The histological assessment showed that Nissl-positive or TH-positive neurons within the SN were colocalized with pigmented NM. The densities of these histological components were positively correlated with one other but not necessarily with the density of the iron pigment (Supplementary Table S2). Significantly reduced (P < 0.0001) mean T2* values were observed for both iron pigments and NM with respect to the reference SN tissue region as shown in the T2* histogram for both subjects (Fig. 3). Iron pigments and NM showed similar mean T2* values. We observed that the T2* values were well correlated with NM in the ROI-SNc (Table 1). The Pearson’s partial correlation coefficient was higher for subject II (r = −0.47 for subject I, P < 0.0001 and r = −0.65 for subject II, P < 0.0001). T2* values were also significantly correlated with iron pigments within the ROI-whole SN, ROI-SNc, and ROI-SNr in both subjects (Table 1; P < 0.0001). Note that both Pearson’s linear correlations and nonparametric Spearman’s rank correlations yielded similar results. Coefficients of the multiple correlation (R) between T2* values, iron pigments, and NM were 0.56 and 0.70 for subject I and subject II, respectively. When β1 is for NM and β2 is for iron in each subject, respectively, subject I was found to have β0 = 10.83, β1 = −0.43, and β2 = −8.05 while subject II had β0 = 11.95, β1 = −0.83, and β2 = −12.64. Both cases had higher β-values for iron than NM. Considering that β1 indicates the contribution of NM to T2* and β2 is the contribution of iron to T2*, the relative contribution of iron to T2* is higher than the contribution of NM to T2* by a factor of 18.7 and 15.2 times for subjects I and II, respectively. In other words, one particle of iron confers about −10 (ms) to the T2* value of corresponding region, while 15 particles of NM confer about −10 (ms) to the T2* value of the corresponding region. However, mean T2* values in Fig. 3 were similar in both iron and NM pigments since the number of NM particles was much larger than that of iron particles from Perl-stained slides.