Abstract: Lutetium (Lu) based scintillators such as LSO and LYSO, are widely used in PET detectors due to their high stopping power for 511 keV gamma rays, high light yield and short decay time. The abundance of Lu-176 is 2.6% in natural Lu, and the Lu-176 is a long-lived radioactive isotope with a beta decay and three major simultaneous gamma decays. This phenomenon introduces random events to PET systems that affects the system imaging performance. On the other hand, the advantages of intrinsic radiation of Lu-176 continue to be exploited and utilized. The Lu-176 intrinsic radiation in PET detectors are reviewed, including the characteristic, the adverse effects, and its useful applications.