An improved understanding of ultrasound contrast agent (UCA) shell rupture is required to optimize therapeutic and diagnostic use. This experimental and theoretical study aims to explore the mechanism of UCA shell rupture by determining thresholds as a function of ultrasonic excitation parameters (driving frequency, pulse duration, and peak rarefactional pressure). The experimental setup is based on a passive cavitation detection system described in previous work. However, this system has been modified to allow simultaneous acquisition of the signals received with the 13-MHz passive receiver and the signals incident upon the lower frequency (0.9, 2.8 and 4.6 MHz) transmitting transducer functioning in the pulse-echo mode. Post-excitation signals were used to detect rupture thresholds. By allowing acquisition of the signals received by the insonifying transducer (pulse-echo during the excitation and passively at post-excitation) additional information is obtained within a frequency range and a transmission/reception configuration typical of ultrasonic diagnostic imaging. Data are analyzed to estimates the incident peak rarefactional pressure leading to 50% destruction. Comparison of experimental results with microbubble dynamics predicted using the Modified Herring equation was used to explore microbubble rupture indices based on radial expansion and peak velocity.