Application of novel calibration scheme based on traceable point-like 22Na sources to various types of PET scanners

Purpose: We have been developing a practical and reliable calibration scheme based on the use of traceable pointlike sources. In using ²²Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β⁺ decays. The purpose of this study is to validate this calibration method with traceable point-like ²²Na sources on various types of PET scanners. Method: The traceable point-like ²²Na sources with a spherical absorber design used in this study were of the same type as those used in a previous study. The tested PET scanners included one clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and one small-animal PET scanner. The ROI (region of interest) diameter dependence of ROI values were represented with a fitting function, which was assumed to consist of a recovery part due to spatial resolution and a quadratic background part originating from the scattered γ rays. Results: The calibration factors determined using the point-like source were consistent with those by the standard cross-calibration method within ±4%, which was comparable to the uncertainty of the standard cross-calibration method. Conclusion: The novel calibration scheme based on the use of traceable ²²Na point-like sources was validated for six types of commercial PET scanners.