Analytic prediction of histotripsy-induced bubble growth in an elastic medium

Abstract

Histotripsy is a form of therapeutic ultrasound that liquefies tissue mechanically via acoustic cavitation. Bubble growth due to histotripsy excitation has been calculated analytically with high accuracy in a fluid medium. Tissue elasticity is a determining factor in the therapeutic efficacy of histotripsy, and has not been considered in analytic bubble dynamics calculations. In this study, an analytic model to predict histotripsy-induced bubble expansion based on the medium surface tension, viscosity, and inertia was extended to include the effects of medium stiffness. Good agreement was observed between the predictions of the model and numerical computations. The predictions of the model were also consistent with experimental observation of bubble expansion, though are dependent on the elasticity form. Bubble growth was weakly dependent on the medium elasticity for highly nonlinear, shock scattering histotripsy pulses, but was strongly dependent for purely tensile, microtripsy pulses. For both forms of histotripsy, bubble growth was completely suppressed when the elastic modulus exceeded 20 MPa and the peak negative pressures was less than 50 MPa. These results highlight the importance of the histotripsy insonation scheme on bubble growth in an elastic medium, as well the range of tissue elasticities for efficacious bubble-induced liquefaction.