C to 87∘C. It is concluded a change in the input parameters of the transducer; it can be very effective in treating. The results emphasize the effects of nonlinear propagation and acoustical radiation parameters to improve the HIFU treatment.