Accuracy and reproducibility of coronary flow rate assessment by real-timecontrast echocardiography: In vitro and in vivo studies

Real-time myocardial contrast echo (MCE) provides the potential to assess m yocardial blood flow from time-intensity refilling curves after high-energy bubble destruction. This study validated the accuracy of this approach and the effect of specific examination variables and instrument settings on re sults. The effects of examination depth and angle as well as dynamic range, pulse repetition frequency, and line density were assessed with the use of in vitro incremental flow rates produced in an in vitro tissue phantom. In vivo recordings of real-time imaging with an infusion of a contrast agent (Optison) were obtained in 7 open-chest dogs with graded left anterior desc ending artery stenosis at baseline and during adenosine hyperemia, and were compared with flow probe measurements. After bubble destruction, time-inte nsity data were fitted to an exponential function, and the rate of intensit y increase (b) and peak plateau intensity (A) were derived from refilling c urves. In vivo real-time values for b, but not A, correlated closely with f low probe measures (r = 0.93). A similar correlation for b was observed in vitro (r = 0.98). The correlation between flow rate and b was influenced by several examination variables, including depth, angle, and instrument sett ings. Real-time MCE provides accurate quantification of coronary flow by as sessing the rate of microbubble refilling. However, this parameter may be a ffected by several examination and instrument variables. Therefore, real-ti me MCE refilling measures are best applied by comparing baseline values wit h those of stress studies.