Numerical simulations of heating patterns and tissue temperature response due to high-intensity focused ultrasound

The results of this paper show-for an existing high intensity focused ultra sound (HIFU) transducer-the importance of nonlinear effects on the space/ti me properties of wave propagation and heat generation in perfused liver mod els when a blood vessel also might be present. These simulations are based on the nonlinear parabolic equation for sound propagation and the bio-heat equation for temperature generation. The use of high initial pressure in HI FU transducers in combination with the physical characteristics of biologic al tissue induces shock formation during the propagation of a therapeutic u ltrasound wave. The induced shock directly affects the rate at which heat i s absorbed by tissue at the focus without significant influence on the magn itude and spatial distribution of the energy being delivered. When shocks f orm close to the focus, nonlinear enhancement of heating is confined in a s mall region around the focus and generates a higher localized thermal impac t on the tissue than that predicted by linear theory. The presence of a blo od vessel changes the spatial distribution of both the heating rate and tem perature.