Development and validation of NEMA NU-2 equivalent sensitivity and scatter phantoms for PET performance characteristic evaluation

Abstract Objective This study aimed to evaluate the physical performance of a Philips Gemini TOF PET/CT system using in-house developed sensitivity and scatter phantoms. The assessment was conducted in accordance with the NEMA NU2-2007 guidelines. Methods We developed in-house NEMA NU-2 Sensitivity (NU-2IndiSen) and Scatter (NU-2IndiSc) phantoms. These phantoms were evaluated through a series of tests: the alpha test, which included dimension comparison and radiation exposure comparison, and the beta test, which involved comparing NEMA NU-2 sensitivity and scatter fractions. In the dimension test, we compared the diameters of the NU-2IndiSen and NU-2IndiSc phantoms with those of the NU-2Sen and NU-2Sc phantoms. The radiation exposure tests involved comparing the surface radiation exposure from the NU-2IndiSen and NU-2IndiSc phantoms with that from the NU-2Sen and NU-2Sc phantoms. The beta tests assessed the sensitivity and scatter fraction of the Gemini TF 64 PET system using the NU-2IndiSen and NU-2IndiSc phantoms and compared these measurements with those obtained using the NU-2Sen and NU-2Sc phantoms. Results The dimension tests revealed no significant differences (p-value > 0.05) between the NU-2IndiSen and NU-2Sen phantoms, as well as between the NU-2IndiSc and NU-2Sc phantoms. Similarly, the radiation exposure tests showed no significant differences (p-value > 0.05) in surface radiation exposure between the NU-2IndiSen and NU-2Sen phantoms, and between the NU-2IndiSc and NU-2Sc phantoms. The average system sensitivity measured using the NU-2IndiSen and NU-2Sen NEMA phantoms were 6724 cps/MBq and 6748 cps/MBq, respectively, both exceeding the vendor's acceptance limit of > 6700 cps/MBq. Similarly, the scatter fraction, noise equivalent count rate (NECR), activity at which peak NECR is achieved, and maximum true count rate performance measured using the NU-2IndiSc and NU-2Sc phantoms were 25.9, 106.4 kcps, 18.5 kBq/ml, and 243.2 kcps, and 27.14, 106.03 kcps, 15.68 kBq/ml, and 263.2 kcps, respectively, all well within the vendor's prescribed limits. Conclusion The results of this study demonstrate that the in-house developed sensitivity and scatter phantoms accurately assess the performance of the Philips Gemini TOF PET/CT system. The obtained values for system sensitivity, scatter fraction, NECR, and true count rate are in excellent agreement with the vendor-specified limits, validating the use of these phantoms for routine quality assurance procedures.