Effect of microbubble exposure to ultrasound on quantitation of myocardial perfusion

Background: The purpose of this study was to determine whether acoustic disruption of microbubbles in the left ventricular (LV) cavity prior to entry in the coronary circulation or their gradual destruction in the myocardium during myocardial contrast echocardiography (MCE) affects quantitative parameters of myocardial perfusion. Methods: MCE was performed in 12 open chest dogs with both intermittent high-power imaging (IHPI) and real-time low-power imaging (RLPI). To assess the affects of microbubble destruction in the LV cavity, MCE parameters of myocardial perfusion were compared for imaging planes that included versus avoided the LV cavity. To assess the effects of gradual disruption of microbubbles in the microcirculation during RLPI, MCE parameters from frames acquired continuously were compared to that from acquiring only end-systolic frames. Results: Destruction of microbubbles in the LV cavity did not alter perfusion data for either form of imaging unless RLPI was performed using long (6-frame) destructive pulse sequences. With RLPI, a gradual decay in microbubble signal occurred during their myocardial transit, the degree of which was related to the acoustic power. Signal decay during microbubble transit resulted in an overestimation of the microvascular blood velocity (β-value) and an underestimation of the microvascular blood volume (A-value). Conclusions: MCE parameters of perfusion at low power can be significantly altered by microbubble destruction in the LV cavity and in the myocardial microcirculation during RLPI. Short microbubble destruction pulse sequences and imaging only at end-systole can reduce these effects.