The magnitude of radiation force on ultrasound contrast agents.

High-speed photography of insonified bubbles with a time resolution of 10 ns allows observations of translation due to radiation force, in addition to the visualization of radial oscillations. A modified version of the Rayleigh-Plesset equation is used to estimate the radius-time behavior of insonified microbubbles, and the accuracy of this model is verified experimentally. The translation of insonified microbubbles is calculated using a differential equation relating the acceleration of the bubble to the forces due to acoustic radiation and the drag imposed by the fluid. Simulations and experiments indicate that microbubbles translate significant distances with clinically relevant parameters. A 1.5 micron radius contrast agent can translate over 5 microns during a single 20-cycle, 2.25 MHz, 380 kPa acoustic pulse, achieving velocities over 0.5 m/s. Therefore, radiation force should be considered during an ultrasonic examination because of the possibility of influencing the position and flow velocity of the contrast agents with the interrogating acoustic beam.