Dat scan test result appointment

Can anyone advise on interpreting the Dat Scan test result?
I should imagine the neurologist shows you the images and points out the dopamine area and says if they think it is low or not. Are they just looking at a quantifiable volume/measurement of dopamine levels in the basal ganglia?
I am wondering, is it a given that if you have low dopamine levels therefore you will get Parkinsonian symptoms, or are there people with low dopamine that function quite normally/not show symptoms?

Also, any advice on what questions you would ask at this appointment? In my appointment letter the neurologist refers to discussing my treatment, so I would like to get as much information from this short important appointment as is possible.
Any advice gratefully received.
Kind regards