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Inducible nitric oxide synthase (iNOS) activity increases in acute and chronic inflammatory lung diseases. Imaging iNOS expression may be useful as an inflammation biomarker for monitoring lung disease activity. We developed a novel tracer for PET that binds to iNOS in vivo, ¹⁸F-NOS. In this study, we tested whether ¹⁸F-NOS could quantify iNOS expression from endotoxin-induced lung inflammation in healthy volunteers. Healthy volunteers were screened to exclude cardiopulmonary disease. Qualifying volunteers underwent a baseline, 1-h dynamic ¹⁸F-NOS PET/CT scan. Endotoxin (4 ng/kg) was then instilled bronchoscopically in the right middle lobe. ¹⁸F-NOS imaging was performed again approximately 16 h after endotoxin instillation. Radiolabeled metabolites were determined from blood samples. Cells recovered by bronchoalveolar lavage (BAL) after imaging were stained …