A Gd-doped ultrasmall CeO2 contrast agent was prepared with high longitudinal relaxivity (r1 = 10.1 mM-1 s-1, 7.0 T) through rationally regulating the crystallinity and surface coatings, providing a new paradigm for optimizing MRI performance. Moreover, responsive photoacoustic imaging (PAI) was established via tumor microenvironment-triggered oxidation, affording dual-modal imaging.
