Oh, yes, my brain has been MRI'd three times.  The first I had one small lesion, the second, a few teensy ones they said might be age related, and my most recent had none.  My demyelenation is in two places in my cervical spine, so if there is anything going on in the brain to affect the sense of smell, it's not large enough to show up yet.  No foods affect my ability to breathe.  I am not diagnosed with MS, although it is still a possibility.  Right now it's just transverse myelitis.

Mostly it's my very sensitive sense of smell, making me smell things no one else does.  But once in a while, there's no possible other source, like smoke clinging to someone's clothes, or a poopy smell that comes from nowhere.