Effects of pulse length and pulse repetition frequency on the stable cavitation characteristics of flowing microbubbles

A tissue phantom,with a customized ultrasound exposure system and an agarose-gel blood vessel to hold the SonoVue microbubbles was manufactured to give insight into effects of pulse length and pulse repetition frequency on the stable cavitation characteristics of flowing microbubbles.A 1 MHz focused transducer and another 7.5 MHz plane transducer were employed to emit the pulsed ultrasound and receive the cavitation signal respectively.Then the signal was amplified and recorded by a high-speed AD.After analyzed in time and frequency domains,we found that the Stable Cavitation Dose (SCD) was determined by both the Pulse Repetition Frequency (PRF) and the Pulse Length (PL).When PRF is smaller than the Critical Pulse Repetition Frequency (CPRF),SCD is positive related with the PL and has evenly distribution during the exposure time.However,the characteristics of stable cavitation is determined by PL when PRF exceeds CPRF.The SCD decreases along with increasing PL under the influence of the long PL (＞100 μs) and is un-evenly distribution during the exposure time.The SCD has no obvious correlation with PRF when PRF exceeds CPRF and is evenly distribution during the exposure time under the influence of the short PL (﹤50 μs).Our results give a further explanation of the cavitation characteristics of flowing SonoVue microbubbles mediated by PL and PRF,and have important reference significance for clinical diseases therapies.