@vijay26
A DAT scan is not invasive, it is a nuclear medicine scan performed in a radiology center. A "tracer" (a safe radioactive isotope drug) is injected into your arm and travels through your blood stream. It binds to dopamine (transporters) an can be seen in your brain by the nuclear medicine equipment which is positioned close to your head. This allows doctors to see how much dopamine is produced by your brain and can determine if you have a deficiency of dopamine indicating whether you have Parkinsons.
Hope this helps, Joe