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

This study aimed to investigate whether performing [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) in the prone position could reduce [¹⁸F]FDG uptake in dependent lungs.

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 performed to examine the association between the mean standardised uptake value (SUV_mean) and the Hounsfield unit (HU).

A total of 135 patients (median age, 66 years [interquartile range: 58-75 years]; 80 men) were included. Dependent lungs showed significantly higher SUV_mean and HU than nondependent lungs on 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). Linear regression analysis revealed a strong association between the SUV_mean and HU in sPET/CT (R = 0.86, p < 0.001) and 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).

[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.

Prone position PET/CT effectively reduces gravity-dependent opacity-related [¹⁸F]fluorodeoxyglucose uptake in the lung, potentially improving diagnostic accuracy in evaluating nodules in dependent lungs and offering a more accurate assessment of lung inflammation parameters in interstitial lung disease evaluations.

• The study evaluated whether performing [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) PET/CT could reduce [¹⁸F]FDG uptake in lungs. • In prone and supine position PET/CT, the [¹⁸F]FDG uptake and Hounsfield unit were moderately to strongly associated. • Prone position PET/CT can reduce gravity-dependent opacity-related [¹⁸F]FDG uptake by the posterior lung.