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Modeling of Tracer Transport Delays for Improved Quantification of Regional Pulmonary F-FDG Kinetics, Vascular Transit Times, and Perfusion

Wellman, TJ;Winkler, T;Vidal Melo, MF;

F-FDG-PET is increasingly used to assess pulmonary inflammatory cell activity. However, current models of pulmonary F-FDG kinetics do not account for delays in F-FDG transport between the plasma sampling site and the lungs. We developed a three-compartment model of F-FDG kinetics that includes a delay between the right heart and the local capillary blood pool, and used this model to estimate regional pulmonary perfusion. We acquired dynamic F-FDG scans in 12 mechanically ventilated sheep divided into control and lung injury groups (n = 6 each). The model was fit to tracer kinetics in three isogravitational regions-of-interest to estimate regional lung transport delays and regional perfusion. NN bolus infusion scans were acquired during a period of apnea to measure regional perfusion using an established reference method. The delayed input function model improved description of F-FDG kinetics (lower Akaike Information Criterion) in 98% of studied regions. Local transport delays ranged from 2.0 to 13.6 s, averaging 6.4 2.9 s, and were highest in non-dependent regions. Estimates of regional perfusion derived from model parameters were highly correlated with perfusion measurements based on NN-PET (R = 0.92, p < 0.001). By incorporating local vascular transports delays, this model of pulmonary F-FDG kinetics allows for simultaneous assessment of regional lung perfusion, transit times, and inflammation.