Passive cavitation detection analysis of materials with varying levels of color Doppler twinkling.

The mechanism of color Doppler twinkling has been previously associated with microbubbles through various experiments. As there has been limited work directly showing evidence of bubble oscillation simultaneously with twinkling, passive cavitation detection (PCD) was used to record raw radiofrequency (RF) signals from twinkling objects that could contain microbubble information. Polymethyl methacrylate (PMMA) twinkling markers and non-twinkling samples were evaluated in a PCD setup using a single element passive cavitation detection transducer while varying transmitted peak negative pressures with an L11-4v linear transducer. Recorded PCD data was analyzed in both the time and frequency domains for evidence of bubbles. In the time domain, twinkling markers were found to have more pulse-to-pulse voltage variation than low and non-twinkling samples. In the frequency domain, twinkling markers were found to have higher magnitudes in the inharmonic bands compared to the low and non-twinkling samples. When varying the peak negative pressure of the ultrasound waves from low to high, both the time domain variation and frequency domain inharmonic bands were found to correlate with twinkling (P < 0.043 and P < 0.037, respectively). These results support microbubble oscillation as a cause of twinkling, particularly from the likely presence of inertial cavitation of microbubbles.