An in-vivo evaluation of the effects of anesthesia carrier gases on ultrasound contrast agent circulation

Both clinical and preclinical ultrasound imaging studies use microbubble contrast agents. Short in-vivo lifetimes limit the diagnostic and therapeutic capabilities of these contrast agents, and currently there is research interest in how to lengthen their circulation times. Differences have been observed in contrast agent circulation times during preclinical studies depending on the type of inhaled anesthesia carrier gas. This paper presents the observations from a controlled experiment that evaluated differences in circulation times for lipid shelled perfluorocarbon-filled contrast agents circulating in rodents as a function of inhaled anesthesia carrier gas. Both pure oxygen and medical air are considered and we discuss the persistence of the contrast agents as determined by ultrasound video intensity. The results show a significantly longer in-vivo contrast agent circulation for animals breathing medical air as compared to breathing pure oxygen. Simulations show enhanced contrast persistence may be explained by classical diffusion and that nitrogen plays a critical role by contributing to the volume and diluting the other gas species in the microbubble gas core.