Cerebral Metabolism of 6–[18F]Fluoro-l-3,4-Dihydroxyphenylalanine in the Primate

The tracers 6-18F]fluoro-L-3,4-dihydroxyphenylalanine (6-18F]fluoro-L-DOPA) and L-14C]DOPA were injected simultaneously into rhesus monkeys, and the time course of their metabolites was measured in the striatum and in the occipital and frontal cortices. In the striatum, 6-18F]fluoro-L-DOPA was metabolized to 6-18F]fluorodopamine, 3,4-dihydroxy-6-18F]fluorophenylacetic acid, and 6-18F]fluorohomovanillic acid. The metabolite pattern was qualitatively similar to that of L-14C]DOPA. 6-18F]Fluorodopamine was synthesized faster than 14C]dopamine. In the frontal cortex, the major metabolite was also 6-18F]fluorodopamine or 14C]dopamine. In the occipital cortex, the major metabolite was 3-O-methyl-6-18F]fluoro-L-DOPA. On the basis of these data, the images obtained with 6-18F]fluoro-L-DOPA and positron emission tomography in humans can now be interpreted in neurochemical terms.