In nuclear medicine imaging, an organ's blood flow or particular function is assessed by visualizing the in vivo distribution of radioactive tracers. Various pathological states lead to spatial or temporal changes in the distribution of these tracers. Since the presence and degree of such pathological changes are usually evaluated visually, image interpretation may be biased to some extent by the interpreter's subjective criteria. In order to make image interpretation more objective, a quantitative approach based on modeling of tracer kinetics has been applied to many nuclear medicine studies, utilizing numerical data derived from digital images. In this brief report, the basic concepts and procedures for kinetic modeling analysis are introduced. As an example of compartment model analysis, classical 2-compartment model analysis using plasma data for two renal blood flow agents (Tc-99m-MAG3 and l-131-OIH) is performed to compare the distribution and elimination kinetics of these tracers. To better understand the tissue distribution of blood flow tracers, the basic concept of blood flow and tissue clearance is introduced based on a tissue blood flow model. In addition, graphical analysis and its application to Tc-99m-HMPAO are discussed as a simple method for determining tissue clearance. These kinetic analyses are quite simple, but the application of this method to various tracers could result in the identification of quantitative parameters that are clinically useful in the field of nuclear medicine.
