Estimating both direction and magnitude of flow velocity using photoacoustic microscopy

This report studies absolute estimation of both the direction and magnitude of flow velocity, at microscopic scale, with acoustic resolution photoacoustic microscopy. Fundamentally, it is based on the quantitative measurement of Doppler frequency shift in the short laser pulse induced photoacoustic (ultrasound) signals. Experiments were carried out in a transparent plastic tube through which light absorbing liquid solution (as imaging target) flows. We investigated various cases of flow velocity: (i) variation in direction (0°–90°) and (ii) variation in magnitude (0.5–5 mm/s). This study demonstrates simultaneous recovery of both direction and magnitude from a set of data noninvasively and nondestructively.