Fig. 1. Schematic of photoacoustic imaging ^［21］

Fig. 2. Schematic diagram of photoacoustic computed tomography^［27］

Fig. 3. Traditional PACT imaging system with unitary ultrasound transducer^［28］

Fig. 4. High-frequency full-field linear array PACT imaging system ^［29］

Fig. 5. Single-pulse panoramic PACT imaging system^［30］

Fig. 6. Different PACT systems for human breast cancer detection^［35-36］

Fig. 7. Comparison of OR-PAM and AR-PAM imaging principles^［27］

Fig. 8. Diagram of the second generation OR-PAM system designed by WANG L V's group^［50］

Fig. 9. Imaging results of the second generation OR-PAM system on the ears of live mice^［50］

Fig. 10. Dual-wavelength optical resolution photoacoustic microscopy imaging system^［53］

Fig. 11. Schematic diagram of the three-wavelength OR-PAM imaging system^［55］

Fig. 12. Imaging of mouse ears under a three-wavelength imaging system^［55］

Fig. 13. Schematic diagram of the five-wavelength OR-PAM proposed by Lidai Wang's group ^［56］

Fig. 14. Results of imaging blood and lymphatic vessels in the mouse ear using five-wavelength OR-PAM^［56］

Fig. 15. Schematic diagram of the photoacoustic endoscopic probe ^［74］