Quantitative imaging of 124I and 86Y with PET

The quantitative accuracy and image quality of positron emission tomography (PET) measurements with 124I and 86Y is affected by the prompt emission of gamma radiation and positrons in their decays, as well as the higher energy of the emitted positrons compared to those emitted by 18F. PET scanners cannot distinguish between true coincidences, involving two 511-keV annihilation photons, and coincidences involving one annihilation photon and a prompt gamma, if the energy of this prompt gamma is within the energy window of the scanner. The current review deals with a number of aspects of the challenge this poses for quantitative PET imaging. First, the effect of prompt gamma coincidences on quantitative accuracy of PET images is discussed and a number of suggested corrections are described. Then, the effect of prompt gamma coincidences and the increased singles count rates due to gamma radiation on the count rate performance of PET is addressed, as well as possible improvements based on modification of the scanner’s energy windows. Finally, the effect of positron energy on spatial resolution and recovery is assessed. The methods presented in this overview aim to overcome the challenges associated with the decay characteristics of 124I and 86Y. Careful application of the presented correction methods can allow for quantitatively accurate images with improved image contrast.