The lack of in vivo biomarker(s) reflecting Parkinson's disease (PD)-related cell loss and associated pathoetiological/physiological processes in nigrostriatal structures has hindered discovery research and limited the ability to evaluate disease-modifying therapies. Recent research has generated excitement for using DTI and R2* MRI measures as biomarker(s) for PD-related pathology in nigrostriatal pathways, but they fall short by the lack of understanding of their clinical implications and biological/pathological underpinnings. Working closely with the National Institute of Neurological Disorders and Stroke (NINDS) Parkinson's Disease Biomarkers Program (PDBP), the proposed work will investigate multimodal MRI techniques in combination with fluid-based iron (Fe) protein profiles to serve as in vivo markers for PD-related nigrostriatal pathology that can be used as biomarkers for diagnosing PD, following its progression, and gaining mechanistic understanding of PD pathoetiology and pathophysiology.