Quantitative 18F-fluorodeoxyglucose positron emission tomography/computed tomography to assess pulmonary inflammation in COPD

Rationale COPD and smoking are characterised by pulmonary inflammation. F-18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) imaging may improve knowledge of pulmonary inflammation in COPD patients and aid early development of novel therapies as an imaging biomarker. Objectives To evaluate pulmonary inflammation, assessed by FDG uptake, in whole and regional lung in "usual" (smoking-related) COPD patients, alpha-1 antitrypsin deficiency (alpha(1)ATD) COPD patients, smokers without COPD and never-smokers using FDG PET/CT. Secondly, to explore cross-sectional associations between FDG PET/CT and systemic inflammatory markers in COPD patients and repeatability of the technique in COPD patients. Methods Data from two imaging studies were evaluated. Pulmonary FDG uptake (normalised K-i; nK(i)) was measured by Patlak graphical analysis in four subject groups: 84 COPD patients, 11 alpha(1)ATD-COPD patients, 12 smokers and 10 never-smokers. Within the COPD group, associations between nK(i) and systemic markers of inflammation were assessed. Repeatability was evaluated in 32 COPD patients comparing nK(i) values at baseline and at 4-month follow-up. Results COPD patients, alpha(1)ATD-COPD patients and smokers had increased whole lung FDG uptake (nK(i)) compared with never-smokers (0.0037 +/- 0.001, 0.0040 +/- 0.001, 0.0040 +/- 0.001 versus 0.0028 +/- 0.001 mL.cm(-3).min(-1), respectively, p<0.05 for all). Similar results were observed in upper and middle lung regions. In COPD participants, plasma fibrinogen was associated with whole lung nK(i) (beta=0.30, p=0.02) in multivariate analysis adjusted for current smoking, forced expiratory volume in 1 s % predicted, systemic neutrophils and C-reactive protein levels. Mean percentage difference in nK(i) between the baseline and follow-up was 3.2%, and the within subject coefficient of variability was 7.7%. Conclusions FDG PET/CT has potential as a noninvasive tool to enable whole lung and regional quantification of FDG uptake to assess smoking- and COPD-related pulmonary inflammation.