The role of structural and functional imaging in parkinsonian states with a description of PET technology.

In this article, after providing a description of the technique of brain positron emission tomography (PET), the review focuses on the application of PET and other recent advances of neuroimaging in understanding the structural, pathophysiological, and pharmacological changes associated with Parkinson's disease (PD). In early cases of PD, demonstration of the presence of nigral structural abnormalities with transcranial sonography and striatal dopaminergic dysfunction with functional imaging provides a rationale for the use of dopaminergic medications. The presence of altered striatal signal with diffusion-weighted magnetic resonance imaging (DWI) or reduced lentiform nucleus glucose metabolism with fluorodeoxyglucose PET suggests the presence of an atypical PD variant. Finally, the value of functional imaging as a biomarker for following the progression of PD and for understanding mechanisms of dementia when present is debated.