Schematics of (a) OR-PAM system and (b) AR-PAM system.

Photoacoustic microscopy of tissue phantoms with different pH values. (a) Photograph of the tube phantom for OR-PAM with overlaid mouse skin tissue Scalebar: 2 mm. (b) Averaged cross-sectional OR-PAM image of three tubes along the black dotted line in (a). The overlaid mouse skin is ∼200 μm thick Scalebar: 0.1 mm. (c) Photograph of the multiwell tissue phantom for AR-PAM with overlaid chicken breast tissue Scalebar: 4 mm. (d) Averaged cross-sectional AR-PAM image of two wells along the black dotted line in (c). The thickness of breast tissue varied from 1.4 to 2.0 mm Scalebar: 0.5 mm.

pH images from OR- and AR-PAM. (a) OR-PAM pH image of three tubes filled with 0.1 mM SNARF solutions with pH of 7.78, 6.78, and 7.45, respectively. (b) OR-PAM pH image of the same phantom with overlaid mouse skin tissue. Scale bar: 1 mm. (c) AR-PAM pH image of four 3-mm diameter wells filled with 0.1 mM SNARF solutions with pH of 7.78, 6.78, and 7.45, respectively. (d) AR-PAM pH image with overlaid chicken breast tissue. Scale bar: 3 mm. (e) Quantitative comparison of pH measurements from pH meter with those from OR- and AR-PAM with and without tissue overlay. The data was shown in mean ± SD. NT: without tissue overlay; WT: with tissue overlay. The correlation coefficients (R value) between the pH meter reading and the measurements from OR_NT, OR_WT, AR_NT, and AR_WT were all greater than 0.95 and agree with p-values less than 0.05. (f) Normalized mean absorbance at 580 nm of 0.1 mM SNARF buffer solutions with pH 6.78, 7.45, and 7.8 after 1, 5, and 10 PA imaging experiments.