Figure 1.

Visual representation of the different kinetic models. (a) Schematic of a two-tissue-compartment model with one input function (2C1i). Transfer coefficients K₁ and k₂ describe the uptake and washout of the free tracer and its metabolite ([¹⁸F]FBet) across cell membranes. Rate constant k₃ is regarded as the conversion of [¹⁸F]FCho into [¹⁸F]FPCho, which is assumed to be metabolically trapped in the cell. Micro-parameter k₄ represents dephosphorylation and is expected to be very small. (b) Schematic of a three-tissue-compartment model with two input functions (3C2i). Rate constants K_1p and K_1m, or k_2p and k_2m represent respectively the uptake and washout of [¹⁸F]FCho and [¹⁸F]FBet.