Spatial gradients of nigral magnetic susceptibility in de novo and medicated Parkinson's disease.

OBJECTIVES: Aberrant iron accumulation in the substantia nigra (SN) is implicated in Parkinson's disease (PD), but spatial gradients of magnetic susceptibility (χ) in PD remain unclear. This study aimed to quantify χ gradients of the SN across different stages of PD. METHODS: Twenty-one de novo PD (dnPD) patients, 27 medicated PD (mPD) patients and 29 healthy controls (HCs) underwent multi-echo gradient-echo MRI. Quantitative susceptibility mapping (QSM), paramagnetic (χpara) and diamagnetic (χdia) components were obtained using the APART-QSM algorithm. The bilateral SN were segmented into equally spaced subregions along three main axes to assess χ gradients. RESULTS: For dnPD patient, χ gradient changes manifested as elevated QSM and χpara values in the anterior and ventral right SN, accompanied by increased χdia values in the anterior and dorsal parts of the left SN, as well as in the middle segment of the right SN, compared to HCs. In the mPD group, higher QSM and χpara values were observed in the posterior and ventral parts and along the lateral-medial axis of the bilateral SN compared to HCs. Additionally, mPD patients exhibited left-right asymmetry in QSM and χpara in posterior SN regions compared to HCs. CONCLUSION: This study revealed spatially varying changes and asymmetries in nigral χ across different stages of PD, deepening the understanding of nigral pathology and demonstrateing potential for early diagnosis and severity assessment of PD.