DDC and Parkinsonism: No diagnostic accuracy studies have compared the efficiency of the PET tracers directly for diagnosing Parkinsonism, but a meta-analysis of 142 PET studies reports a consistently smaller PD-related decrease in tracers targeting the dopa decarboxylase such as [18F]FDOPA, as compared to tracers targeting the dopamine transporter or vesicular monoamine transporter [43] and thus suggests a smaller effect size for discrimination between PD and healthy controls using [18F]FDOPA compared to [18F]FE-PE2I PET.