Complete Bubble Destruction is Essential for Quantitative Assessment From the Replenishment Curve in Real-time Myocardial Contrast Echocardiography

Background. Myocardial perfusion can be quantified using the replenishment curve of the myocardial opacification derived after transient high power ultrasound exposure (burst) in real-time myocardial contrast echocardiography (MCE). However, the effect of acoustic power of burst for bubble destruction may confound results. Thus, the goal of the present study was to examine the effect of burst intensity on the parameters of the replenishment curve. Methods. Myocardial opacification of the left ventricular short-axis view was observed using SIEMENS Sequoia 512 (mechanical index = 0.1) during infusion of Definity in eight open-chest dogs. The mechanical index (MI) of burst was set as high and low (0 and -11dB), and the regions of interest were placed on the anterior and lateral walls of the left ventricle. The temporal changes in video intensity of the end-diastolic phase after the burst procedure were fitted to an exponential function: y=a(1-e-βt)+c. The plateau video intensity was defined as the A-value which was calculated as the sum of the a and c values.Results. The A-value remained constant with changes in the burst MI. Although the video intensity after the high intensity (0dB) burst was similar to that of the baseline, the video intensity after the low intensity (-11dB) burst was significantly higher than that of the baseline (anterior: 5.5±2.2 dB at baseline vs. 7.4±2.4 dB at -11dB burst; lateral: 5.9±2.5 dB at baseline vs. 9.3±3.2 dB at -11dB burst), which suggests that low MI burst results in incomplete bubble destruction. Furthermore, the β-value increased as the burst MI decreased (anterior: 0.39±0.07 and 0.54±0.15; lateral: 0.27±0.05 and 0.39±0.12 in response to a burst MI of 0 and -11dB, respectively).Conclusions. The myocardial microbubble velocity (β-value) derived from the replenishment curve by using bubble destruction technique in real-time MCE is overestimated when bubble destruction is incomplete.