Spectral and temporal signal modifications occuring between stable and transient inertial cavitation

The goal of this work is to investigate temporal and spectral modifications in passive cavitation detection (PCD) measurements from ultrasound contrast microbubbles (MBs) related to MB rupture. Contrast MB pressure-time responses are modelled with the Marmottant model. Results demonstrate that post-excitation signals occur on simulated pressure-time traces for MBs only when radial oscillations exceed the modelled breakup radius within a range of sizes near the resonant size. PCD signals are acquired from MBs of Optison, Definity and Sonovue (acoustic excitation at 2.8-MHz, 5-cycle transmit; confocal 13-MHz receiver). Although data are acquired at relatively high incident acoustic pressures (peak rarefactional pressure of 1.6, 2.0 and 2.4 plusmn 0.2 MPa), subsets of data with and without post-excitation signals are identified for each MB type and pressure range. Post-excitation signals are used to identify which PCD signals indicate MB break-up [1] then average values of peak-to-peak voltage, 2
^nd
harmonic, 3
^rd
and 4
^th
harmonic and broadband noise are calculated for responses from groups of ruptured and nonruptured MBs for each pressure range and MB type. The signal to noise ratio (SNR) is high (10 to 49 dB) both for ruptured (with post-excitation signals) and nonruptured (no post-excitation signals) MBs for all pressures and MBs. The average parameter values from ruptured MBs are approximately 3 to 8 dB higher than for nonruptured MBs although differences vary with the type of MB. Results contribute to better understand the link between PCD spectral and temporal modifications and MB break-up.