variousparker,
You can have a MRI on just about every part of your body, depending on what the doc ordering the tests are looking for. For instance, my neuro ordered a brain and c-spine MRI because he was looking for MS lesions, they mostly occur in the brain, but can be found in the c-spine or thoracic area also. They usually do the c-spine because if there is a lesion located there it would short circuit from there down, so anywhere there is a lesion, it can control from that area downward. I myself have had 3 MRIs done, 2 of the brain, and 1 c-spine, everything was normal except both brain MRIs a year apart from each other showed sinus infection, worse this year, and my c-spine showed a bulging disk at C-3.
Contrast is used to show any new lesions. The old ones don't show up with contrast, but new ones do.
Hope this helps.