Postexcitation collapse as a characteristic of single ultrasound contrast agent destruction

Abstract

Measurement of the response of single, unconstrained ultrasound contrast agents (UCAs) is useful for facilitating experiment interpretation and theoretical comparison. An experimental setup has been developed to characterize the acoustic large amplitude response of microbubbles called double passive cavitation detection (PCD) which consists of three confocally aligned transducers. The symmetric single bubble responses from within the confocal region are analyzed for the presence or absence of a postexcitation signal (PES), a rebound characteristic response to large amplitude pressures that may follow the initial harmonic UCA response. Experimental sensitivity to the PES is explored by receiving with transducers of different frequencies. Theoretical models indicate postexcitation rebound occurs following shell rupture and inertial cavitation of the UCA. The postexcitation response curves as a cavitation metric are useful for characterizing distinct collapse thresholds among UCAs which arise due to material differences; additionally, the thresholds may be considered as destruction thresholds and compared to a variety of in-vitro and in-vivo studies to aid in understanding the resultant bioeffects in these studies. (NIH Grant R37EB002641.)