Dopamine active transporter (DAT) with positron emission tomography (PET) scans of the brain of an 85 year old male patient. This scan is used to diagnose Parkinson's disease when a clinical assessment is not conclusive. It uses a radioactive tracer that binds to dopamine transporter molecules found on dopamine neurones (nerve cells) in the brain. Most of the dopamine neurones are in a central region of the brain called the striatum. In patients with Parkinson's disease only a small area of the striatum will be highlighted by the tracer as it is the death of the dopaminergic neurones that leads to the symptoms of Parkinson's disease. These symptoms include tremor, muscular rigidity, poor balance and depression.