It's also worth noting that ADHD, as a condition, is mostly a Gordian knot of maladaptations. Built up over childhood (and beyond). While there are a lot of commonalities, you need to do a detailed investigation to pick out what bits are a problem to the individual.

If you're going to go through that process, then you might as well not tie up an MRI machine for no reason.

Drugs can treat the base problem, but don't work well without the follow-up care to repair the behavioural damage.