Noninvasive ultrasonic interruption of contrast agents for monitoring flow in hepatic vasculature

Abstract

An experimental setup has been designed to assess differential liver perfusion due to the hepatic artery (HA) and the portal vein (PV) using continuous intravenous infusion of ultrasound contrast agents (CA) and transcutaneous ultrasound applied to target selected vessels. A perfluorocarbon-based CA was continuously infused intravenously in the ear vein of New Zealand White rabbits. A 1-in.-diam single element medical ultrasound transducer was applied transcutaneously to interrupt the CA in the abdominal aorta. Real-time feedback from the ultrasound scanner showing the clearing of CA in the target vessel indicated successful positioning of the interruption transducer. The clearing of all CA from the hepatic vasculature was accomplished by a sufficiently long pulsed insonification of the interruption transducer. The interruption transducer was turned off, producing a sharp bolus of CA. Rapid bolus rise times on the order of 0.1 s were observed in the abdominal aorta. Sharp demarcations in vascular response between the HA and PV to the applied CA bolus was observed. Differential arrival times of the bolus between the HA and PV on the order of 7 s was measured by analysis of spectral Doppler images. Through this technique, liver perfusion due to HA and PV may be discriminated.