Physical and Physiological Principles of Perfusion and Permeability

Perfusion describes the microcirculation and passage of fluid through specific tissue and organs. The capillaries serve this purpose, constituting a highly responsive system of homeostasis, which ensures that functional needs are met, through tight regulation of the microcirculation. This intricate system functions through the interplay between several highly specialized cell types. In the brain, the endothelial cells of the vessel wall are further specialized, and together with the glial cells they constitute the blood-brain barrier, restricting the passage of harmful substances into the neuropil. Magnetic Resonance Imaging has recently made significant advances in accurately measuring physiological variables related to this system, such as perfusion, blood volume, and permeability of the capillary wall as well as capillary transit time heterogeneity, allowing for specific in vivo characterization of both healthy and diseased human tissues.