This model has been developed by Bertoldo et al.  for the analysis of FDG uptake in skeletal muscle. In this context C1, C2 and C3 correspond to extracellular, intracellular and phosphorylated intracellular FDG. K1 [ml/ccm/min] and k2 [1/min] are the exchange rate constants between plasma and the extracellular space, k3 [1/min] and k4 [1/min] describe the transport in and out of the cell, k5 [1/min] and k6 [1/min] phosphorylation and dephosphorylation.
Differential Equation of the Mass Balance
with input curve Cp(t).
Operational Model Curve
with the concentration CB(t) of tracer in whole blood, and the blood volume fraction vB.
The model includes the 6 fitable parameters vB, K1, k2, k3, k4, k5, k6. Usually, vB is fixed at a physiologic value of 3-5%, and k6 is fixed: k6=0. The influx Ki is given by
1.Bertoldo A, Peltoniemi P, Oikonen V, Knuuti J, Nuutila P, Cobelli C: Kinetic modeling of [18F]FDG in skeletal muscle by PET: a four-compartment five-rate-constant model. American journal of physiology Endocrinology and metabolism 2001;281(3):E524-536. PDF