PET/MR Imaging in Patients With Short and Long Standing Parkinson's Disease

Parkinson's disease (PD) is a chronic, progressive, neurodegenerative disease that affects 1% of the population older than 60 years. The disease presents as a movement disorder manifesting mainly with resting tremor, bradykinesia, cogwheel rigidity and postural instability along with cognitive and behavioral disturbances and symptoms of other non-motor systems dysfunction. The pathophysiology of the motor dysfunction in PD is related to gradual loss of nigrostriatal dopaminergic neurons (originating from the substantia nigra (SN) compacta to the striatum) leading eventually to depletion of dopamine in the striatum. Striatal fluorine-18 isotopologue for L-3,4-dihydroxyphenylalanine(\[18F\] F-DOPA) uptake follows a typical spatiotemporal pattern along the course of disease starting with a decreased uptake in the dorso-caudal putamen (contralateral to the side of predominant motor involvement) that progress to the caudate nucleus. The role of traditional magnetic resonance imaging (MRI) in the evaluation of PD is aimed mainly to differentiate idiopathic PD from secondary parkinsonism (e.g. vascular) and from other degenerative but atypical parkinsonian syndromes (e.g.Progressive supranuclear palsy ( PSP), Multiple system atrophy (MSA) etc.) that are associated with distinct structural features and therefore help establishing the diagnosis. However, new MR sequences such as diffuse tensor imaging (DTI) and susceptibility-weighted imaging (SWI) are now being investigated to evaluate the nigrostriatal dopaminergic neurons and iron accumulation in the SN, respectively. Resting-state functional magnetic resonance imaging (fMRI) that depicts brain network organization has been shown to be altered in patients with PD. In this technique, temporally synchronous, spatially distributed, spontaneous low frequency blood-oxygen level-dependent signal fluctuations in task-free settings are further clustered into maps of functional large-scale neural networks. Lower network efficie