Vascular Effects Of Microbubble-enhanced Ultrasound On Muscle, Lung And Kidney Of Rabbit

BackgroundAcoustic cavitation is a major physical effects of ultrasound (US). Under certain USexcitation, microbubble in liquid is irritated as vigorous oscillation, contraction, expansion,systole and even implosion resulting in extreme local physical phenomenon such as hightemperature, high pressure, shock wave, micro-jets and luminescence. Once microbubblecontrast agent is introduced into organism as an exogenous cavitation nuclei, it cansignificantly enhance cavitation activities and cut down cavitation threshold. Becausecirculating microbubbles are always contained into vascular lumen, vascular wall becomesthe main target for cavitation injury. Microbubble induced cavitation can producesonoporation or capillary destruction.The technology of microbubble enhanced therapeutic US has showed clinical potentialin tumor therapy, liver hemostasis and benign prostate hyperplasia ablation. Many studieshave performed on the bioeffects of microbubble enhanced diagnostic US in heart, intestineand kidney. Diagnostic US is usually operated with a pressure of2-3MPa, a low duty cycleless than0.1%and a low acoustic intensity less than0.5W/cm2, much lower than that oftherapeutic US. Therapeutic US is often operated with a duty cycle more than1%and apeak negative pressure of3-5MPa. MEUS using a therapeutic device may induce moreserious vascular effects. Therefore, in order to understand MEUS injury, we need to knowthe cavitation bioeffects of involved organs. This study is to investigate the vascularbioeffects of MEUS on skeleton muscle, lung and kidney of rabbit.Objective:1. To study the vascular effects of MEUS on skeleton muscle and lung of rabbit2understand vascular effects of microbubble-enhanced ultrasound on kidney of rabbit Materials and MethodsLaboratory instruments and reagents:1. CZ-960therapeutic US instrument: It was designed and manufactured by theMianyang Sonics Ltd. The transducer of the devied emit pulsed ultrasound at a frequency of831KHZ, and related parameters such as pulse length, pulse recurrence frequency, pausetime, peak acoustic pressure are adjustable. DCT-700therapeutic US instrument: Thetransducer of the devied emit pulsed ultrasound at a frequency of1MHZ, the peck negativepressure using3.4MPa.2. Logiq9color Doppler diagnostic ultrasound imaging system,9L probe, frequency5~9MHz, eligible to perform contrast enhanced ultrasonography (CEUS) with low MI(MI0.07). Instrument is equipped with TIC time-intensity analysis software. SiemensS2000color Doppler diagnostic ultrasound imaging system, with CPS ultrasound contrastimaging mode,9L4-frequency linear array probe, frequency7-9MHz.3Microbubbles, a formulation of lipid-encapsulated MBs with perfluoropropane gas,and played roles of both contrast agents in contrast enhanced ultrasonography (CEUS)andcavitation nuclei in the treatment. The MBs were measured to be2-10um in diameter,98%of which were less than8um. And the concentration was (4-9)×109/mL.Experimental Methods1Vascular effects of microbubble-enhanced ultrasound on muscle and lung of rabbitLeg muscle and right lung of15New Zealand rabbits were treated5min using apulsed therapeutic ultrasound device (CZ-960) with intravenous injection of lipidmicrobubble. The muscles and right lungs of five rabbits were harvested for pathologicalexamination immediately after treatment. Contrast enhanced ultrasound (CEUS) wasperformed before and after MEUS treatment at post0min,30min,60min and48h in therest10rabbits. Contrast peak intensity (PI) was quantified to assess the muscle bloodperfusion. The muscles and right lungs were collected for pathological examination after48h.2Vascular effects of microbubble-enhanced ultrasound on kidney of rabbitKidney of10New Zealand rabbits were treated5min using a pulsed therapeuticultrasound device (DCT-700) with intravenous injection of lipid microbubble. Kidney of two rabbits were harvested for pathological examination immediately after treatment.Contrast enhanced ultrasound (CEUS) was performed before and after MEUS treatment atpost0min,30min,60min and48h in the rest8rabbits. Contrast peak intensity (PI) werequantified to assess renal perfusion.Results1. Vascular effects of microbubble-enhanced ultrasound on muscle and lung of rabbitPetechial haemorrhage occurred on the surfaces of treated gross muscles and lungimmediately after MEUS treatment. No significant CEUS PI difference of muscle wasfound before and after treatment. We found microvascular rupture in the form of focalhemorrhage and edema in muscle and lung.48h later, most focal hemorrhage and edemadisappeared and were replaced by minute focal necrosis in muscle.2. Vascular effects of microbubble-enhanced ultrasound on kidney of rabbitRenal blood perfusion dropped significantly after treatment, consistent to the PIdecline from (39.4±8.5) to (26.7±5.5)(p<0.05). The perfusion slowly recovered from30-60minand increased significantly after48hours treatment with the PI elevation to(42.0±9.6). We found significant glomerulus and renal tubular hemorrhage with swellingrenal tubular epithelia under light microscope.Conclusions1. MEUS can induce focal and regional microvascular rupture in muscle and lungtissues with no significant impact on muscular blood perfusion.2. MEUS can induce temporary decline of renal blood perfusion in rabbits and makedamages to renal microvessels.