Comparison of spectral and temporal criteria for Inertial Cavitation collapse

Dilute solutions of Optison and Definity were studied using a passive cavitation detector (PCD) with a 2.8-MHz transmitter and 13-MHz receiver. The dilution was such that each received signal should, on average, arise from a single microbubble. Several hundred microbubble responses were acquired at each of three rarefactional pressure ranges (1.6+/-0.2, 2.0+/-0.2 and 2.4+/-0.2 MPa). Each microbubble response was grouped with signals presenting post-excitation emissions (transient Inertial Cavitation) or those with no evidence of post-excitation emission (non-transient Inertial Cavitation). For each incident pressure, we compared discrimination of signals from the two groups according to peak-voltage, broadband noise (12-17.6 MHz) and power at the fundamental, 2^nd, 3^rd, and 4^th harmonic peaks. In addition to increased peak-voltage and broadband noise, spectra from transient IC groups consistently presented increased 2^nd, 3^rd and 4 ^th harmonics compared to the Non-Transient IC group. Throughout the studied pressure range, best separation between the two groups was obtained with peakvoltage (4.7+/-1.8dB), broadband noise (4.4+/-1.8) and 4^th harmonic (5.6+/-2.2) for Optison. For Definity, all harmonics (2^nd to 4^th) increased strongly for the transient IC group (approximately 6 dB) as well as peak-voltage (5.3+/-1.2dB) and broadband noise (5.8+/-2dB). Results should contribute to relating PCD criteria to IC activity.