A study led by Xing, Lin, and Li identifies perivascular space fluid diffusivity, measured via advanced diffusion-weighted MRI, as a biomarker predicting Parkinson’s disease course in prodromal and early stages. These findings highlight disruptions in the brain’s glymphatic system involved in metabolic waste clearance, potentially enabling earlier diagnosis and prognostics. This novel imaging biomarker may guide personalized interventions before pronounced motor symptoms emerge.