The effect of respiratory gating on [18F]FDG PET/CT quantification in systemic sclerosis-associated interstitial lung disease

Respiratory motion influences quantification of [ 18 F]FDG PET/CT in the lungs. As a corrective measure, respiratory gating has shown benefits in patients with lung cancer but has not been investigated in patients with systemic sclerosis-associated interstitial lung disease (SSc-ILD), who have a diffuse increase in lung density. Therefore, we aimed to investigate the effects of phase-based respiratory gating on different measures for PET/CT quantification (MLV=Metabolic Lung Volume, TLG=Total Lesion Glycolysis, SUV mean , SUV max , and SUV tq =mean, maximum, and top quartile Standardized Uptake Value), using reconstructions with 5%–100% of the phase around end-inspiration (gate-5% to gate-100%). Fourteen patients with SSc-ILD and three SSc patients without ILD were included. Based on quantitative results, the gate with 25% of the phase surrounding end-inspiration (gate-25%) was chosen as the optimal gate requiring minimal data. In SSc-ILD patients, MLV and TLG showed a non-significant decrease of -7.81 and -6.89% (gate-25% vs gate-100%; P = 0.18 and P = 0.33, respectively). In the dorsobasal lung fields, which showed highest [ 18 F]FDG uptake, gating (gate-25% vs gate-100%) led to a minor decrease in SUV mean (median -4.00% to -0.72%; P = 0.001 and P = 0.83) and non-consistent, non-significant effects on SUV max (median -1.82 to +7.12%; P = 0.25 and P = 0.26). SUV tq showed an intermediate pattern compared to SUV mean , and SUV max . In areas with lowest [ 18 F]FDG uptake (apical and ventral lung fields), we found similar effects of phase-based gating for all quantitative measures. No evident effects of phase-based gating were observed in SSc patients without ILD. Phase-based respiratory gating had limited effect on [ 18 F]FDG PET/CT quantification in patients with SSc-ILD. These results are likely explained by the diffuse nature of ILD and the fact that most of our patients had limited ILD extent. Based on these outcomes, the routine application of respiratory gating in this specific group of patients is currently not advocated.