Comparison of Static and Dynamic 18F-FDG PET/CT for Quantification of Pulmonary Inflammation in Acute Lung Injury.

PET imaging with 18F-FDG followed by mathematic modeling of the pulmonary uptake rate (Ki) is the gold standard for assessment of pulmonary inflammation in experimental studies of acute respiratory distress syndrome (ARDS). However, dynamic PET requires long imaging and allows the assessment of only 1 cranio-caudal field of view (∼15 cm). We investigated whether static 18F-FDG PET/CT and analysis of SUV or standardized uptake ratios (SURstat, uptake time-corrected ratio of 18F-FDG concentration in lung tissue and blood plasma) might be an alternative to dynamic 18F-FDG PET/CT and Patlak analysis for quantification of pulmonary inflammation in experimental ARDS. Methods: ARDS was induced by saline lung lavage followed by injurious mechanical ventilation in 14 anesthetized pigs (29.5-40.0 kg). PET/CT imaging sequences were acquired before and after 24 h of mechanical ventilation. Ki and the apparent volume of distribution were calculated from dynamic 18F-FDG PET/CT scans using the Patlak analysis. Static 18F-FDG PET/CT scans were obtained immediately after dynamic PET/CT and used for calculations of SUV and SURstat Mean Ki values of the whole imaged field of view and of 5 ventro-dorsal lung regions were compared with corresponding SUV and SURstat values, respectively, by means of linear regression and concordance analysis. The variability of the 18F-FDG concentration in blood plasma (arterial input function) was analyzed. Results: Both for the whole imaged field of view and ventro-dorsal subregions, Ki was linearly correlated with SURstat (r2 ≥ 0.84), whereas Ki-SUV correlations were worse (r2 ≤ 0.75). The arterial input function exhibited an essentially invariant shape across all animals and time points and can be described by an inverse power law. Compared with Ki, SURstat and SUV tracked the same direction of change in regional lung inflammation in 98.6% and 84.3% of measurements, respectively. Conclusion: The Ki-SURstat correlations were considerably stronger than the Ki-SUV correlations. The good Ki-SURstat correlations suggest that static 18F-FDG PET/CT and SURstat analysis provides an alternative to dynamic 18F-FDG PET/CT and Patlak analysis, allowing the assessment of inflammation of whole lungs, repeated measurements within the period of 18F-FDG decay, and faster data acquisition.