Increased iron-related MRI contrast in the substantia nigra in Parkinson's disease.

Elevated iron levels in the substantia nigra (SN) of the brain in Parkinson's disease (PD) may mediate lipid peroxidative reactions, promoting SN neuronal death. To assess SN iron accumulation in living PD patients and its relation to motor performance, we measured, in 13 nondemented PD patients and 10 normal control subjects, simple reaction time (SRT) and simple movement time (SMT), followed by head MRI in a 3-tesla system. We measured T2 and T2* in the right and left SN of all subjects and calculated R2', the relaxation rate due to local magnetic field in-homogeneities, from these values. Asymmetries of 1/T2 (R2), 1/T2* (R2*), or R2' versus asymmetries of SRT and SMT were assessed in eight PD subjects who had not taken anti-PD medication(s) for 12 hours. The average of right and left SN values for R2 was lower, and R2* and R2' were higher, in PD patients than in controls (R2, p = 0.046; R2*, p = 0.001; R2', p < 0.001). R2' best predicted group differences. The asymmetry of SRT performance was highly correlated with asymmetries of SN R2* (0.91; p = 0.001) and R2' (0.72; p = 0.03). These results strongly suggest that the increases in iron levels seen postmortem in the SN in PD are reflected in increased iron-related MRI contrast at 3 tesla in living PD patients. Correlations with motor performance in PD suggest that the clinical severity of PD may be related to SN iron accumulation.

Preliminary observations of transverse relaxation rates obtained at 3 tesla from the substantia nigra of adult normal human brain.

The transverse relaxation rates R2 and R2* were measured at 3 T in the substantia nigra of the midbrain of adult normal human controls. The relaxation rate arising from magnetic inhomogeneities, R2', was calculated from the relationship R2* = R2 + R2'. No significant differences were found for any parameters between left and right side substantia nigra regions, however, a significant inverse correlation was found between R2 and R2' (r = 0.70, p = 0.035). Water diffusion, in the presence of paramagnetic metal ions, may play a role in determining the relative contributions to reversible and irreversible transverse relaxation and may explain the inverse correlation demonstrated here.

Assessment of relative brain iron concentrations using T2-weighted and T2*-weighted MRI at 3 Tesla.

In this paper a new method is presented for the relative assessment of brain iron concentrations based on the evaluation of T2 and T2*-weighted images. A multiecho sequence is employed for rapid measurement of T2 and T2*, enabling calculation of the line broadening effect (T2'). Several groups have failed to show a correlation between T2 and brain iron content. However, quantification of T2', and the associated relaxation rate R2', may provide a more specific relative measure of brain iron concentration. This may find application in the study of brain diseases, which cause associated changes in brain iron levels. A new method of field inhomogeneity correction is presented that allows the separation of global and local field inhomogeneities, leading to more accurate T2* measurements and hence, T2' values. The combination of T2*, and T2-weighted MRI methods enables the differentiation of Parkinson's disease patients from normal age-matched controls based on differences in iron content within the substantia nigra.