Safety Assessment of Advanced Imaging Sequences II: Simulations

An automatic approach for simulating the emitted pressure, intensity, and mechanical index (MI) of advanced ultrasound imaging sequences is presented. It is based on a linear simulation of pressure fields using Field II, and it is hypothesized that linear simulation can attain the needed accuracy for predicting MI and I(spta.3) as required by FDA. The method is performed on four different imaging schemes and compared to measurements conducted using the SARUS experimental scanner. The sequences include focused emissions with an F-number of 2 with 64 elements that generate highly nonlinear fields. The simulation time is between 0.67 and 2.8 ms per emission and imaging point, making it possible to simulate even complex emission sequences in less than 1 s for a single spatial position. The linear simulations yield a relative accuracy on MI between -12.1% and 52.3% and for I(spta.3) between -38.6% and 62.6%, when using the impulse response of the probe estimated from an independent measurement. The accuracy is increased to between -22% and 24.5% for MI and between -33.2% and 27.0% for I(spta.3), when using the pressure response measured at a single point to scale the simulation. The spatial distribution of MI and I(ta.3) closely matches that for the measurement, and simulations can, therefore, be used to select the region for measuring the intensities, resulting in a significant reduction in measurement time. It can validate emission sequences by showing symmetry of emitted pressure fields, focal position, and intensity distribution.