Cardiac parameters analysis for zebrafish heart regeneration based on high frequency ultrasound imaging

Zebrafish can fully regenerate their myocardium after up to 20% ventricular resection within 2 months without evidence of scar tissues. The extraordinary regenerative abilities provide a significant model system to study the activation of the regenerative potential of human heart tissue. In order to characterize cardiac functions of zebrafish during heart regeneration, we used high-frame-rate high-frequency ultrasound system with the capabilities of 75 MHz B-mode imaging to monitor real-time cardiac parameters. Longitudinal in vivo experiments was carried out to capture echocardiographic images from individual fishes. A pilot study on 6 fish over 30 days post amputation (dpa) was performed using this technique. A total of over 400 videos were captured. To process the large video data, an automatic image segmentation algorithm was developed. By using information obtained from temporal decorrelation of the B-mode image sequence, the epicardium is determined in a region-based level set framework combined with shape priors and Kalman filtering. Afterwards, the size of the heart was estimated frame by frame using the outlined epicardium to obtain its dynamic variation. Subsequently, the maximum and minimum of the heart size was used to calculate ejection fraction (EF). The time course of the mean EF (n=6) with a "V" shape indicates the strong ability of zebrafish to recovery cardiac functions along its morphological regeneration.