Fig. 1. Basic principle of measuring blood flow velocity using photoacoustic thermal measurement method

Fig. 2. Schematic of photoacoustic measurement system

Fig. 3. Photoacoustic acquisition and detection module and physical image of sample chamber

Fig. 4. Schematic of scanning method of scanning motion module

Fig. 5. System control interface

Fig. 6. Photoacoustic signals during fixed single-point speed measurement. (a) Locating ultrasound signal peaks; (b) peak extraction and smoothing processing

Fig. 7. P¯(t)-v curves at different flow rates

Fig. 8. Comparison of measured speed and true speed

Fig. 9. System lateral resolution

Fig. 10. Photoacoustic imaging of copper wire. (a) Physical image of copper wire; (b) average photoacoustic pressure amplitude; (c) two-dimensional scatter plot; (d) average photoacoustic pressure amplitude surface generated after Gaussian filtering; (e) two-dimensional image of copper wire structure

Fig. 11. Morphology and speed co-measurement results. (a) Physical image of imaging area; (b) three-dimensional scatter plot of photoacoustic pressure amplitude; (c) two-dimensional scatter plot of photoacoustic pressure amplitude in cross-section of glass tube; (d) velocity distribution