Basic principles for imaging blood flow

The investigation of blood flow represents one of the most fundamental problems faced in physiology. Any abnormalities in macro- or microvasculature may affect a given organ's functionality. Perturbations or alterations of blood flow are evident in many disease conditions, including neurodegenerative disorders, vascular and organ disease, and cancer. This highlights the importance of blood flow assessment and perfusion through both qualitative visual inspection and accurate quantification. Perfusion is defined broadly as the passage of fluid through channels in a structure. For the human body, and in this book, perfusion is the microvascular blood flow through capillary beds in organs or tissue, delivering oxygen and nutrients and draining waste products, rather than, for example, lymphatic perfusion.