Background Highly sensitive digital total-body PET/CT scanners (uEXPLORER) have great potential for clinical applications and fundamental research. Given their increasing sensitivity, low-dose scanning or snapshot imaging is now possible in clinics. However, a standardized total-body 18F-FDG PET/CT protocol is still lacking. Establishing a standard clinical protocol for total-body 18F-FDG PET/CT examination under different activity administration plans can help provide a theoretical reference for nuclear radiologists. Methods The NEMA image quality (IQ) phantom was used to evaluate the biases of various total-body 18F-FDG PET/CT protocols related to the administered activity, scan duration, and iterations. Several objective metrics, including contrast recovery (CR), background variability (BV), and contrast-to-noise ratio (CNR), were measured from different protocols. In line with the European Association of Nuclear Medicine Research Ltd. (EARL) guidelines, optimized protocols were suggested and evaluated for total-body 18F-FDG PET/CT imaging for three different injected activities. Results Our NEMA IQ phantom evaluation resulted in total-body PET/CT images with excellent contrast and low noise, suggesting great potential for reducing administered activity or shortening the scan duration. Different to the iteration number, prolonging the scan duration was the first choice for achieving higher image quality regardless of the activity administered. In light of image quality, tolerance of oncological patients, and the risk of ionizing radiation damage, the 3-min acquisition and 2-iteration (CNR = 7.54), 10-min acquisition and 3-iteration (CNR = 7.01), and 10-min acquisition and 2-iteration (CNR = 5.49) protocols were recommended for full-dose (3.70 MBq/kg), half-dose (1.95 MBq/kg), and quarter-dose (0.98 MBq/kg) activity injection schemes, respectively. Those protocols were applied in clinical practices, and no significant differences were observed for the SUVmax of large/small lesions or the SUVmean of different healthy organs/tissues. Conclusion These findings support that digital total-body PET/CT scanners can generate PET images with a high CNR and low-noise background, even with a short acquisition time and low administered activity. The proposed protocols for different administered activities were determined to be valid for clinical examination and can maximize the value of this imaging type.
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.
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