超声脉冲长度与重复频率对流动微泡群稳态空化特性的影响

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

为了深入理解超声脉冲长度(PL)与重复频率(PRF)对流动微泡群稳态空化特性的影响,本研究自行制备仿体血管,利用注射泵推动微泡群在其中恒速流动,使用1 MHz的聚焦换能器激励微泡群产生稳态空化,另一个7.5 MHz的平面换能器接收声信号,经前置放大及高速采集后送至上位机存储。在定义临界重复频率(Critical PRF,CPRF)的基础上,通过深入的时频域分析,我们发现PL和PRF共同决定流动微泡群的稳态空化特性:当PRF低于CPRF时,流动微泡群的稳态空化剂量(Stable Cavitation Dose,SCD)与PL呈正相关,且时域分布均匀;而当PRF大于CPRF时,其稳态空化特性由PL决定,在长PL (> 100μs)下,SCD随着PL增加逐渐减小,且时域分布不均匀;在短PL (<50μs)下,SCD和PRF无显著相关关系,且时域分布均匀。本研究结果深入阐明了流动微泡群的稳态空化特性,期望可用其获取可预测可控的生物效应,并应用于相关临床治疗。

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.