Comparison of Normalization Methods for ${^{124}}{\rm I}$ PET on Siemens Inveon PET Scanner

⁶⁸Ge has conventionally been used for the normalization of ¹⁸F PET. However, because ¹²⁴I PET has different characteristics such as a low positron branching ratio (23%), the presence of higher gamma energy (602 keV and 723 keV), and a larger positron range, the use of ⁶⁸Ge should be validated for ¹²⁴I PET. To the best of our knowledge, there has been no previous report on the effect of normalization between conventional ⁶⁸Ge and ¹²⁴I. In this study, we examined image quality to assess the effect of normalization. For this purpose, we measured the non-uniformities (NUs) and recovery coefficients (RCs) using a NEMA NU4 image quality phantom (NU4 phantom) and compared the values for the conventionally used ⁶⁸Ge and ¹²⁴I. A Siemens Inveon PET scanner was used throughout. Emission data were obtained using the NU4 phantom filled with ¹²⁴I solution (3.7 MBq) for 20 min within 250-750 keV. The normalization data were acquired for 40 h using a cylindrical phantom (diameter: 6 cm, length: 13.5 cm) filled with ¹²⁴I in a water solution (9.25 MBq). To match the energy window of an emission scan, the energy window setting for the normalization was 250-750 keV. The obtained list mode data were sorted into 3D sinograms. For comparison, normalization data were acquired using a cylindrical ⁶⁸Ge normalization phantom (diameter: 6 cm, length: 15 cm). The data with no normalization correction were also acquired. The list mode emission PET data were reconstructed using FBP with a ramp filter and normalization, and attenuation and scatter correction were applied. The image quality of the reconstructed images was assessed in terms of the radial, axial, and volume NUs and RCs as a standard using the NEMA NU4 protocol. There were no significant differences in the NUs and RCs between ⁶⁸Ge and ¹²⁴I. These results indicate that conventional <- up>68Ge can be used for ¹²⁴I PET.