MRI's are expensive (in the US). Specialist mental health care is not covered under most standard health insurance plans. How about you just fill out the questionnaire[1], and we'll match you with a nice (newly patented) pill?

[1] http://www.depressedtest.com

See also: Questionable sponsorship of online depression tests.

http://www.policymed.com/2010/02/letters-from-grassley-quest...

> What about correlations with patterns in MRI scans?

An excellent question, about which I know absolutely nothing.

Something to keep in mind, though: medical tests & whatnot are only useful insofar as they affect the way we handle treatment. Diagnosing depression really isn't that tough; if someone has a debilitating mood disorder, then it is reasonable to get them some kind of help. (I imagine that, for some of these people, the really hard problem is getting them to figure out they have troubles that the medical establishment can help with.)

So I don't think we need MRIs to tell whether someone is depressed. OTOH, can MRIs tell us what treatments are likely to be successful? That sounds like a very interesting question. Hopefully, someone is looking into it.