Fig. 1. Schematic diagram of blood oxygen measurement device and absorption spectrum of hemoglobin to dual-wavelength excitation light. (a) Blood oxygen measurement device based on dual-wavelength photoacoustic excitation and detection; (b) optical absorption spectra of oxygenated and deoxygenated hemoglobin, and optical spectrum of dual-wavelength pulse excitation light source

Fig. 2. Signal-to-noise ratio measurement results under same photoacoustic signal. (a) Signal-to-noise ratio of photoacoustic signal measurement varying with light intensity injected into photodetector; (b) time trace of photoacoustic signal when injected intensity is 4 mW; (c) time trace of photoacoustic signal when injected intensity is 17 mW

Fig. 3. Schematic diagram of photoacoustic functional imaging system and comparison of signal-to-noise ratios of ultrasonic sensors. (a) Structure of photoacoustic imaging probe; (b) frame diagram of photoacoustic imaging system; (c) measurement result of ultrasonic signal by diaphragm ultrasonic hydrophone; (d) measurement result of ultrasonic signal by fiber optic ultrasonic sensor

Fig. 4. Blood oxygen functional imaging results and measurement errors under different signal-to-noise ratios. (a) Spatial distribution of hemoglobin concentration and blood oxygen saturation in cerebral cortex vessels of mouse; (b) measurement error of blood oxygen saturation varying with signal-to-noise ratio of photoacoustic signal detection

Fig. 5. Photoacoustic functional imaging results.(a)-(c) Imaging results of vessels in mouse ear; (d)-(f) endoscopic imaging result of rat rectum

Fig. 6. Changes and analysis of blood oxygen in capillaries of intestinal wall of rat. (a) Spatial distribution of blood oxygen saturation in intestine of rat; (b) enlarged view of dotted box in Fig. 6(a); (c) process of blood oxygen released from capillary along direction indicated by arrow in Fig. 6(b)