European Journal of Nuclear Medicine and Molecular Imaging | 2021
Dynamic PET imaging with ultra-low-activity of 18F-FDG: unleashing the potential of total-body PET
Abstract
Total-body positron emission tomography (PET) has been a true revolution of modern biomedical instrumentation following its initiation about 5 years ago, when Simon Cherry and Ramsey Badawi from the University of California, Davis received a $15.5 million, 5-year NIH Grant to lead the consortium in September 2015 [1, 2]. By May 2018, the fabrication of the first total-body PET scanner was completed by the consortium with aid from several industrial collaborators. The scanner has a 194 cm axial field-of-view for PET imaging provided by > 500,000 detector elements, as well as an 80row, 160-slice CT scanner for anatomical imaging and PET attenuation correction [3, 4], and was later called the uEXPLORER PET/CT scanner (United Imaging Healthcare Co., Ltd.). This scanner has a coincidence time window of 4.5–6.9 ns (ring difference dependent), an energy resolution of 11.7%@511 keV, and a time resolution of 430 ps. In terms of sensitivity based on the NEMA NU-2 phantom, it was ~ 190 kcps/MBq (70 cm length) and ~ 150 kcps/MBq (200 cm length) respectively [5]. In November 2018, the first human images from the uEXPLORER scanner were presented at a Total-body PET workshop, which were acquired at the Department of Nuclear Medicine, Zhongshan Hospital, Fudan University (Shanghai, China). A 61-year-old male healthy volunteer was injected with 7.8 mCi of F-FDG, with just 1 min of data acquisition providing good quality PET images [4]. At the beginning of the EXPLORER consortium, it was claimed that with the total-body PET scanner, one could: image better (e.g., reconstruct at higher resolution and detect smaller lesions), image faster (e.g., perform total-body PET in 15–30 s and reduce respiratory motion), image longer (e.g., image for 5 more half-lives due to the 40-fold increase in dynamic range), and image gently (e.g., use 40-fold reduction of radioactivity dose which will enable PET scans in the young population, as well as more repeated scans in the adult population) [1]. These claims were successfully demonstrated through a series of well-designed studies and publications over the last 2 years [4, 6–11]. Indeed, this state-of-the-art scanner possesses many advantages over previously developed PET/CT scanners. In this issue of European Journal of Nuclear Medicine and Molecular Imaging, Dr. Shi, Dr. Gu, and colleagues reported that total-body dynamic PET imaging with ultra-low-activity (0.37 MBq/kg) conferred equal performance to full-activity (3.7 MBq/kg) PET imaging when investigating the kinetic metrics of F-FDG in 20 human subjects [12]. When analyzing the feasibility of ultra-low-activity totalbody PET dynamic imaging for mathematical quantification of the kinetic parameters of F-FDG, 5 s per frame were used for the initial 3 min after F-FDG injection, and 3 min per frame were used for the remainder of the scan. In this welldesigned and well-executed study, findings revealed that (1) No significant difference in rate constants (k1, k2, k3) in any organ was found between the full-activity and ultra-lowactivity groups. (2) All of the fitted models showed excellent goodness-of-fit in full-activity and ultra-low-activity groups, with the full-activity group models exhibiting smaller Akaike Information Criterion (AIC) and Schwarz Criterion (SC), which was expected. The only statistically significant differences were found in the brain. (3) Clear PET images of comparable quality were acquired for the ultra-low-activity group from 12 min onward after F-FDG injection. (4) PET data from the full-activity group generated significantly larger This article is part of the Topical Collection on Technology