Blood capillary function in the context of tracer kinetics lies principally in capillary permeability-surface area product, which determines rate of transport of tracers across vascular endothelium into the interstitial space, and whether transport is perfusion-dependent or diffusion-dependent. Another important property of a capillary is its reflection coefficient, which is related to permeability. In nuclear medicine, capillary function is especially important in lymphoscintigraphy and myocardial perfusion scintigraphy.