Fig. 1. Structural diagrams of (a) confocal annular array transducer and (b) vibro-acoustography system[7]

Fig. 2. Structural diagram of resonant ARF-OCE system based on spectral-domain OCT system[10]

Fig. 3. Experimental setup of photoacoustic elastography system[11]

Fig. 4. Photoacoustic viscoelasticity imagings of three samples (muscle, fat and liver). (a) Photograph of sample; (b) photoacoustic viscoelasticity imaging of sample[11]

Fig. 5. Detection process of amplitude and phase of photoacoustic signal based on lock-in measurement[18]

Fig. 6. Optical absorption and viscoelasticity images of murine EMT6 tumor. (a) Optical absorption image of the tumor; (b) viscoelasticity image of the tumor; (c) photograph of the tumor; (d) averaged amplitude and phase delay of the photoacoustic signal from the marked tumor region compared to the normal tissue; (e) normal tissue and (f) tumor with hematoxylin-eosin stain[18]

Fig. 7. Schematic of QPAE system. (a) Lateral and front view of photoacoustic imaging probe; (b) QPAE system setup[24]

Fig. 8. QPAE images of the human musculus biceps in vivo at different loadings. (a) 0 kg; (b) 2.5 kg; (c) 5.0 kg; (d) 7.5 kg; (e) 10.0 kg; (f) averaged Young's modulus value in each layer as a function of load[24]

Fig. 9. (a) Photoacoustic elastography images of vertical and en-face expansion scanned by 360° in the interior of the sample; (b) photoacoustic elastography image and the corresponding histology image and phase distribution at z=0.8 mm[27]