I think myself nailed it, as usual: Your doc was probably trying to rule out lesions and such. In any case, you have every right to ask your doc about this and demand some answers.

This wasn't part of the original question, but since it came up: It seems like MRI's might be able to detect signs of schizophrenia, but only if a series are conducted over a long period of time. (A single image won't show it -- multiples are required so that a pattern of change can be detected.) Also, this seems more effective for early onset than later in the course of things. I only understand the bare essentials of MRI, though, so take everything I've said with a grain of salt.