A DATscan is not definitive for a diagnosis of PD. Nothing is really, anymore. It used to be the presence of Lewy Bodies (mangled dead cells and a misfolded protein or two), but that is now dubious as recent research indicates they may actually be protective.

I was recently rejected by the NIH for any PD research trials, so I had a DATscan which contradicted their clinical "undiagnosis". It can only conclude that you have cell loss that can be PD or another "neurodegenerative disease". That cost me $8,000 which I do not have. IMO, they don't know what we have.

The scans are used to differentiate between a diagnosis of Essential Tremor or other Parkinsonism like diseases such as Multiple System Atrophy (MSA), to my knowledge.