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 (K_i) 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 (SUR_stat, 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. K_i 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 SUR_stat Mean K_i values of the whole imaged field of view and of 5 ventro-dorsal lung regions were compared with corresponding SUV and SUR_stat 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, K_i was linearly correlated with SUR_stat (r² ≥ 0.84), whereas K_i-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 K_i, SUR_stat and SUV tracked the same direction of change in regional lung inflammation in 98.6% and 84.3% of measurements, respectively. Conclusion: The K_i-SUR_stat correlations were considerably stronger than the K_i-SUV correlations. The good K_i-SUR_stat correlations suggest that static ¹⁸F-FDG PET/CT and SUR_stat 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.