Quantitative mapping of T1 and T2* discloses nigral and brainstem pathology in early Parkinson's disease

Quantitative magnetic resonance imaging is a promising in vivo imaging technique revealing insights into different aspects of brain morphology in neurodegenerative diseases based on the determination of physical tissue parameters. Using combined T1- and T2*-mapping, we investigated changes of local relaxation times in the midbrain and lower brainstem of 20 patients with early Parkinson's disease (PD) compared to 20 healthy controls. Voxelwise statistical parametric mapping disclosed a widespread reduction of midbrain T1 values contralateral to the clinically more severely affected limbs. Within the SN, the T1 decrease matched the known pattern of selective neuronal loss as examined in various post-mortem studies, suggesting that T1 is a marker for PD related tissue pathology. However, the spatial extent of T1 reductions exceeded the SN and reached non-dopaminergic areas in the pontomesencephalic junction potentially involved in early non-motor symptoms of PD. In contrast, T2*-mapping revealed a bilateral decrease of T2* values restricted to the SN, indicating a local increase in total iron content. We conclude that, particularly in longitudinal studies, quantitative T1 may be a valuable marker for the monitoring of progressive neuronal loss in PD, whereas nigral T2* reductions might be more closely associated with an increased general vulnerability for the development of the disorder.