**Study Summary** This research study is examining a new tool called **[11C]SY08**, used in a type of brain scan called **PET imaging**. PET stands for *Positron Emission Tomography*, a special test that helps doctors see detailed images of the brain. The study aims to see how well this tool works in detecting a protein called **alpha synuclein (αS)**, which builds up in the brains of people with certain diseases like Parkinson's Disease (PD), Multiple System Atrophy (MSA), and Dementia with Lewy Bodies (DLB). Participants in the study will receive a small injection of [11C]SY08 and will have a PET scan to see how the substance spreads in the brain. **Key Points:** - The study is open to people aged 50-80, including both healthy individuals and those with PD, MSA, or DLB. - Participants will need to attend one PET/MRI scanning session; this can take up to 90 minutes. - The study is not suitable for those with certain health conditions or those who cannot safely undergo a PET scan. Participants must meet specific health criteria and should not have recently had major surgery or certain psychiatric conditions.