Experimental Study Of Ultrasound-enhanced Vascular Permeability Of Rats' Limb

Ultrasound-microbubble mediated local drug delivery has been proved to be effective for sonochemotherapy and opening blood-brain barrier.The potential mechanism is that the cavitation induced by ultrasound-microbubble can transiently enhance vascular permeability and promote drug release.In this study,arteries of SD rats' hindlimb were sonicated.SonoVue solution(3.5ml/kg)was injected into the rats in the ultrasound+SonoVue group but not into the pure ultrasound group.Then 5 min sonication treatment was conducted with therapeutic ultrasound(500 kHz central frequency,0.4 MPa peak rarefactional pressure,1 Hz pulse repetition frequency,1% duty cycle).Different time windows(2.5,5,10,20,30,60 min)were set to inject Evans blue(EB)as a stain.After dissecting the rats,intracardiac perfusion was conducted,and the effusion of EB was evaluated by direct observation,in vivo imaging and chemical detection methods.Using statistical analysis,the outcomes showed that the exudative amount of EB in the sonicated side of the ultrasound+SonoVue group(2.5-30 min)was significantly higher than that in the control group(p<0.05).And there was no significant difference of EB effusion amount in the opposite side between the ultrasound+SonoVue group and the control group.This result proved that ultrasound+SonoVue could enhance vascular permeability of rats' hindlimb and the effective time window was 2.5-30 min.In addition,the exudative amount of EB in the sonicated side of the pure ultrasound group(0,30,60 min)was significantly higher than that in the control group(p<0.05),while no significant difference of EB effusion amount in the contralateral side was detected.That indicated that vascular permeability of rats' hindlimb could be enhanced by pure ultrasound sonication to some extent as well.Since cavitation may lead to an acute inflammatory effect and other adverse consequences,in this study,a system for passive cavitation detection was established to monitor the cavitation dynamics.This system was highly integrated and the sampling rate was 60 MHz.Systematic tests were carried out including: 1)utilize oscilloscope to test the amplitude,pulse duration,frequency characteristic of the signals generated by the signal generation module;2)use the signal acquisition module to acquire the amplitude and frequency characteristic of the specific signals generated by a standard waveform generator.The results showed that this system could produce correct ultrasonic excitation signals and accurately collect and process the acoustic cavitation signals.Furthermore,the detailed process of passive cavitation detection in vitro was explored.A sonication experiment using focused ultrasound(1 MHz central frequency,0.7 MPa peak rarefactional pressure,1 kHz pulse repetition frequency,10% duty cycle)and deionized water was conducted,in which no cavitation activity was detected.