High-Resolution Tissue Doppler and Strain Imaging for Adult Zebrafish Myocardial Tissue Through Ultrafast High-Frequency Ultrasound Vector Doppler Estimation

Zebrafish has been considered as an essential small-animal model for investigating the mechanism of heart regeneration. Due to the small size of zebrafish heart, high-frequency ultrasound (HFUS) imaging is often required for in vivo evaluations of its dynamic functions. Although commercial HFUS systems are available for myocardial velocity and strain measurement, only the outer myocardial region can be quantified due to the complex structure of zebrafish heart. In this study, a high-resolution 2-D myocardial tissue Doppler and strain imaging based on ultrafast HFUS imaging was developed for zebrafish heart imaging during heart regeneration. The cardiac flow region was first extracted to recognize the myocardial region, and the myocardial velocity and strain were then determined through vector Doppler estimation. Adult AB-line zebrafish was used for in vivo experiments, and cryoinjury was induced in the apical region of the heart. Both the myocardial velocity and strain of the whole ventricle after cryoinjury were directly visualized over 28 days. Myocardial velocity (during later diastolic motion) and strain, respectively, were significantly decreased (anterior wall: −2.0 mm/s and −3.3%; apical region: −2.0 mm/s and −4.5%; and posterior wall (PW): −1.7 mm/s and −4.3%) at the first three days after cryoinjury, which indicates weak myocardial beating due to heart injury. However, these all returned to the baseline values at 14 days after cryoinjury. All of the experimental results indicate that the proposed method is a useful tool for heart regeneration studies in adult zebrafish. In particular, it allows for the noninvasive evaluation of regional dynamic heart function.