Fig. 1. Schematic of OPAM system

Fig. 2. Out-of-focus measurement mode based on sphere-focused ultrasonic detector

Fig. 3. Results of phantom experiment. (a) Photograph of phantom; (b) reconstructed result by traditional back-projection algorithm; (c) reconstructed result by modified back-projection algorithm combined with virtual point technique

Fig. 4. Profiles of three microspheres along x and y directions. (a)(d) Microsphere 1; (b)(e) microsphere 2; (c)(f) microsphere 3

Fig. 5. Photo of mouse tumor imaging

Fig. 6. Experimental results of mouse tumors. (a)--(f) OPAM imaging results of pancreas tumors; (g)--(l) OPAM imaging results of liver tumors

Fig. 7. Box-and-whisker plots of four parameters for pancreas and liver tumors, where P values are calculated by two-sample t-test, *represents P<0.05, and **represents P<0.01. (a) G_ASM; (b) G_ENT; (c) G_CON; (d) G_CORR

Fig. 8. Box-and-whisker plots of blood oxygen saturation values for pancreas and liver tumors