This study investigates a new way to look at heart nerves with a special scan called **[18F]-MFBG PET**. It compares this scan to an older method, **[123I]-MIBG SPECT**, to see which is better at telling apart certain brain diseases. These diseases are **Parkinson's Disease (PD)**, **Multiple System Atrophy (MSA)**, **Dementia with Lewy Bodies (DLB)**, and **Alzheimer's Disease (AD)**. Participants will have to visit the hospital 3 to 4 times for different tests, including brain scans and heart scans. **Key Points:** 1. **Participation involves 3 to 4 hospital visits** for various scans and tests. 2. **No major health issues** like heart disease or diabetes, and participants must be non-smokers. 3. **Participants should be between 18 and 85 years old** and must understand and consent to the study. The study aims to see if the new scan can better distinguish between these diseases, possibly leading to earlier and more accurate treatment.