One of necessary steps before stem cell transplantation can be pushed on into clinic is finding a non-invasive method to track stem cells implanted inside human body. For high sensitivity and possibility of imaging various molecules within the cells as targets

molecular imaging with SPECT or PET has the most powerful potential to monitor stem cells transplanted in vivo among all the other imaging techniques. The possibility of in vivo tracking of stem cells with various strategies of radionuclide imaging was discussed respectively according to their characteristics and recent development. Receptor imaging may be firstly utilized to solve the problem for its simplicity but poor in its stability and universality. Screening with SELEX techniques

aptamer oligonucleotides specifically targeted to stem cells will be found. Combining antisense imaging with SELEX

the problem of tracing stem cells in vivo would be eventually and thoroughly solved.