FDG 2-Tissue Compartment Model

The 2-tissue compartment model for FDG has the same structure as the standard model.

Differential Equation of the Mass Balance

with FDG concentration of in arterial plasma C_p(t), FDG concentration C₁(t) and phosphorylated FDG (FGD-6-P) concentration C₂(t) in tissue. K₁ [ml/ccm/min] and k₂ [1/min] are the uptake and clearance rate constants, whereas k₃ [1/min] represents phosphorylation by hexokinase and k₄ [1/min] dephosphorylation.

Operational Model Curve

with the concentration C_B(t) of tracer in whole blood, and the blood volume fraction v_B.

Parameter Fitting

The model includes the 5 fitable parameters vB, K1, k2, k3, k4. Usually, vB is fixed at a physiologic value of 3-5% to reduce the number of fitted parameters, and dephosphorylation is so slow that k₄ is fixed k4=0.

FDG-specific Results

The FDG model has two additional input parameters, the lumped constant (LC) and the plasma glucose concentration (PG [mmol/l]). In combination with the estimated K₁, k₂, and k₃ parameters they allow calculating the metabolic rate of glucose MRGlu

Note that the LC and PG values are maintained when switching back and forth with the Patlak model, if the Model conversion option in the Extras panel is enabled.