I am not aware of any afirmative tests and/or scans that can diagnosis PD. Even O15 Pet scans are still not generally accepted.
I am now 43 with yopd since 1998 and staying active and postive has been my most successful treatment. Always plan your day so that you feel rewarded by setting achieveable fitness / activity goals.
Dopamine (L-dopa) is primarily used (consumed) in large muscle groups during the five step biosynthesis of adrenaline. And in the limbic system of the brain which is the flight or fight, risk and reward center.
Reward and motivation to the Parkie is like a transmission is to a car: even with full tank of dopamine (hi grade gas), without a transmission the engine shakes, races and floods but cannot initiate movement. This is why Sinemet typically does not work by itself. It needs an agonist such as requip, mirapex to override the transmission and bypass the risk and reward system. Hence most high dose agonist users seek reward without reason and can be reported as demented or can become gamblers, shopaholics and workaholics...