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. Author manuscript; available in PMC: 2010 Mar 1.
Published in final edited form as: J Nucl Med. 2009 Feb 17;50(3):356–363. doi: 10.2967/jnumed.108.058776

Figure 1.

Figure 1

Three-compartment model for α[11C]methyl-L-tryptophan (AMT) kinetics in lung tumor, using first-order rate constants (17). The transport rate constant K1 and the outflow rate constant k2 describe the exchange of AMT between vascular space (CP) and the cell cytoplasm where it constitutes the free compartment (Cf). Irreversible enzymatic conversion of AMT to its metabolite(s) (in the metabolic pool Cm) is characterized by the metabolic rate constant k3. Efflux of AMT metabolites from the metabolic compartment can be represented by rate constant k4. Although, theoretically, AMT metabolites could move from the metabolic pool (Cm) to both the free compartment (Cf) and the vascular space (CP), the applied kinetic modeling included efflux of the tracer metabolites from the entire tissue compartment. The dotted arrow represents the fact that k4 was poorly identifiable in the full model and was eventually set to zero (see Results); thus, the final analysis included only three kinetic rate constants (K1, k2 and k3).