We present a technique called photoacoustic vector-flow (PAVF) to quantify the speed and direction of flowing optical absorbers at each pixel from acoustic-resolution PA images. By varying the receiving angle at each pixel in post-processing, we obtain multiple estimates of the phase difference between consecutive frames. These are used to solve the overdetermined photoacoustic Doppler equation with a least-squares approach to estimate a velocity vector at each pixel. This technique is tested in bench-top experiments and compared to simultaneous pulse-echo ultrasound vector-flow (USVF) on whole rat blood at speeds on the order of 1 mm/s. Unlike USVF, PAVF can detect flow without stationary clutter filtering in this experiment, although the velocity estimates are highly underestimated. When applying spatio-temporal singular value decomposition clutter filtering, the flow speed can be accurately estimated with an error of 16.8% for USVF and 8.9% for PAVF for an average flow speed of 2.5 mm/s.

中文翻译：

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利用光声和脉冲回波超声对缓慢移动的离体血液进行矢量流成像

我们提出了一种称为光声矢量流 (PAVF) 的技术，用于量化声分辨率 PA 图像中每个像素处流动光吸收体的速度和方向。通过在后处理中改变每个像素的接收角度，我们获得了连续帧之间相位差的多个估计。这些用于通过最小二乘法求解超定光声多普勒方程，以估计每个像素处的速度矢量。该技术在台式实验中进行了测试，并与以 1 毫米/秒的速度对大鼠全血进行同步脉冲回波超声矢量流 (USVF) 进行比较。与 USVF 不同，PAVF 在本实验中无需静态杂波过滤即可检测流量，尽管速度估计值被严重低估。当应用时空奇异值分解杂波滤波时，可以准确估计流速，平均流速为2.5 mm/s时，USVF的误差为16.8%，PAVF的误差为8.9%。