Assessment of Regional Lung Ventilation with Positron Emission Tomography Using the Radiofluorinated Gas [18F]SF6: Application to an Animal Model of Impaired Ventilation.

ABSTRACT

PURPOSE: Clinical ventilation studies are primarily performed with computerized tomography (CT) and more often with single-photon emission Computerized tomography (SPECT) using radiolabelled aerosols, both presenting certain limitations. Here, we investigate the use of the radiofluorinated gas [18F]SF6 as a positron emission tomography (PET) ventilation marker in an animal model of impaired lung ventilation. PROCEDURES Sprague-Dawley rats (n = 15) were randomly assigned to spontaneous ventilation (sham group), endotracheal administration of phosphate-buffered saline (PBS group), or endotracheal administration of lipopolysaccharide (LPS group). PET-[18F]SF6 images (10-min acquisition) were acquired at t = 48 h after LPS or PBS administration under mechanical ventilation. CT images were acquired after each PET session. Volumes of interest were manually delineated in the lungs on CT images, and voxel-by-voxel analysis was carried out on PET images to obtain the corresponding histograms. After the imaging sessions, lungs were harvested to conduct histological analysis. RESULTS: Ventilation studies in sham animals showed uniform distribution of [18F]SF6 and fast elimination of the radioactivity after discontinuation of the administration. For PBS- and LPS-treated rats, ventilation defects were observed on PET images in some animals, identified as regions with low presence of the radiolabelled gas. Hypoventilated areas co-localized with regions with higher x-ray attenuation than healthy lungs on the CT images, suggesting the presence of oedema and, in some cases, atelectasis. Histograms obtained from PET images showed quasi-Gaussian distributions for control animals, while PBS- and LPS-treated animals demonstrated the presence of hypoventilated voxels. Deviation of the histograms from Gaussian distribution correlated with histological score was obtained by ex vivo histological analysis. CONCLUSIONS: [18F]SF6 is an appropriate marker of regional lung ventilation and may find application in the early diagnose of acute lung disease.