Fig. 1. Schematic of the system and photograph of the devices. (a) Schematic of the system: POL, plan objective lens; AMP, amplifier; DAQ, data acquisition system. (b) Schematic of the laser emission and PA signals reception. (c) Photograph of the integrated transducer.

Fig. 2. Performance of the transducer and system. (a) The echo signal detected by the transducer. (b) Bandwidth of the transducer elements with a −6  dB bandwidth of 95%. (c) The axial resolution of the system. (d) The lateral resolution of the system.

Fig. 3. Comparison of PA images experiencing pre- and post-frozen treatment with histological images. (a) The PA cross-section image of No. 2 vessel before frozen treatment. (b) The PA cross-section image of No. 2 vessel as shown in (a) after frozen treatment. (c) The matched histological cross-section image of No. 2 vessel in (a) and (b). LRC, lipid relative concentration.

Fig. 4. Comparison of PA images experiencing pre- and post-formaldehyde treatment with histological images. (a) The PA cross-section image of No. 5 vessel before formaldehyde treatment. (b) The PA cross-section image of No. 5 vessel as shown in (a) after formaldehyde treatment. (c) The matched histological cross-section image of No. 5 vessel in (a) and (b).

Fig. 5. Statistical analysis results. (a) Correlation between LR by histology and PAI post-frozen treatment, R2=0.942. (b) Correlation between LR by histology and PAI post-formaldehyde treatment, R2=0.551.

Table 1. Difference and Correlation of Lipid Ratio Derived by PAI Pre- and Post-Treatments

Table 2. Correlation of Lipid Ratio Derived by PAI and Histology Pre- and Post-Treatments

Table 3. Difference and Correlation of Lipid Ratio Derived by PAI and Histology Post-Frozen and Formaldehyde Treatment