Fig. 1. (a) Acoustic-resolutionphotoacoustic microscopy[1]; (b) optical-resolution photoacoustic microscopy[7]; (c) super-resolution photoacoustic microscopy[8]; (d) hollow-focused ultrasonic transducer based photoacoustic microscopy[11]

Fig. 2. (a) Photoacoustic image of blood vessel; (b) image of oxygen saturation; (c)(d) images of blood velocity[31]

Fig. 3. Photoacoustic viscoelasticity images of (a) phantoms containing various concentrations of lipid and (b) atherosclerotic plaque sample[35]

Fig. 4. Photoacoustic images of (a) cell nuclei, (b) red blood cells, (c) retinal vessels and retinal pigment epithelium layer, (d) microvasculature enhanced by Evans blue dye, (e) B16 melanoma labeled with targeted gold nanocages, (f) tumor expressed by near-infrared fluorescent protein iRFP[37]

Fig. 5. (a) Fabry-Perot polymer film etalon ultrasound sensor based photoacoustic imaging system[45]; (b) polymer microring resonators based photoacoustic imaging system[58]; (c) low coherence Michelson interferometer based photoacoustic imaging system[63]

Fig. 6. In vivo imaging of mouse ear using multi-modal imaging system[70]. Images of (a) AOPAM maximum amplitude projection, (b) OCT maximum amplitude projection, and (c) FLM maximum amplitude projection; (d) image fused AOPAM, OCT and FLM; (e) AOPAM, OCT and fused AOPAM-OCT B-scan images of white dotted line 1 in (a); (f) AOPAM, OCT and fused AOPAM-OCT B-scan images of white dotted line 2 in (a); inset in (c) is fluorescence image of mouse ears obtained under a stereomicroscope

Fig. 7. (a) Schematic of virtual-detector concept; (b) illustration of coherent factor weighting[75]

Fig. 8. Photoacoustic images of (a) mouse ear vasculature[7] and (b) mouse brain vasculature and oxygen saturation[84]

Fig. 9. In vivo imaging results by all-optical photoacoustic (AOPA) and OCT system. AOPA maximum amplitude projection images of (a) normal, (b) BCC, and (c) MM mouse ear; (d)-(f) OCT B-scan images for white dotted line in (a)-(c); (g)-(i) imaging with H&E staining histopathology[71]

Fig. 10. (a) Scanning head of portable photoacoustic mesoscopy; photoacoustic image of (b) psoriatic skin and (c) normal skin[103]