Disease activity and ¹⁸F-FDG uptake in organising pneumonia: semi-quantitative evaluation using computed tomography and positron emission tomography

Purpose: The present study was conducted to evaluate whether ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) in combination with computed tomography (CT) reflects disease activity in patients with organising pneumonia.Methods: Eighty-eight subjects who were normal (n=66) or who had proven organising pneumonia (n=22) underwent FDG-PET and CT imaging. The subjects included 55 men and 33 women, ranging in age from 24 to 63 years (mean 47 years). PET and CT data sets were digitally fused using a conformational PET/CT fusion algorithm. All scans were evaluated independently by two chest radiologists who were unaware of other clinical data. The visual score, maximal and mean standardised uptake value (SUV), and maximal and mean lesion-to-normal tissue ratio (LNR) were calculated. The imaging results were compared with the laboratory and pulmonary function test results. The inflammatory cells in the lesions were quantified immunohistochemically.Results: The visual score, maximal and mean SUV, and maximal and mean LNR of the patients with organising pneumonia were significantly higher than those of the normal subjects. The patients with air-space consolidation had a significantly higher SUV than those without air-space consolidation (mean±SD 3.08±0.39 vs 2.35±0.56; p<0.05). The number of CD45⁺ cells was positively correlated with the maximal SUV (r=0.632, p<0.01) and the maximal LNR (r=0.453, p<0.05). The number of CD8⁺ T lymphocytes also showed positive correlations with the maximal SUV (r=0.540, p<0.01) and the maximal LNR (r=0.547, p<0.01).Conclusion: Patients with organising pneumonia have an enhanced FDG accumulation which reflects the degree of disease activity.