Determine a proper protocol for routine 18F-FDG uEXPLORER Total-Body PET/CT scan

Abstract Background The axial length of a conventional PET/CT scanner is about 15–30 cm. However, uEXPLORER Total-Body PET/CT has an ultra-long axial field of view of 194 cm. By taking full use of all the scintillation photons, uEXPLORER has a 40 times higher sensitivity for photon detection relative to the conventional PET/CT. Ordered subset expectation maximization (OSEM) is a commonly used iterative algorithm in PET, however, it has a limitation that the image noise will increase when large number iteration is selected. A new penalized-likelihood iterative PET reconstruction, termed HYPER Iterative, was invented and now is available on the uEXPLORER Total-Body PET/CT. To date, its impact in lesion conspicuity in the patients with full injected dose or half injected dose was unclear. The goal of this study is to determine a proper protocol for routine 18F-FDG uEXPLORER Total-Body PET/CT scan. Results The quality of the 5 min PET image was excellent (score 5) for all the dose and reconstructed methods. Using the HYPER iterative method, PET image reached the excellent quality at 1 min with full-dose, and at 2 min with half-dose. While PET image reached a similar excellent quality at 2 min with full-dose and 3 min with half-dose using OSEM. The noise in OSEM reconstruction was higher than that by HYPER Iterative. Compared to OSEM, HYPER Iterative had slightly higher SUVmax and TBR of the lesions for large positive lesions (≥ 2cm) (SUVmax: up to 9% higher in full-dose and up to 13% higher in half-dose; TBR: up to 9% higher in full-dose and up to 23% higher in half-dose). For small positive lesions(≤ 10mm), HYPER Iterative had obviously higher SUVmax and TBR of the lesions (SUVmax: up to 45% higher in full-dose and up to 75% higher in half-dose; TBR: up to 45% higher in full-dose and up to 94% higher in half-dose). Conclusions Our study demonstrates that 1min scan with full dose and 2 min with half dose is proper for clinical diagnosis using HYPER Iterative, and 2 to 3 min scan for OSEM reconstruction. For detection of the small lesions, HYPER Iterative reconstruction is preferred.