With the rapid development of biomedical imaging techniques in clinic,significant advances have been made in early diagnosis of cancers.Magnetic resonance imaging(MRI)has its advantages such as no radiation,deep penetration,high spatial resolution and soft-tissue sensitivity compared with other imaging mehtods for example,computed tomography(CT),poistron emission tomography(PET)and optical imaging etc.[1].Particularly,the use of MRI contrast agents further provides the more precise data,and will greatly help the early diagnosis,visualization therapy,and prognosis evaluation in cancer [2].Recently,paramagnetic and superparamagnetic inorganic nanoparticles were widely investigated as MRI contrast agents [3].Moreover,these nanoparticles can be functionalized as visualized nanoprobes for multimodal imaging(MRI,CT,fluorescence,upconversion luminescence(UCL),and PET etc.)and multifunctional therapy(photodynamic therapy(PDT),photothermal therapy(PTT),chemotherapy,and radiotherapy).Therefore,it is very necessary to develop MRI contrast agents based on inorganic nanoparticles for visualized theranostics in cancers.