Numerical simulations of tissue heating created by high-intensity focused ultrasound

Abstract

Modeling of high-intensity focused ultrasound (HIFU) propagation and heating effects in tissue has usually been studied under the assumption of linear acoustics. Nevertheless, nonlinear propagation can lead to important differences in heat deposition depending on the degree of nonlinearity achieved in a HIFU field. To be presented are calculations of the spatial patterns of acoustic intensity (I) and heat generation [H=−(∂/∂z+1/r∂/∂r)I for strongly nonlinear acoustic waves and H=2αI for weakly nonlinear acoustic waves, where α is acoustic absorption] associated with focused weakly and strongly nonlinear acoustic wave propagation in biological tissue. The propagation is modeled using a KZK equation method with special attention to correct modeling of shock generation and biologically relevant attenuation, as well as using initializing data based on existing designs of transducers for acoustic hemostasis. The heat generation term forces the ‘‘bio-heat’’ equation, which predicts the generation, movement, and dissipation of heat within biological tissue. The tissue model contains blood flow in an artery or vein and is perfused by a capillary bed. For this talk the differences in spatial patterns of acoustic intensity created by weakly and strongly nonlinear CW 1-Mhz acoustic wave propagation are shown. How those differences translate into differences in heat generation and therefore bioeffect within biological tissue are then demonstrated. [Work sponsored by DARPA.]