PET with 18F-FDG may be useful for quantifying neutrophilic activation. We previously demonstrated that pulmonary neutrophil sequestration could be detected during acute lung injury (ALI), even without migration into the alveolar compartment. Using the influx constant Ki as the method to quantify lung 18F-FDG uptake, we also showed that Ki correlated positively with in vitro assays of 3H-deoxyglucose (3H-DG) uptake in cells harvested via bronchoalveolar lavage. In the present study, we have reanalyzed data from that study to determine if simpler nonkinetic methods of quantifying the pulmonary uptake of 18F-FDG could be as powerful as calculating Ki.
Methods: 18F-FDG uptake was quantified as Ki, calculated by 3-compartmental model analysis (used as the gold standard) and Patlak graphical analysis, with and without normalization for initial volume of tracer distribution; the standardized uptake value; and the tissue-to-plasma activity ratio (TPR).
Results: Values for Ki, determined either from a 3-compartmental model analysis of the time-activity data or by Patlak graphical analysis, were highly correlated (R2 = 0.97). The correlation was worse if these variables were normalized for the initial volume of tracer distribution. TPR was highly correlated with Ki determined by the compartmental model (R2 = 0.96) and with in vitro measurements of 3H-DG uptake (R2 = 0.63).
Conclusion: The TPR is a simple and equally effective alternative to dynamic imaging in determining net 18F-FDG uptake during ALI. Normalization of the kinetic data for differences in the initial volume of tracer distribution does not contribute significantly to signal interpretation during ALI.