Statistical analysis

To compare the differences in age and sex distribution between the patients with PD and normal controls, independent samples t-test and the Pearson χ² test were used. To evaluate the inter-observer reliability of the QSM and R2^* measurement by two neuro-radiologists, the intra-class correlation coefficient (ICC) was calculated. An ICC>0.81 was considered for excellent agreement; 0.61-0.80, good agreement; 0.41-0.60, moderate agreement; and <0.40, poor agreement. The normality of the data was analyzed using the Kolmogorov-Smirnov test. Measurement data were expressed as mean ± standard deviation. The group differences in the regional susceptibility and R2^* values between patients with PD and normal controls were compared using an independent samples t-test. When significant differences were found between the two groups, the diagnostic characteristics of QSM and R2^* mapping were analyzed for the corresponding region using receiver operating characteristic (ROC) curves. A correlation analysis between susceptibility and R2^* values and clinical features in patients with PD was performed. Pearson's correlation analysis was also utilized to investigate the correlation between the average susceptibility or R2^* values in each targeted region for all the normal controls in the present study, and the mean iron concentration in the corresponding regions of normal individuals determined in a previous post-mortem study (13). P<0.05 was considered to indicate a statistically significant difference. SPSS v13.0 (SPSS, Inc.) was used for all statistical analyses.