Abstract
The purpose of the present study was to evaluate the potential of multimodal MR imaging including mean diffusivity (MD), fractional anisotropy (FA), relaxation rates R2 and R2* to detect disease specific alterations in Parkinson's Disease (PD). We enrolled 82 PD patients (PD-all) with varying disease durations (≤5 years: PD≤5, n = 43; >5 years: PD>5, n = 39) and 38 matched healthy controls (HC), receiving diffusion tensor imaging as well as R2 and R2* relaxometry calculated from multi-echo T2*-weighted and dual-echo TSE imaging, respectively. ROIs were drawn to delineate caudate nucleus (CN), putamen (PU), globus pallidus (GP) and substantia nigra (SN) on the co-registered maps. The SN was divided in 3 descending levels (SL 1–3). The most significant parameters were used for a flexible discrimination analysis (FDA) in a training collective consisting of 25 randomized subjects from each group in order to predict the classification of remaining subjects. PD-all showed significant increases in MD, R2 and R2* within SN and its subregions as well as in MD and R2* within different basal ganglia regions. Compared to the HC group, the PD≤5 and the PD>5 group showed significant MD increases within the SN and its lower two subregions, while the PD≤5 group exhibited significant increases in R2 and R2* within SN and its subregions, and tended to elevation within the basal ganglia. The PD>5 group had significantly increased MD in PU and GP, whereas the PD≤5 group presented normal MD within the basal ganglia. FDA achieved right classification in 84% of study participants. Micro-structural damage affects primarily the SN of PD patients and in later disease stages the basal ganglia. Iron contents of PU, GP and SN are increased at early disease stages of PD.
Highlights
Normal findings on neuroimaging were long regarded as a diagnostic prerequisite of classical Parkinson's disease (PD) [1]
After first reports on T2 signal decreases within the basal ganglia and substantia nigra in PD [3], the quantification of the iron-sensitive T2 and T2Ã signal has been established by calculating the relaxation times, which is commonly achieved by the read-out of several echos [4]
Since mean diffusivity (MD), fractional anisotropy (FA), R2 and R2Ã were not normally distributed, non-parametric tests were used for statistical evaluation
Summary
Normal findings on neuroimaging were long regarded as a diagnostic prerequisite of classical Parkinson's disease (PD) [1]. Magnetic resonance imaging (MRI) has been mainly employed for the exclusion of other pathologies causing symptomatic parkinsonism like brain tumors or cerebral ischemia [2]. The relaxation rates R2 and R2Ã are the reciprocal values of T2 and T2Ã relaxation times, respectively, and have been shown to correlate to the iron concentration within the brain tissue, as evaluated in a previous post mortem study [5]. This technique was employed for the assessment of iron deposition in PD and affirmed the prominent iron deposition within the substantia nigra [6,7,8]
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