In vivo Visualization of Vasculature in Adult Zebrafish by High Frequency Ultrafast Ultrasound Imaging

Objective: Zebrafish has been recently considered an ideal vertebrate for studying developmental biology, genetics, particularly for modeling tumorigenesis, angiogenesis, and regeneration in vivo. However, when a zebrafish matures completely, its body loses transparency, thus making conventional optical imaging techniques difficult for imaging internal anatomy and vasculature. Acoustic wave penetration outperforms optical methods, high-frequency (>30 MHz) ultrasound (HFUS) was consequently an alternative imaging modality for adult zebrafish imaging, particularly for echocardiography However, visualizing peripheral vessels in a zebrafish by using conventional HFUS is still difficult. Methods: In the present study, high-frequency micro-Doppler imaging (HF-DI) based on ultrafast ultrasound imaging was proposed for zebrafish dorsal vascular mapping in vivo. HF-DI used a 40-MHz ultrasound transducer, which is an ultrafast ultrasound imaging technology with the highest frequency available currently. Blood flow signals were extracted using an eigen-based clutter filter with different settings. Experiments were performed on an 8-month-old wild-type AB-line adult zebrafish. Results: Blood vessels, including intersegmental vessels, parachordal vessel, dorsal longitudinal anastomotic vessel, and dorsal aorta, from the dorsal side of the zebrafish were clearly observed in two-dimensional (2D) and three-dimensional (3D) HF-DI. Conclusion: The maximum image depth of HF-DI and the minimal vessel diameter can be detected were 4 mm and 36 μm, respectively; they were determined without any use of microbubbles. The maximum flow velocity range was approximately 3-4 mm/s on the dorsal vessels of the adult zebrafish. Significance: Compared with conventional ultrasound Doppler imaging, HF-DI exhibited superior small vessel imaging