The development of the Kety-Schmidt technique for the measurement of cerebral blood flow and metabolism (Kety and Schmidt, 1948) led to a significantly increased interest in the cerebral circulation. The ability to make quantitative measurements, especially in humans, provided investigators with the tools for collecting data not obtainable by previous means. As a tremendous amount of data began to be collected, it soon became obvious that the brain, unlike many other organs, is extremely heterogeneous in nature. Physiologic stimuli that, intuitively, would be expected to produce an alteration in cerebral blood flow and/or metabolism (and have subsequently been shown to produce regional changes) do not appear to cause any measureable changes in global cerebral blood flow or metabolism. This includes sleep (Mangold et al., 1955) and intellectual effort (Sokoloff et al., 1955). It is this heterogeneous nature of brain function that has prompted the development of techniques yielding regional or local information on cerebral hemodynamics and metabolism. Principal among these are autoradiographic methods for visualizing local function. Autoradiography, the production of an image from the radioactive decay occurring in a specimen, is only a tool for determining tissue radionuclide levels, and as such is not specific to the measurement of any particular parameter.