Abstract
Acoustic properties of ultrasound (US) contrast agent microbubbles (MB)
highly influence sonoporation efficiency and intracellular drug and gene
delivery. In this study we propose an acoustic method to monitor passive
and excited MBs in a real time. MB monitoring system consisted of two
separate transducers. The first transducer delivered over an interval of 1
s US pulses (1 MHz, 1% duty cycle, 100 Hz repetition frequency) with
stepwise increased peak negative pressure (PNP), while the second one
continuously monitored acoustic response of SonoVue MBs. Pulse echo
signals were processed according to the substitution method to calculate
attenuation coefficient spectra and loss of amplitude. During US exposure
at 50–100 kPa PNP we observed a temporal increase in loss of amplitude
which coincided with the US delivery. Transient increase in loss of
amplitude vanished at higher PNP values. At higher PNP values loss of
amplitude decreased during the US exposure indicating MB sonodestruction.
Analysis of transient attenuation spectra revealed that attenuation
coefficient was maximal at 1.5 MHz frequency which is consistent with
resonance frequency of SonoVue MB. The method allows evaluation of the of
resonance frequency of MB, onset and kinetics of MB sonodestruction.
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