Image-Derived Input Function for Assessment of 18F-FDG Uptake by the Inflamed Lung

Pulmonary uptake of 18F-FDG assessed with PET has been used to quantify themetabolic activity of inflammatory cells in the lung. This assessment involves modeling of tracer kinetics and knowl-edge of a time–activity curve in pulmonary artery plasma as an input function, usually acquired by manual blood sampling. This paper presents and validates a method to accurately derive an input function from a blood-pool region of interest (ROI) de-fined in dynamic PET images. Methods: The method is based on a 2-parameter model describing the activity of blood and that from spillover into the time–activity curve for the ROI. The model parameters are determined using an iterative algorithm, with 2 blood samples used to calibrate the raw PET-derived ac-tivity data. We validated both the 2-parameter model and the method to derive a quantitative input function from ROIs defined for the cavities of the right and left heart and for the descendin