The Effect of Inhaled Gases on Ultrasound Contrast Agent Longevity In Vivo

PURPOSE: The purpose of this study is to investigate the effect of the inhaled gas used alongside isoflurane in the anesthetization of small animals on the time-intensity curves (TICs) acquired from ultrasound contrast agents—microbubbles. PROCEDURES: TICs were recorded over the common iliac vein of 12 mice receiving Definity®. Animals were anesthetized with isoflurane, the ventilator was driven by medical air (MA), then in random order, the driving gas was changed for 3 min to: MA (control); pure oxygen (O(2)); O(2) + perfluorohexane (PFH:O(2)); or O(2) + octafluoropropane (OFP:O(2)), the perfluorocarbon (PFC) in Definity, followed by a return to MA 3 min later. RESULTS: The mean slope of signal decay was −0.47, −1.05, −1.16, and −1.42 video-intensity units/s for MA, OFP:O(2), PFH:O(2), and O(2), respectively; MA had the slowest decay (p < 0.0001). Both PFC mixtures had slower signal decay than O(2), but only OFP:O(2) was significant (p < 0.01). When MA was used immediately following dosing, slope gradually decreased (p = 0.032) and was two times slower by the fourth injection (p = 0.012). CONCLUSIONS: Microbubble kinetics are closely associated with the driving gas for inhaled anesthesia. MA has the least effect and should be used when inhaled anesthesia is used. Furthermore, when animals are given multiple injections in the same session, microbubbles last longer with subsequent injections.