Assessment of SUV consistency in PET/CT with annulus 68Ge DQA phantom

Introduction: The standardized uptake value (SUV) is a crucial parameter in nuclear medicine PET/CT imaging, providing a semi-quantitative measure of radiotracer uptake. It plays a critical role in differentiating malignant from benign lesions before treatment and monitoring treatment response. Ensuring consistent SUV measurements is therefore an important criterion for the PET/CT scanner performance in terms of accurate quantification for follow-up patients. While daily quality control tests for PET/CT do not explicitly report SUV values, this study aims to evaluate the consistency of SUV measurements on this system using the daily quality assurance (DQA) phantom. This approach not only helps to determine the consistent SUV quantification but also detects any SUV variations that might arise in the system after any major breakdowns or repairs.

Methods: The SUV consistency test of the Discovery IQ 5-ring PET/CT scanner, GE Healthcare was performed at our institution, utilizing an annulus ⁶⁸Ge DQA phantom for evaluation. The phantom employed in this study exhibited an assayed activity of 1.49 mCi on January 1, 2022, with a volume of 1260 ml. Acquisition of the ⁶⁸Ge DQA phantom was carried out following our standard clinical PET/CT protocol for a single field of view with 26 cm axial coverage. Data were acquired in 3D acquisition mode with a one-bed position and a duration of 5 minutes. Images were reconstructed by the BSREM (block sequential expectation maximization) algorithm reconstruction with Q Clear, where the point spread function was automatically selected as Sharp IR with 350 selected as the beta factor. A three-dimensional region of interest was drawn on the axial slice of the entire phantom of the reconstructed image to determine the SUV_mean value on the first day of acquisition, which served as the baseline SUV_mean for this study. The identical acquisition protocol was repeated for 30 consecutive days. The mean and standard deviation of SUV_mean were calculated. The accuracy of subsequent observations was calculated with reference to the first-day observation. The coefficient of variation is also calculated for precision.

Results: The mean and standard deviation of SUVs for the ⁶⁸Ge DQA annulus phantom were 0.94 ± 0.0092 g/ml. The accuracy and coefficient of variation of SUVs for the ⁶⁸Ge DQA annulus phantom were 100% and 0.98%. The graph depicting observed SUVs versus time (days) for the ⁶⁸Ge DQA phantom revealed a linear relationship.

Conclusions: The study demonstrates that the consistency of SUVs measured on the PET/CT system with phantom exhibits a linear response with time, indicating consistent SUV values over the study period. This finding suggests that the annulus ⁶⁸Ge DQA phantom can be utilized effectively to determine the consistency of SUV quantification for the PET/CT system.