Fig. 3

Specificity evaluation of the probe in vivo and ex vivo. T2-weighted MR imaging of tumor before and 0.5, 1, 2, 4, 6, and 24 h after intravenous injection of ¹⁹F-RGD@USPIO (A) or nontargeted ¹⁹F-PDA@USPIO (B). C Time-activity curves of T2 relaxation time of tumors before and after probe injection. Error bars denote standard errors, Mann–Whitney U-test were applied, *P < 0.05. D Prussian blue iron staining, CD31 vascular staining, and F4/80 macrophage staining were performed in consecutive sections: (antigen-positive area are brown and USPIO-positive area are blue: see arrows). While ¹⁸F-RGD@USPIO and ¹⁸F-PDA@USPIO both accumulate within tumors, the ¹⁸F-PDA@USPIO do so mainly through association with macrophages rather than microvasculature. Magnification: × 200