Figure 1.

Schematic representation of the two-compartmental pharmacokinetic (PK) Tofts model comprising an intra-vascular compartment (left) and extravascular -extracellular space (EES) compartment (right). The volume transfer between the two compartments is depicted by the transfer constant between the blood plasma and the EES (K^trans) and the transfer constant between the EES and blood plasma (k_ep), respectively. k_ep can be calculated using k_ep = K^trans /ν_e, whith ν_e volume of the EES per unit volume of tissue.