Fig. 2.

Principle of direct cell labeling. Principle of direct cell labeling methods is a strategy for imaging stem cells in vivo by introducing or labeling direct labeling agents into the body without genetic manipulation. Principle of direct cell labeling methods are relatively simple imaging methods that label stem cells with an agent in vitro and then implant them in vivo. QDs: quantum dots, CM-Dil: chloromethyl-benzamide dialkyl carbocyanine-Dil, MRI: magnetic resonance imaging, SPIONs: superparamagnetic iron-oxide nanoparticles, MNPs: magnetic nanoparticles, Ferumoxytol NPs: Feru-moxytol nanoparticles, CIONs-22s: cubic iron oxide nanoparticle, MPI: magnetic particle imaging, Radioisotope labeled NPs: Radio-isotope labeled nanoparticles, ¹⁸F-FDG: 2-deoxy-2-[18F]fluoro-D-glucose, GLUT1: glucose transporter 1, GVs: gas vesicles, ELS: exosome-like silica nanoparticles, TPSi NP: cell-penetrating peptide (virus-1 transactivator of transcription) conjugated porous silicon nanoparticle.