MRI

Would it be possible to get an MRI on your shoulders with rods in your legs?
I think it's possible to have the MRI just work on your upper body and ignore you're lower body.
Would appreciate guidance.

No, you can’t since the fact even in the MRI room there is always a very strong magnetic field. You can check on google to see some pics of what happens when a metal thing like a chair  is introduced even just in the same room of the machine. When the machine is active the magnetic field is even stronger. Clearly it’s impossible to isolate your limbs so until you have nails you are not allowed to do this exam.
This rule is valid for every ferromagnetic metal, such as iron. I’m supposing that the nail is made by steel cause it should be present at least in a part of the nail, I don’t think that a nail made by no-ferromagnetic metal is available. For what concern the Nuvasive nail: precise stryde is made by steel; precise 2 is made by titanium (which is a no-ferromagnetic metal), however the internal mechanism is surely made by steel so I’m sure it’s not possible with this nail neither.

Unfortunately MRI is not like doing a CT or a Radiography. Radiations are precise and you can know exactly which part of the body will be involved, while magnetic fields are huge and I repeat, they are active even when the machine is turned off.