Evaluation and calibration of PET scanners with a specially designed point-like radioactive source

Background: In order to evaluate the uncertainty in the radioactivity measurements performed using PET scanners and to determine the calibration factors of these scanners, it is essential that the radioactive sources are equipped with absorber materials that ensure the annihilation of positrons. Therefore, the evaluation and calibration depend on scatter and attenuation corrections in conventional techniques based on phantoms. Although an extrapolation method that involves the use of multiple absorber sleeves for a line radioactive source is effective in eliminating the dependence, the long line shape limits its application range. Objective: The objective of this study is to propose a point-like radioactive source with multiple absorber capsules, which can be used to evaluate the uncertainty in the radioactivity measurements performed using a PET scanner and to determine a calibration factor in a way that is independent of scatter and attenuation corrections. Methods: The proposed radioactive source consists of a small spherical radioactive part and a set of successively sized aluminum absorber capsules. Extrapolation over the total absorber thickness made it possible to estimate the results that were approximately free from scatter and absorption caused by the absorber materials. As an example application, the proposed method was used to a research PET scanner. In addition, the basic characteristic of the point-like radioactive source was investigated using a Monte Carlo simulation code. Results and Conclusion: Performance characteristics and a calibration factor of the PET scanner were successfully evaluated and determined. Therefore, the proposed method is useful for this purpose. Further studies are expected to improve the design of the radioactive source and enhance the practicability and traceability of our proposed method.