This book describes the methods for measuring cerebral blood flow (CBF) using radioactive tracers, positron emission tomography (PET) and single photon emission computed tomography (SPECT). Divided into nine chapters, the book covers the attributes, history, theory, and measurement methodology for CBF. It also explains the pathophysiology of brain vascular problems. The temporal and spatial fluctuations of CBF in correspondence with neuronal activity provide us with a new window onto how the brain works. The book details the theories and methodologies for measuring CBF and reviews advances in technology from the era of Kety-Schmidt to the present. The book is targeted at scientists, clinicians and medical students who wish to know more about the principles of tracer kinetics in quantitative measurement of CBF. It discusses the diagnosis of brain pathophysiology via CBF and explores the only partially understood mechanisms that regulate fluctuations in brain function. Written in an accessible manner, the book may also help general readers to understand the fundamental role of CBF in supporting the brain's activities. .