A Novel Method for Quantitative Myocardial Contrast Echocardiography in Mice

The small size of the mouse heart frequently imparts technical challenges when applying conventional in vivo imaging methods for assessing heart function. Here we describe the use of high frequency ultrasound imaging in conjunction with a size-tuned blood pool contrast agent for quantitatively assessing myocardial perfusion in living mice. A perflurocarbon microbubble formulation exhibiting a narrow size distribution was developed, and echogenicity assessed at 18 MHz in vitro. Adult mice were subjected to permanent ligation of the left anterior descending artery. Ultrasound imaging was performed on day 7, and a cohort of intact mice was used as a control. Parasternal long axis cine clips were acquired at 18 MHz before and after contrast administration. Reduced ejection fraction and increased end systolic volume was observed in infarcted compared to control mice. In control animals wash-in of the contrast agent was visible in all myocardial segments. Reduced contrast enhancement was observed in apical-posteriolateral regions of all infarcted mice. A novel method for re-slicing of the imaging data through the time domain provided a two-dimensional presentation of regional contrast agent wash-in, enabling convenient identification of locations exhibiting altered perfusion. Myocardial segments exhibiting diminished contractility were observed to have correspondingly low relative myocardial perfusion. The contrast agent formulation and methods demonstrated here provide the basis for simplifying routine in vivo estimation of infarct size in mice, and may be particularly useful in longitudinal evaluation of revascularization interventions and assessment of peri-infarct ischemia.