2 In vivo cardiac imaging of adult zebrafish using high frequency ultrasound

The zebrafish has emerged as an excellent model organism for studies of cardiovascular development due to its optical transparency and external development during embryogenesis. However, to understand the cardiovascular structure and function beyond the early stage development requires a high-resolution, real-time, non-invasive imaging alternative due to the opacity of adult zebrafish. In this paper, we report the development of a high frequency ultrasonic system for adult zebrafish cardiac imaging, capable of 75 MHz B-mode imaging at a spatial resolution of 25 mu m and 45 MHz pulsed-wave Doppler measurement. The system allows for real-time delineation of detailed cardiac structures, estimation of cardiac dimensions, as well as image-guided Doppler blood flow measurements. In vivo imaging studies on ten one-year old zebrafish showed the identification of the detailed cardiac structures in real-time images. Doppler waveforms at various locations demonstrated the utility of this system to study zebrafish cardiovascular hemodynamics. In addition, the detection of E-flow and A-flow during the ventricular filling, and the appearance of diastolic flow reversal at bulbus arteriosus suggested the functional similarity of zebrafish heart to that of higher vertebrates.