Historical Background and Current Applications in Nuclear Medicine Imaging

90 Y is traditionally considered as a pure β – emitter. However, the decay of this radionuclide has a minor branch to the 0 + first excited state of 90 Zr at 1.76 MeV, that is followed by a β + /β – emission. This internal pair production has been largely studied in the past because it is generated by a rare electric monopole transition (E0) between the states 0 + /0 + of 90 Zr. The positronic emission has been recently exploited for nuclear medicine applications, i.e. positron emission tomography (PET) acquisitions of 90 Y-labelled radiopharmaceuticals, widely used as therapeutic agents in internal radiation therapy. To date, this topic is gaining increasing interest in the radiation dosimetry community, as the possibility of detecting β + emissions from 90 Y by PET scanners may pave the way for an accurate patient-specific dosimetry. This could lead to an explosion in scientific production in this field. In the present paper the historical background behind the study of the internal pair production of the 0 + /0 + transition of 90 Zr is presented along with most up to date measured branch ratio values. An overview of most recent studies that exploit β + particles emitted from 90 Y for PET acquisitions is also provided.