Shortened Acquisition Protocols for the Quantitative Assessment of the 2-Tissue-Compartment Model Using Dynamic PET/CT ¹⁸F-FDG Studies

(A) Fitting of kinetic model for hepatocellular carcinoma of liver. Input curve was retrieved from abdominal aorta. Target curve is increasing over time because of high metabolism in lesion. Data from 0 to 30 min are obtained from dynamic PET/CT series, and 60-min value is retrieved from whole-body examination. χ² is 0.389, demonstrating high accuracy of curve fit based on modified SVM method. These results meet biologic requirements of compartment model (k_x ≤ 1) and are obtained without any setting of initial values for model parameters; therefore they are user-independent. (B) A 2-tissue-compartment model fit of data shown in A using Levenberg–Marquardt algorithm. Results demonstrate overfitting of k₂ with k₂ = 1.487. This result is not usable despite good curve fit, because it does not match model assumptions (e.g., k₂ ≤ 1). This algorithm is dependent on selection of initial compartment parameters for model. Therefore, it is dependent on experience of user, which may introduce bias.