Pulsed photoacoustic flow imaging of whole blood with low frequency detection

Ultrasound flow imaging is widely used for quantification of blood flow in vivo, but estimating low flow velocities remains challenging. Pulsed photoacoustic flowmetry could be an alternative-but has not been shown capable of deep in vivo imaging so far. A new photoacoustic system is proposed, that has more potential for deep in-vivo applications. In this work the system is tested in vitro. In contrast to earlier research, 1064 nm NIR laser irradiation is used, that would allow deeper in-vivo light penetration. For detection, a 15 MHz transducer with lower in-vivo tissue ultrasound attenuation is used. Both changes are not trivial, as they reduce the overall visibility of the photoacoustic signals from red blood cells. This work shows the flow estimation performance of this system in vitro, and aims to serve as a point of reference when moving to an in-vivo application. Using this 15 MHz transducer, 1D flow profiles of flowing blood were extracted. The jitter (standard error) in the velocity estimation over the profiles was 10% when estimating flow of particles and 20% with whole blood; the bias in flow estimation was roughly 30%.