MRI and mid-back imaging: what to expect?

Do they actually use contrast dye when they're doing an MRI on the mid-spine? I’ve got a nasty allergy to iodine, though I've heard they might not even use the same stuff for these scans, but just wanted to double-check for peace of mind.

In most instances, contrast isn't really utilized...
But regardless of the situation, you absolutely have to mention that you have allergies

Contrast isn't typically necessary, but even if it is, you won't have any issues. Since MRI contrast agents don't contain iodine, there's no risk of an allergic reaction for you.