A theoretical model for the interaction of an ultrasound-activated contrast microbubble with a wall at arbitrary separation distances

A theoretical model is proposed that describes the dynamics of an ultrasound-activated contrast microbubble at arbitrary distances from a wall. The model consists of two coupled equations that describe the bubble radial oscillation and the translation of the bubble center. The equations make it possible to simulate the interaction of the microbubble with the wall starting from large distances and up to contact with the wall. Numerical simulations are performed to determine how the acoustic response of a contrast microbubble depends on separation distance near walls of different types: rigid, plastic, arterial, etc. The results of the simulations show that the bubble resonance frequency near a wall depends on both the separation distance and the wall material properties. In particular, the plastic and arterial walls make the resonance frequency increase with decreasing separation distance. The theoretical model is validated by comparing with experimental data available in the literature for individual phospholipid-shelled microbubbles near a compliant agarose gel boundary.