The acronym SWEDDs (scans without evidence of dopaminergic deficits) arose from the clinical trial literature for Parkinson’s disease (PD) [1]. Trials of l-dopa versus pramipexole (CALM-PD [Comparison of the Agonist Pramipexole with Levodopa on Motor Complications of Parkinson’s Disease]) [2] or ropinirole (REAL-PET [ReQuip as Early Therapy vs. l-dopa – Positron Emission Tomography]) [3] and a trial of l-dopa versus placebo (ELLDOPA [Earlier Versus Later Levodopa Therapy in Parkinson’s Disease]) [4] imaged patients with 18F-dopa PET or β-CIT single photon emission computed tomography (SPECT) in order to monitor disease progression (see Table 1 for commonly used molecular imaging techniques). This approach revealed a substantial proportion of clinically diagnosed cases of PD where there was no scan corroboration of that diagnosis; approximately 4–15% of clinically diagnosed cases of PD had no scan corroboration and were thus designated as SWEDDs. The very high number of normal molecular imaging scans in these studies was at odds with the demonstrably excellent clinical accuracy rate in post mortem series such as that of Hughes et al., in which the positive predictive value for the diagnosis of PD was 98.6% [5].