Background Parkinson’s disease (PD) is marked pathologically by dopamine neuron loss and iron overload in the substantia nigra pars compacta. Midbrain iron content is reported to be increased in PD based on magnetic resonance imaging (MRI) R2* changes. Because quantitative susceptibility mapping is a novel MRI approach to measure iron content, we compared it with R2* for assessing midbrain changes in PD. Methods Quantitative susceptibility mapping and R2* maps were obtained from 47 PD patients and 47 healthy controls. Midbrain susceptibility and R2* values were analyzed by using both voxel-based and region-of-interest approaches in normalized space, and analyzed along with clinical data, including disease duration, Unified Parkinson’s Disease Rating Scale (UPDRS) I, II, and III sub-scores, and levodopa-equivalent daily dosage. All studies were done while PD patients were “on drug.” Results Compared with controls, PD patients showed significantly increased susceptibility values in both right (cluster size = 106 mm3) and left (164 mm3) midbrain, located ventrolateral to the red nucleus that corresponded to the substantia nigra pars compacta. Susceptibility values in this region were correlated significantly with disease duration, UPDRS II, and levodopa-equivalent daily dosage. Conversely, R2* was increased significantly only in a much smaller region (62 mm3) of the left lateral substantia nigra pars compacta and was not significantly correlated with clinical parameters. Conclusion The use of quantitative susceptibility mapping demonstrated marked nigral changes that correlated with clinical PD status more sensitively than R2*. These data suggest that quantitative susceptibility mapping may be a superior imaging biomarker to R2* for estimating brain iron levels in PD.

Background-Recent magnetic resonance imaging (MRI) studies suggest increased transverse relaxation rate (R2*) and reduced diffusion tensor imaging (DTI) fractional anisotropy (FA) values in the SN in PD. The R2* and FA changes may reflect different aspects of PD-related

Background The pattern of dopamine cell loss in Parkinson's disease is known to be prominent in the ventrolateral and caudal substantia nigra, but less severe in the dorsal and rostral region. Both diffusion tensor imaging and R2* relaxometry of the substantia nigra have been reported as potential markers for Parkinson's disease, but their relative ability to mark disease progression and differences in pathophysiological bases remains unclear. Methods High resolution T2-weigthed, R2*, and diffusion tensor imaging were obtained from 28 controls and 40 Parkinson's disease subjects [15 early-stage (disease duration≤1 year), 14 mid-stage (duration 2-5 years), and 11 late-stage (duration>5 years)]. Fractional anisotropy and R2* values in both rostral and caudal substantia nigra were obtained for all subjects, and clinical measures (disease duration; levodopa-equivalent daily dosage; “off”-drug Unified Parkinson's Disease Rating Scale motor score) were obtained for Parkinson's subjects. Results There was no correlation between fractional anisotropy and clinical measures, whereas R2* was strongly associated with disease progression. Compared to controls, fractional anisotropy in caudal substantia nigra was significantly decreased in Parkinson's disease patients of all stages, whereas in rostral substantia nigra it was decreased significantly only in the late-stage group. R2* in both substantia nigra regions was significantly increased in the mid-stage and late-stage, but not early-stage, of Parkinson's disease subjects. Conclusions These findings suggest that fractional anisotropy changes may mark early pathological changes in caudal substantia nigra, whereas the changes in R2* may more closely track Parkinson's disease's clinical progression after symptom onset.