I did note this:

Brain imaging is not ready for use as a diagnostic tool in ADHD, Shaw said."It is still too early to use neuroanatomical scans for diagnosis," he said. "We had to scan hundreds of children to identify subtle differences. They [the differences] are very real, but they are subtle. So the scan of any one child will not tell you a great deal about whether [he or she has] ADHD or not. Currently, the diagnosis of ADHD remains clinical."

http://www.psychiatrictimes.com/articles/brain-maturation-de...

A buddy of mine was telling me that you could diagnose ADHD with brain scans--this link seems to say the exact opposite.