NG2 cells are ubiquitously distributed throughout the gray and white matter in the brain. NG2 cells undergo cell division and can generate oligodendrocytes and astrocytes as well as neurons even in the adult brain. It is known that NG2 cells become rapidly activated with their morphological changes including hypertrophy of the cell body and processes, and proliferate in response to several brain insults including traumatic injury, excitotoxic lesions and viral infections. Thus, establishment of in vivo imaging technique of NG2 cells could help us evaluate the extent of brain injury and repair processes. In this study, we generated a transgenic rat strain which preferentially overexpressed human estrogen receptorα ligand binding domain (hERL) in the NG2 cells (NG2-hERL Tg rat), and performed PET imaging of the cells in the brain using 16α-[¹⁸F]fluoro-17β-estradiol (FES), a PET tracer for hERL.