Three-dimensional imaging of the vasculature in chicken embryo by combination of ultrasonic and photoacoustic imaging

Vascular network is a good target for PA imaging with conventional 532 nm laser because the extinction coefficient is of red blood cell is high between 500 and 600 nm. Compared with US Doppler technique, PA imaging is superior for visualization of low speed blood flow in small vessels. Laser pulses were generated by a semiconductor diode laser with the wavelength of 532 nm, the pulse width of 3.4 ns. PA signal was received by a 50 MHz concave ultrasound transducer with a 1 mm hole in the central part to get through an optical fiber in order to concentrically align the light illumination and signal reception. Fertile chicken eggs were placed in a shallow dish after 3 days of incubation for easy observation with US and PA imaging. US imaging visualized overview of the whole body, especially, the vertebral column were clearly displayed. PA imaging visualized the heart and great vessels including aortic arch. This study showed the feasibility of US-PA combined imaging for observation of ex ovo chicken embryo and future application of the imaging modality in the developmental biology.