Fig. 1. Vector distribution diagrams of absorption coefficient of traditional isotropic absorber and absorber considering actual anisotropy. (a) Traditional isotropic absorber; (b) absorber considering actual anisotropy

Fig. 2. Hand-held photoacoustic computed tomography probe with adjustable polarization angle. (a) Schematic diagram of each part of probe; (b) probe's optical, acoustic confocal, and spot size indication; (c) trapezoidal visual window and scale diagram; (d) physical diagram of probe structure

Fig. 3. Schematic diagram of polarization PACT system

Fig. 4. Polarization angle calibration of probe. (a) Probe polarization angle calibration platform; (b) 0° polarized light corresponds to parameters of polarization measuring instrument; (c) schematic diagram of polarization angle of calibration; (d) picture of sample; (e) photoacoustic imaging results excited by linearly polarized light with different polarization angles ; (f) statistical values of photoacoustic signals of samples PVA and PVC in Fig. (d) varying with light polarization angle

Fig. 5. Results of simulated experiment. (a) Photograph of samples; (b) photoacoustic imaging results of sample (a) excited by linearly polarized light with different polarization angles; (c) statistical value of photoacoustic signal of PVA and PVC in sample (a) varing with polarization angle; (d) schematic diagram of PVA at different depths in same optical axis direction; (e) photoacoustic imaging results of PVA at different depths under different polarization angles of light excitation

Fig. 6. Experimental results of biological tissues. (a) Bovine tendon imaging area and its enlarged picture; (b) photoacoustic imaging result of sample (a) excited by linearly polarized light with 0° polarization angle; (c) photoacoustic imaging result of sample (a) excited by linearly polarized light with 90° polarization angle; (d) result of photoacoustic signal subtracted from photoacoustic signal excited by the two polarization angles

Table 1. Comparison table of probe polarization angle and calibration angle