Validation of novel calibration scheme with traceable point-like 22Na sources on six types of PET scanners

To improve the reliability and convenience of the calibration procedure of positron emission tomography (PET) scanners, we have been developing a novel calibration path based on traceable point-like sources. When using Na-22 sources, special care should be taken to avoid the effects of 1.275-MeV gamma rays accompanying beta (+) decays. The purpose of this study is to validate this new calibration scheme with traceable point-like Na-22 sources on various types of PET scanners. Traceable point-like Na-22 sources with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons were used. The tested PET scanners included a clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and a small-animal PET scanner. The region of interest (ROI) diameter dependence of ROI values was 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 gamma rays. The observed ROI radius dependence was well represented with the assumed fitting function (R (2) > 0.994). The calibration factors determined using the point-like sources were consistent with those by the standard cross-calibration method within an uncertainty of +/- 4 %, which was reasonable considering the uncertainty in the standard cross-calibration method. This novel calibration scheme based on the use of traceable Na-22 point-like sources was successfully validated for six types of commercial PET scanners.