The NY Times reports:

Doctors cannot diagnose attention deficit or any other psychiatric disorder with imaging technology

I've met people who have told me that their kid has ADD or autism or dyslexia or something else, and that they are sure of it because of an MRI or some other brain scan. It is just not possible with current technology.

The main point of the article is to say that misbehaving kids are not doomed:

Kindergartners who interrupted the teacher, defied instructions and even picked fights were performing as well in reading and math as well-behaved children of the same abilities when they both reached fifth grade, the study found. ... The findings should also put to rest concerns that boys and girls who are restless, disruptive or withdrawn in kindergarten are bound to suffer academically. ...

About 80 percent of those with attention problems were taking or had taken stimulant drugs, and the researchers did not know the effect of the medications on brain development. Doctors consider stimulant drugs a reliable way to improve attention in the short term; the new study is not likely to change that attitude.

So your kid will do fine without the drugs, but your pediatrician will want to drug him anyway.