Attenuation deforms time-intensity curves during contrast echocardiography: implications for assessment of mean transit rates.

Abstract

The mean transit rate of microbubbles of air obtained from time-intensity curves during contrast echocardiography can be used to evaluate flow through a vascular system, provided the volume of distribution of the system remains constant. We hypothesized that attenuation commonly associated with contrast echocardiography distorts the time-intensity curves, producing an error in the estimation of the mean transit rate of the microbubbles. The purpose of this study was to characterize this distortion with computer simulations and to study the effect of attenuation on the estimation of mean transit rate in an in vitro experiment. We also sought to determine if removing the data points from the time-intensity plots that visually can be attributed to attenuation before curve fitting can minimize the error in the estimation of mean microbubble transit rate. In both computer simulations and experimentally acquired in vitro data, attenuation distorted the time-intensity curves, producing an underestimation of mean microbubble transit rates. The mean microbubble transit rate decreased with an increase in microbubble concentration. Removing the points that visually were attributed to attenuation before curve fitting did not correct this error completely in the computer-simulated data and failed to correct it at all in the experimental data. These results have major practical implications in assessing mean microbubble transit rates during contrast echocardiography.