Abstract:

Double passive cavitation detection involves the confocal alignment of one transmit and two passive receive transducers. Highly dilute mixtures of ultrasound contrast agents (UCAs), including Definity, Optison, and non‐commercial microbubbles, were prepared such that on average only a single UCA was present at the confocal region. A 3‐cycle incident pulse repeating at 10 Hz was varied in frequency from 0.9 to 7.1 MHz and in peak rarefactional pressure (PRP) from 200 kPa to 6 MPa. The acquired signals were classified according to the presence or absence of a postexcitation signal (PES), a quantifiable aspect of the acquired temporal signal which is hypothesized to occur due to the rupture of the UCA shell and therefore indicate the collapse of the microbubble. The resulting percentages of UCAs with PES were fitted with modified logistic regression curves to determine percentage collapse thresholds. The percentage of signals exhibiting PES was found to increase as frequency decreased or as PRP increased while holding other acoustic parameters constant, in agreement with alternative methods of measuring collapse. Definity was found to have a lower threshold of collapse than Optison, while the thresholds of the non‐commercial UCAs depended on their physical properties. (Work supported by NIH Grant No. R37EB002641.)