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Figure 5. Vascular end-points, which will inform on the efficacy of antiangiogenic and antivascular drugs and which are accessible by clinically-applicable imaging techniques, are shown. Analysis of the initial tissue uptake kinetics of an intravenously administered contrast agent/radiotracer allows calculation of blood flow rate or the vascular permeability–surface area product, depending on whether the tissue uptake of the marker is flow or permeability limited. This will depend on characteristics of both the contrast agent itself and the vascular wall. Full quantification requires an arterial input function. The tissue/blood partition coefficient is the relative concentration of the agent in tissue and blood at equilibrium. The apparent tissue/blood partition coefficient can be accurately determined given relatively long imaging times and is equal to the true tissue/blood partition coefficient in well-perfused tissues. In poorly perfused tissue, it is reduced and reflects the perfused fraction of the tissue (see text). Measurement of the fraction of the tissue occupied by functional blood vessels (blood volume) is made using agents which are essentially confined to the vasculature. Analysis of venous blood samples allows for full quantification.
