High intensity focused ultrasound and tissue heating: the effect of nonlinear sound propagation and vessel presence

The use of high initial pressures in high intensity focused ultrasound transducers combined with the physical characteristics of biological tissue are likely to induce shock formation during the propagation of an ultrasound wave. The induced shock directly affects the magnitude and spatial distribution of the energy being delivered as well as the rate at which heat is absorbed by tissue. The degree to which higher frequencies are created characterizes weakly-nonlinear and strongly-nonlinear regimes which are responsible for mild and strong deviations from the predictions of linear theory. Our numerical simulations, based on the KZK equation for sound propagation and the bioheat equation for temperature generation, show the importance of these effects for an existing transducer in perfused liver models where a blood vessel might also be present.