Purpose: To investigate whether continuous infusion of an echo-enhancing contrast agent for up to 15 minutes can provide uniform and prolonged enhancement.
Materials and methods: Six volunteers each received one bolus and three infusions of a microbubble contrast agent over 6-15 minutes at (a) a standard rate (mean, 2.08 mL/min), (b) a fast rate at twice the standard rate, and (c) a slow rate at half the standard rate. Spectral Doppler intensitometry of the femoral artery was performed for all infusions. Spectral Doppler ultrasound (US) scans of the femoral artery and color Doppler US scans of the carotid artery were subjectively assessed.
Results: All infusions provided an equilibrium plateau of constant prolonged enhancement starting after 1-2 minutes and lasting until the end of the infusion. Enhancement at the plateau was +13 dB (slow rate), +17.1 dB (standard rate), and +18.3 dB (fast rate) compared with baseline. Saturation artifacts with infusions were markedly fewer than those with bolus injections. Dose effectiveness (duration of enhancement that measured at least 7.5 dB per gram of contrast agent) was markedly improved with the infusions, from 0.8 min/g for the bolus to 2.6 min/g for the slow infusion.
Conclusion: Continuous infusion of the microbubble contrast agent provided prolonged and uniform enhancement of Doppler signals and improved image quality by minimizing saturation artifacts.