Fig. 1. Principle of photoacoustic imaging

Fig. 2. Photoacoustic imaging systems. (a) Transmission-mode OR-PAM system; (b) reflection-mode OR-PAM system; (c) AR-PAM system with dark-field illumination; (d) PACT system with ring-shaped UTA; (e) PACT system with linear UTA; (f) PACT system with hemispherically shaped UTA; (g) PACT system based on 2D Fabry-Perot interferometer acoustic sensor; (h) side-viewing intravascular PA catheter[46]

Fig. 3. Photoacoustic imaging of breast tumor[30]. (a) UV-PAM image of fixed, unprocessed breast tumor; (b) H&E-stained histologic image of same area shown in Fig. (a) acquired after sectioning and staining breast tissue; (c)(d) zoomed UV-PAM and H&E-stained images of red dashed regions in Fig. (a) and (b), respectively; (e)(f) zoomed UV-PAM and H&E images of yellow dashed regions in Fig. (a) and (b), respectively; (g) zoomed UV-PAM image of orange dashed region in Fig. (a)

Fig. 4. Absorption spectra of hemoglobin[83]

Fig. 5. Oxygenation levels within tumor using photoacoustic imaging. (a) Two single-wavelength PAR amplitude technique; (b) two-wavelength differential PAR amplitude technique; (c) two single-wavelength phase-filtered differential PAR technique; (d) two-wavelength phase-filtered differential PAR technique[80]

Fig. 6. Photoacoustic viscoelastic imaging of tumor. (a) Optical absorption image of tumor; (b) viscoelasticity image of tumor; (c) averaged amplitude and phase delay of PA signal from marked tumor region and normal tissue [91]

Fig. 7. Photoacoustic power spectral imaging of prostate tumors[100]. (a) Ultrasonic imaging in region of interests for tumor and normal tissue; (b) mid-band fitting result after superposition of PA image and ultrasonic image; (c) slope after superposition of PA image and ultrasonic image; (d) intercept after superposition of PA image and ultrasonic image