A finite element model for simulating acoustic streaming in cystic breast lesions with experimental validation

Streaming detection is an ultrasonic technique that can be used to distinguish fluid-filled lesions, or cysts, from solid lesions. With this technique, high intensity ultrasound pulses are used to induce acoustic streaming in cyst fluid, and this motion is detected using Doppler flow estimation methods. Results from a pilot clinical study were recently published in which acoustic streaming was successfully induced and detected in 14 of 15 simple breast cysts and four of 14 sonographically indeterminate breast lesions in vivo. In this study, the detected velocities were found to vary considerably among cysts and for different pulsing regimes. A finite element model of streaming detection is presented in this paper. This model is utilized to investigate methods of increasing induced acoustic streaming velocity while minimizing patient exposure to high intensity ultrasound during streaming detection. Parameters studied include intensity, frequency, acoustic beam shape, cyst diameter, cyst fluid protein concentration, and cyst fluid viscosity. The model, which provides both transient and steady-state solutions, is shown to predict trends in streaming velocity accurately. Experimental results from studies investigating the potential for nonlinear streaming enhancement in cysts are also provided.