Fluorodopa ¹⁸F Other names: Fluorodopa (18F)

In dopaminergic nerve terminals in the brain, fluorodopa (FDOPA) F18 is decarboxylated by amino acid decarboxylase to fluorodopamine (FDA) F18 and stored in presynaptic vesicles in the brain. The accumulation of F18 FDA in the striatum is visually detected in the PET scan.

Optimal PET imaging is achieved between 75 to 90 minutes after administration of fluorodopa F18 injection based on its pharmacokinetics. The relationship between fluorodopa F18 dose and plasma concentration is not fully characterized.

Distribution

Following the intravenous administration, fluorodopa F18 is cleared from the blood with a biologic half-life of about 1 to 3 hours. The time course of “background” brain radioactivity after fluorodopa F18 was evaluated. F18 activity in the cerebellum was greater than the parietal or occipital cortex during the first 30 minutes after fluorodopa F18 suggesting regional differences in amino acid transport.

Elimination

Fluorodopa F18 is cleared from the blood and tissue within 24 hours.

Metabolism

Fluorodopa F18 is decarboxylated by aromatic amino acid decarboxylase in the striatum to fluorodopamine F18. Fluorodopamine F18 is also metabolized via monoamine oxidase to yield [¹⁸F] 6-fluoro-3,4-dihydroxyphenylacetic acid (¹⁸FDOPAC) and subsequently by COMT to yield [¹⁸F]6-fluorohomovanillic acid (¹⁸FHVA).

Elimination

80% of the radioactivity is eliminated through the urine. Urine radioactivity peaks at about 30 minutes post-injection. The radiation absorbed dose to the bladder wall is reduced by emptying the bladder just before scanning.