Performance evaluation of the uEXPLORER Total-body PET/CT scanner based on NEMA NU 2-2018 with additional tests to characterize long axial field-of-view PET scanners.

The world's first total-body PET scanner with an axial field-of-view (AFOV) of 194 cm is now in clinical and research use at our institution. The uEXPLORER PET/CT scanner, developed through a collaboration between the University of California, Davis (UC Davis) and United Imaging Healthcare (UIH), is the first commercially available total-body PET scanner. Here we present a detailed physical characterization of the uEXPLORER PET scanner based on NEMA NU-2-2018 along with a new set of measurements devised to appropriately characterize the total-body scanner. Methods: Sensitivity, count-rate performance, time-of-flight resolution, spatial resolution, and image quality were evaluated following the NEMA NU-2-2018 protocol. Additional measurements of sensitivity and count-rate capabilities more representative of total-body imaging were performed using extended geometry phantoms based on the world average human height (~165 cm). Lastly, image quality throughout the long AFOV was assessed with the NEMA image quality (IQ) phantom imaged at five axial positions and over a range of expected total-body PET imaging conditions (low dose, delayed imaging, short scan duration). Results: Our performance evaluation of the uEXPLORER PET system demonstrates that the scanner provides a very high sensitivity of 174 kcps/MBq, count-rate performance with a peak noise equivalent count-rate (NECR) of approximately 2 Mcps for total-body imaging, coupled with good spatial resolution capabilities for human imaging (≤ 3.0 mm FWHM near the center of the AFOV). Excellent image quality, contrast recovery, and low noise properties were illustrated across the AFOV in both NEMA IQ phantom evaluations and human imaging examples. Conclusion: In addition to standard NEMA NU-2-2018 characterization, a new set of measurements based on extending NEMA NU-2-2018 phantoms and experiments were devised to characterize the physical performance of the first total-body PET system. Rationale for these extended measurements was evident from differences in sensitivity, count-rate - activity relationships, and NECR limits imposed by differences in deadtime and randoms fraction between the NEMA NU-2 70 cm phantoms and the more representative total-body imaging phantoms. Overall, the total-body uEXPLORER PET system provides ultra-high sensitivity that supports excellent spatial resolution and image quality throughout the FOV in both phantom and human imaging.