The Doppler kinetics of microbubble echo contrast.

The right and left heart kinetics of a saccharide-based microbubble echo contrast agent were measured in 11 anesthetized dogs using Doppler intensity as a measure of microbubble concentration while controlling for the dose administered, weight of the subject and cardiac output. A two-phase Doppler time-intensity curve was noted in all vascular regions. A brief first pass effect (phase 1) was found to depend on the contrast dose, cardiac output and subject size. This was followed by a much longer nearly steady-state elevation in the Doppler intensity compared with baseline (phase 2). The kinetics of phase 2 were found to be the same in all vascular distributions and independent of cardiac output. The phase 2 kinetics depend on the contrast dose, subject size and elimination characteristics of the contrast agent. The clinically important conclusions are: (1) the magnitude of Doppler enhancement and duration of the contrast effect can be predicted using the simple formulas presented; (2) the flow-dependent portion of the arterial contrast effect is effectively over only a few seconds after intravenous injection; and (3) the kinetics of phase 2 are the same throughout the body.