Prone position PET/CT is useful in reducing gravity-dependent opacity related [18F]fluorodeoxyglucose uptake

Abstract Purpose We investigated whether [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) taken in the prone position could reduce [18F]FDG uptake in dependent lungs. Methods Patients who underwent [18F]FDG PET/CT in both supine and prone positions from October 2018 to September 2021 were reviewed retrospectively. [18F]FDG uptake of dependent and nondependent lungs was analysed visually and semi-quantitatively. A linear regression analysis was also performed to examine the association between the mean standardised uptake value (SUVmean) and the Hounsfield unit (HU). Results Totally, 135 patients (median age, 66 years [interquartile range: 58–75 years]; 80 men) were included. Dependent lungs showed significantly higher SUVmean and HU than nondependent lungs on both supine position PET/CT (sPET/CT, 0.59 ± 0.14 vs. 0.36 ± 0.09, p < 0.001; −671 ± 66 vs. −802 ± 43, p < 0.001; respectively) and prone position PET/CT (pPET/CT, 0.45 ± 0.12 vs. 0.42 ± 0.08, p < 0.001; −731 ± 67 vs. −790 ± 40, p < 0.001; respectively). In the linear regression analysis, there was a strong association between the SUVmean and HU in sPET/CT (R = 0.86, p < 0.001) and a moderate association in pPET/CT (R = 0.65, p < 0.001). One hundred and fifteen patients (85.2%) had visually discernible [18F]FDG uptake in the posterior lung on sPET/CT, which disappeared on pPET/CT in all but one patient (0.7%, p < 0.001). Conclusion [18F]FDG uptake of the lung had moderate-to-strong associations with HU. Gravity-dependent opacity-related [18F]FDG uptake can be effectively reduced on prone position PET/CT.