Using passive cavitation detection to observe postexcitation response of ultrasound contrast agents

Abstract

Passive cavitation detection was used to improve the experimental characterization of single ultrasound contrast agent microbubble responses to short, large amplitude pulses. Two situations were examined: isolated microbubbles in an unconstrained environment, and isolated microbubbles flowing through a tube. The microbubbles were categorized according to a classification scheme based on the presence or absence of postexcitation signals, which are secondary broadband spikes that may follow the principle oscillation of the ultrasound contrast agent in response to an insonifying pulse. Experiments were conducted for different frequencies, peak rarefactional pressures, flow rates, and types of microbubble. Postexcitation activity was found to increase as frequency decreased, acoustic pressure increased, and flow rate increased. Additionally, lipidshelled microbubbles were found to exhibit greater postexcitation at lower acoustic pressure thresholds than albumin-shelled microbubbles.

Improving the Accumulation of Gold Nanoparticles Using Ultrasound and Microbubbles to Enhance Radiation Therapy

“…Changing the passively recorded signal to the frequency domain using a Fourier Transform, the strength of the signal across a range of frequencies can be analyzed. A typical method of analysis is the integrated cavitation dose (ICD) where the area under the Fourier transform is calculated to develop insight into bubble behavior 61 . The area can be analyzed in from different bounds or by an overall broadband signal to obtain general or more specific information about the bubble activity.…”

“…Demonstrated in a previous study, it has been determined that inertial cavitation threshold for this experimental design is at 620 kPa, showing great increases in bubble activity after that pressure threshold which supports the massive increase at 770 kPa 74 . In inertial cavitation, bubbles collapse generating a high magnitude broadband acoustic signal 61 such as was seen at 770 kPa. Thus, it is reasonable to suggest that the greatest increase in cellular accumulation of AuNP which is observed at 770 kPa is due to the change in bubble behavior to the inertial regime.…”

On the acoustic response of ultrasound and induced cell death

“…Active cavitation detector uses a pulse-echo technique, which transmits and receives ultrasound pulses using the same transducer [34]. In passive cavitation detection (PCD), one transducer emits the pressure wave while the other transducer is set only in receive mode, which listens to the signal emissions from microbubble passively [35].…”