Stem cells therapy appears to be ideally suited for tissue repair and many other diseases,and has achieved gratifying results in various tissue,ischaemic,degenerative,and other diseases.It is greatly important to understand their in vivo migration dynamics and differentiation processes.Magnetic resonance imaging is a well-suited tool to noninvasively monitor the cell distribution with high sensitivity and resolution.Nowadays,magnetic nanoparticles(MNPs)are gaining increasing interest in cell tracking as contrast agents.MNPs with different morphologies usually have different saturation magnetization and relaxivity.These properties determine the penetration stability and labelling efficiency of stem cells.However,water stability and surface properties limit their bio-applications and cellular affinity.Therefore,surface modifications would largely enhance the stability and biocompatibility to conquer physiological barriers.These modified strategies may vastly improve cell detection,tracking,and monitoring therapeutic outcomes.