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Given the constant pressure to increase patient throughput while respecting radiation protection, global body PET image quality (IQ) is not satisfactory in all patients. We first studied the association between IQ and other variables, in particular body habitus, on a digital PET/CT. Second, to improve and homogenize IQ, we evaluated a deep learning PET denoising solution (Subtle PET TM ) using convolutional neural networks. We analysed retrospectively in 113 patients visual IQ (by a 5-point Likert score in two readers) and semi-quantitative IQ (by the coefficient of variation in the liver, CV liv ) as well as lesion detection and quantification in native and denoised PET. In native PET, visual and semi-quantitative IQ were lower in patients with larger body habitus ( p < 0.0001 for both) and in men vs. women ( p ≤ 0.03 for CV liv ). After PET denoising, visual IQ scores increased and became more homogeneous between patients (4.8 ± 0.3 in denoised vs. 3.6 ± 0.6 in native PET; p < 0.0001). CV liv were lower in denoised PET than in native PET, 6.9 ± 0.9% vs. 12.2 ± 1.6%; p < 0.0001. The slope calculated by linear regression of CV liv according to weight was significantly lower in denoised than in native PET ( p = 0.0002), demonstrating more uniform CV liv . Lesion concordance rate between both PET series was 369/371 (99.5%), with two lesions exclusively detected in native PET. SUV max and SUV peak of up to the five most intense native PET lesions per patient were lower in denoised PET ( p < 0.001), with an average relative bias of -7.7% and -2.8%, respectively. DL-based PET denoising by Subtle PET TM allowed [ 18 F]FDG PET global image quality to be improved and homogenized, while maintaining satisfactory lesion detection and quantification. DL-based denoising may render body habitus adaptive PET protocols unnecessary, and pave the way for the improvement and homogenization of PET modalities.

Aim: To perform a comprehensive analysis of discordances between contrast-enhanced CT (ceCT) and 18 F-FDG PET/CT in the evaluation of the extra-cerebral treatment monitoring in patients with stage IV melanoma., Materials and Methods: We conducted a retrospective monocentric observational study over a 3-year period in patients referred for 18 F-FDG PET/CT and ceCT in the framework of therapy monitoring of immune checkpoint (ICIs) as of January 2017. Imaging reports were analyzed by two physicians in consensus. The anatomical site responsible for discordances, as well as induced changes in treatment were noted., Results: Eighty patients were included and 195 pairs of scans analyzed. Overall, discordances occurred in 65 cases (33%). Eighty percent of the discordances (52/65) were due to 18 F-FDG PET/CT scans upstaging the patient. Amongst these discordances, 17/52 (33%) led to change in patient's management, the most frequent being radiotherapy of a progressing site. ceCT represented 13/65 (20%) of discordances and induced changes in patients' management in 2/13 cases (15%). The most frequent anatomical site involved was subcutaneous for 18 F-FDG PET/CT findings and lung or liver for ceCT., Conclusions: Treatment monitoring with 18 F-FDG PET/CT is more efficient than ceCT and has a greater impact in patient's management.