Comparison of Imaging Characteristics of124I PET for Determination of Optimal Energy Window on the Siemens Inveon PET

Abstract

Purpose.124I has a half-life of 4.2 days, which makes it suitable for imaging over several days over its uptake and washout phases. However, it has a low positron branching ratio (23%), because of prompt gamma coincidence due to high-energyγ-photons (602 to 1,691 keV), which are emitted in cascade with positrons.Methods.In this study, we investigated the optimal PET energy window for124I PET based on image characteristics of reconstructed PET. Image characteristics such as nonuniformities, recovery coefficients (RCs), and the spillover ratios (SORs) of124I were measured as described in NEMA NU 4-2008 standards.Results.The maximum and minimum prompt gamma coincidence fraction (PGF) were 33% and 2% in 350~800 and 400~590 keV, respectively. The difference between best and worst uniformity in the various energy windows was less than 1%. The lowest SORs of124I were obtained at 350~750 keV in nonradioactive water compartment.Conclusion.Optimal energy window should be determined based on image characteristics. Our developed correction method would be useful for the correction of high-energy prompt gamma photon in124I PET. In terms of the image quality of124I PET, our findings indicate that an energy window of 350~750 keV would be optimal.