Renal localization of two${}^{99{\rm m}}{\rm Tc}\text{-labeled}$ radiopharmaceuticals,${}^{99{\rm m}}{\rm Tc}\text{-dimercaptosuccinate}$ and${}^{99{\rm m}}{\rm Tc}\text{-glucoheptonate}$, 1 hr after injection into rats, was studied using frozen section microautoradiography and macroautoradiography (X-ray film autoradiography). The distribution of both compounds was identical within each method, but the patterns of localization between the methods were discordant. Microautoradiographs showed a well-defined and regionally specific pattern of localization in the inner renal cortex, whereas macroautoradiographs demonstrated localization throughout the cortex. In the microautoradiographs the label was found principally over the cytoplasm of proximal tubule cells. Resolution and efficiency data were determined using autoradiographs of radioactive discs. The value for resolution was 2.3 μm and that for efficiency 11%. The radiation dosage experienced by microscopic structures after labeling with${}^{99{\rm m}}{\rm Tc}\text{-radiopharmaceuticals}$ can be calculated from autoradiographs if the efficiency is known.

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