Ultrasonic excitation of a bubble near a rigid or deformable sphere: implications for ultrasonically induced hemolysis.

A number of independent studies have reported increased ultrasound bioeffects, such as hemolysis and hemorrhage, when ultrasound contrast agents are present. To better understand the role of cavitation in these bioeffects, one- and two-dimensional models have been developed to investigate the interactions between ultrasonically excited bubbles and model "cells." First, a simple one-dimensional model based on the Rayleigh-Plesset equation was developed to estimate upper bounds for strain, strain rate, and areal expansion of a simulated red blood cell. Then, two-dimensional boundary element models were developed (with DynaFlow Inc.) to obtain simulations of asymmetric bubble dynamics in the presence of rigid and deformable spheres. The deformable spherical "cell" was modeled using Tait's equation of state for water, with a membrane approximated by surface tension that increases linearly with areal expansion. The presence of a rigid or deformable sphere had little effect on the bubble expansion, but caused an asymmetric collapse and jetting for the conditions considered. Predicted membrane areal expansions were found to be below critical values for hemolysis reported in the literature for the cases considered near the inertial cavitation threshold.