Contrast-agent-free visualization of murine embryo-placental vasculature with ultrafast plane-wave ultrasound

In vivo assessment of the embryonic mouse placenta and vasculature is challenging, and ultrasound remains the most commonly used imaging modality. However, even with contrast agents, conventional preclinical ultrasound lacks the temporal resolution required to resolve complex vascular networks. Ultrafast Doppler methods offer a contrast-agent-free approach for visualizing embryonic placental and vascular flow.

A 15-MHz linear array was used to acquire 0.5 sec of ultrafast ultrasound data at mouse embryonic day 13.5 (E13.5) using a semi-invasive, non-destructive preparation in which a single embryo within the uterine horn was imaged in vivo. Adjacent image planes were acquired at 0.25-mm spacing to generate a 3D dataset. The data were post-processed to produce power Doppler, color Doppler, and Doppler waveforms. Image data were also segmented to facilitate visualization of distinct organ systems, including the feto-placental vascular tree.

Ultrafast Doppler ultrasound provided greater detail of vascular flow than a 30-MHz preclinical ultrasound system. Power Doppler maps delineated the feto-placental vascular tree and the umbilical, vitelline, and yolk sac circulations. Color Doppler enabled visualization of pulsatile flow over nearly two cardiac cycles in vessels such as the vitelline artery. Following segmentation, flow within the aorta, heart, placental labyrinth, and umbilical vessels could be clearly distinguished.

Ultrafast Doppler ultrasound enables in vivo contrast-agent-free visualization of embryonic feto-placental circulation in the mouse. The method provides high-resolution vascular structural and dynamic flow information across the placenta, embryo, and uterus. This approach is well suited for longitudinal studies of embryonic and placental development.