Mesentery Vascular Damage Induced By Microbubbles Mediated Ultrasound Cavitation

Background:Noninvasive thermal ablation of tumor by high intensity focused ultrasound(HIFU) is desirable but limited in clinic by a series of side effects.Recently,microbubble(MB) ultrasound contrast agent was found to have potential in therapeutic purposes because MB can act both as a drug carrier and a cavitation nucleus.MB enhanced cavitation was able to ablate targeted tissues mechanically without thermal effect and happened at a low intensity level.Under this condition,most side effects of HIFU can be avoided.Objective:This study was tried to explore the mesentery vascular bioeffects made by MB mediated non-focused or focused ultrasound.The vascular bioeffects include endothelial damage and thrombosis.Other bioeffects factors may include MB dosage and insonation duration.In addition,fibrinogen conjugated MB was firstly tested to accelerate the clots formation.Methods:1.Occlusion of mesentery microvessels using low intensity planed therapeutic ultrasound and fibrinogen conjugated microbubblesFibrinogen conjugated MB was prepared with direct binding method.Fibrinogen viability was detected in fibrinogen conjugated MB and compared with the controlled fibrinogen solution.The intensity of therapeutic ultrasound device CSY-01 was measured by acoustic radiation method.Twenty New Zealand white rabbits were divided into four groups at random for different therapeutic combinations.The therapeutic factors included fibrinogen conjugated MB,therapeutic ultrasound(US) and fibrinogen solution.Blood flow of mesentery microvessels were examined under a stereomicroscope before and after US radiation.Evans blue dye(EB) was injected intravenously to trace the circulation.2.Injury of small mesentery arteriovenous vessels by MB mediated pulsed focused ultrasoundThe peak acoustic pressure of the focused therapeutic ultrasound device CSY-03 was measured using a hydrophone.Potential thermal effect of CSY-03,the focused device,on rabbit ear was measured by a commercial infrared thermal sensor before and after ultrasound radiation.Forty-five New Zealand white rabbits were divided into twelve groups randomly for different MB dosage,different radiation times and different MBs.The small mesentery arteriovenous vessels were carefully aimed and insonated by pulsed focused ultrasound. Hematoma around the vessels was quickly formed and measured in size.It was later sent for pathological examination.Results:There were no statistical difference of fibrinogen viability between the fibrinogen conjugated MB suspension and the primary fibrinogen solution.The output acoustic power of CSY-1 was 1.02 W and space peak temporal average intensity(I_SPTA) was 0.3 W/cm².Blood flow current of mesentery vessel was smooth and rapid before in all of the rabbits and it remained smooth and rapid after therapies in the groups of the simple fibrinogen conjugated MB,the simple therapeutic US and the fibrinogen plus therapeutic US.The mesentery microvessels were blocked in the group of fibrinogen conjugated MB plus therapeutic US.EB staining was found in all of mesentery sectors except the insonated territory of the last group,which remained red.Peak acoustic pressure of CSY-3,the focused therapeutic device was 1.0 MPa.There were no temperature changes of rabbit ears before and after focused ultrasound radiation.Hematoma happened around the mesentery vessels in almost all the experimental groups with intravenous injection of MB and it grew with increased MB doses.In the pathology of hematoma,severe red blood cell(RBC) extrusion out of vessel,side adhesion, endothelial malformation and discontinuity or rupture of vessel wall could be observed.Conclusions:Fibrinogen remained vital after conjugated with lipid microbubble.The mesentery microvessels can be blocked by ultrasound insonation coordinated with fibrinogen binded MB.Thermal effect of pulsed focused ultrasound was minimal and could be neglected.When coordinated with MB,pulsed focused ultrasound at a low intensity level could rupture or damage small mesentery vessels,resulted in exudation of blood content,vessel thrombosis.This bioeffect was related to MB doses,but not related to insonation duration.