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FIGURE 1. Compartmental model for [11C]-(R)-PK11195 assumes a target region with a specific bound fraction and a compartment for a free fraction plus possibly a nonspecific bound fraction (NS) that equilibrates fast with the unbound fraction. The (ideal) reference region should be devoid of PBBSs and, therefore, be fitted best with a 1-tissue compartment model. K1 and k2 represent first-order rate constants for transport of ligand from plasma to tissue and vice versa (K1' and k2' for reference region); k3 and k4 represent rate constants between the free and specifically bound compartments in tissue.
