Fig. 1.

The 2-tissue compartmental model of 2-[¹⁸F]fluoro-2-deoxygalactose (FDGal) metabolism fitted to data (4k model). q₁, Pool of FDGal in sinusoidal blood compartment; q₂, intracellular pool of FDGal; q₃, intracellular pool of FDGal metabolites, primarily FDGal-1-phosphate. K₂₁, unidirectional clearance of blood FDGal into hepatocytes (ml blood·min⁻¹·ml liver tissue⁻¹); k₁₂, rate constant for backflux of FDGal from hepatocytes back to the systemic circulation (min⁻¹); k₃₂, rate constant of enzymatic conversion of FDGal to FDGal-1-phosphate by galactokinase (min⁻¹); k₂₃, rate constant for dephosphorylation of FDGal-1-P (min⁻¹). On the basis of initial fittings, K₂₁ was set equal to the hepatic blood perfusion, Q (see text for details). The parameter k₂₃ was ignored in the calculation of the net metabolic clearance of FDGal by galactokinase from linear representation of the data (3k model).