Fig. 1. Schematics of dual-sided illumination photoacoustic (PA) microscopy imaging system. (a) Schematic of imaging system；(b) structure schematic of imaging head

Fig. 2. Schematics of imaging different parts of complex biological samples by different illumination modes. (a)(c) Single-sided illumination; (b)(d) dual-sided illumination

Fig. 3. Imaging results of two phantoms under different illumination modes. (a) Photo of phantom 1; (b) PA MAP of phantom 1 with single-sided illumination; (c) PA MAP of phantom 1 with dual-sided illumination; (d) quantitative results of photoacoustic signal of phantom 1 under two illumination modes; (e) photo of phantom 2; (f) PA MAP of phantom 2 with single-sided illumination; (g) PA MAP of phantom 2 with dual-sided illumination; (h) quantitative results of photoacoustic signal of phantom 2 under two illumination modes (red line：dual-sided illumination; blue line: single-sided illumination)

Fig. 4. Imaging results of leg lymph nodes in healthy mouse under different illumination modes. (a) Photo of mouse leg; (b) photo of ICG stained lymph nodes; (c) PA MAP of mouse leg lymph nodes with single-sided illumination; (d) PA B-scan image of mouse leg lymph nodes with single-sided illumination; (e) PA MAP of mouse leg lymph nodes with dual-sided illumination; (f) PA B-scan image of mouse leg lymph nodes with dual-sided illumination; (g) amplitude of photoacoustic signal intensity along red dotted line in Figs. 4(c) and 4(e), where red line represents dual-sided illumination and blue line represents single-sided illumination

Fig. 5. Label free imaging results of brain vessels of a healthy mouse with different illustration modes. (a) PA MAP image of brain vessels of a healthy mouse with dual-sided illumination; (b) enlarged box area in Fig. 5 (a); (c) PA B-scan image of dotted line in Fig. 5 (a); (d) PA MAP image of brain vessels of a healthy mouse with single-sided illumination; (e) enlarged box area in Fig. 5 (d); (f) PA B-scan image of dotted line in Fig. 5 (d); (g) amplitude of photoacoustic signal intensity with different illumination modes, where red line represents dual-sided illumination and blue line represents single-sided illumination

Fig. 6. Label free imaging results of mouse tumor area with different illustration modes (green arrow: tumor nourishing blood vessel; yellow arrow: tumor edge). (a) PA MAP image of mouse basal tumor vessels with single-sided illumination (the dotted circle is tumor area); (b) PA MAP image of mouse basal tumor vessels with dual-sided illumination; (c) PA MAP and B-scan images of mouse tumor area with single-sided illumination; (d) three-dimensional reconstruction result of Fig. 6(c); (e) PA MAP and B-scan images of mouse tumor area with dual-sided illumination; (f) three-dimensional reconstruction result of Fig. 6(e)