I'd be careful about this. I've never seen anything to suggest that we could screen every child with FMRI scans to catch blatantly obvious indicators of ADHD or use scans as a definitive test for who should get medications. I honestly wish it really worked that way because it'd end all the hand-wringing about overprescribed medications and prevent a lot of kids from struggling unnecessarily, but unless something's changed pretty recently there's no one test that identify someone with ADHD.