Receiver operating characteristic curves for various potential biomarkers of central dopamine (DA) deficiency. (A) Data from putamen:occipital cortex (PUT:OCC), caudate (CAU):OCC, and substantia nigra (SN):OCC ratios of 6-[18F]fluorodopa-derived radioactivity; (B) Data from cerebrospinal fluid neurochemistry (dihydroxyphenylacetic acid (DOPAC), DOPA, and dopamine (DA)). (C) Data for cardiac 6-[18F]fluorodopamine-derived radioactivity (FDA), University of Pennsylvania Smell Identification Test (UPSIT) scores, and UPSIT categories; (D) Date for putamen (PUT):substantia nigra (SN) and caudate (CAU):SN ratios of 6-[18F]fluorodopa-derived radioactivity; (E) Data for plasma levels of dihydroxyphenylglycol (DHPG), norepinephrine (NE), and dihydroxyphenylacetic acid (DOPAC). Dashed lines show sensitivities more than 50% at 1 – specificity of 20%.