Bolus versus continuous infusion of microbubble contrast agent for liver ultrasound by using an automatic power injector in humans: A pilot study

Purpose. To evaluate the feasibility of using continuous infusion, in comparison with bolus injection, of a sulfur hexafluoride–microbubble contrast agent to prolong the duration of hepatic parenchymal enhancement in humans during sonographic examination. Methods. This pilot study was approved by our institution’s ethics committee. Ten patients (5 men and 5 women; mean age 6 SD, 65 6 10 years) each received two injections: a bolus injection (2 ml/s) and then continuous infusion (0.5 ml/min) of the contrast agent by using an automatic injector. Acquired cine clips were transferred to a personal computer, and the video intensity was quantified by dedicated software. Results. From the time of the first microbubble visualization in the scanning plane, maximal enhancement was reached in 6.3 6 0.94 seconds after bolus injection and in 13.9 6 1.44 seconds during continuous infusion (p 5 0.002, Wilcoxon’s test for paired data). Compared with bolus injection, continuous infusion prolonged the duration of contrast enhancement (4.3 minutes 6 42 seconds versus 7.3 minutes 6 40 seconds; p 5 0.002), although no statistically significant difference in maximal enhancement was observed (45 6 18% for bolus injection and 396 6%for continuous infusion; p50.62). Conclusions. Continuous infusion of sulfur hexafluoride–filled microbubbles via an automatic power injector prolongs hepatic contrast enhancement without significantly modifying the maximal enhancement over that at baseline. These data, coming from a pilot study, can be used to design a larger study with adequate statistical power.