A) Representative PET images of U87MG tumor-bearing mice intravenously injected with 64Cu-labeled v-A-CED2 at different time points post injection. B) Drug accumulation in tumor quantified from decay-corrected PET images (n = 3). C) Photoacoustic/ultrasound co-registered images obtained at 780 nm before and 1 h, 4 h, 24 h, and 48 h after intravenous injection of CED2 and v-A-CED2 (100 uL, 0.5 mg/ml of CED2 content) in U87MG tumor-bearing mice (n = 3). D) and E) 3D PA images of tumor tissues at 1 h p.i. of CED2 and 24 h p.i. of v-A-CED2, respectively. F) Corresponding quantification of PA signals of mice tumor region before and immediately, 1 h, 4 h, 24 h, and 48 h after intravenous injection of CED2 and v-A-CED2. *P<0.05, **P<0.01.