What is “power”? Most people have an intuitive notion of what it means. But scientists have not yet formulated a statement of the concept of power that is rigorous enough to be of use in the systematic study of this important social phenomenon. Power is here defined in terms of a relation between people, and is expressed in simple symbolic notation. From this definition is developed a statement of power comparability, or the relative degree of power held by two or more persons. With these concepts it is possible for example, to rank members of the United States Senate according to their “power” over legislation on foreign policy and on tax and fiscal policy.

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The authors have developed a technique to estimate input functions from a population-based arterial blood curve in positron emission tomography (PET) studies with fluorine-18 fluorodeoxyglucose (FDG). A standardized pump injection was used in 34 subjects. A population-based blood curve was generated based on the first 10 subjects. In the remaining 24 subjects, an estimated input function (EIFa) was obtained by scaling the population-based curve with two arterial blood samples, one obtained at 10 minutes and the other at 45. Time integrals for EIFa and the real arterial input function (RIF) were in excellent agreement (r = .998, P < .0001). Cerebral metabolic rates for glucose calculated with EIFa and RIF and the autoradiographic method also correlated excellently (r = .992, P < .0001). Analogous correlations were achieved with arterialized venous samples as scaling factors. These results suggest that individually scaled, population-derived input functions may serve as an adequate alternative to continuous arterial blood sampling in quantitative FDG-PET imaging.

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