Nonlinear pulse calculations and data in water and a tissue mimic

Abstract

Nonlinear propagation is recognized as an important aspect of ultrasonic medical imaging. In particular, rigorous estimates of tissue bioeffects must include it. Regulatory standards rely on measurements in water to estimate effects in lossy tissue, but nonlinearity confuses the relationship. To help clarify the connection the authors complement laboratory hydrophone data with computer simulations of acoustic pulses in water and a tofu tissue mimic. A 2.25 MHz focused disk transducer is used instead of a rectangular medical array to facilitate modeling with a 2D pseudospectral solver that includes causal attenuation, inhomogeneity, multiple reflections, nonlinearity, and shock smoothing. Pressure scans near the transducer characterize the source and drive the wave solver. Measured and calculated nonlinear acoustic fields are compared over a 6 cm range in water and behind tofu cylinders. In the absence of high drive data the authors rely on nonlinear simulations to contrast water and tofu results, in anticipation of derating studies.