Time–activity curves of tumor, liver, kidneys, and muscle from quantitative microPET imaging analysis of (a) the 64Cu–NOTA–FA–FI–PEG–PEI–Ac–Mn3O4 NPs in the HeLa tumor model, (b) the 64Cu–NOTA–FA–FI–PEG–PEI–Ac–Mn3O4 NPs in the FR-blocked HeLa tumor model, and (c) the 64Cu–NOTA–FI–PEG–PEI–Ac–Mn3O4 NPs in HeLa tumor. (d) Quantitative microPET imaging analysis of tumor uptake of the 64Cu-labeled NPs at different time points postinjection.