MRI with contrast of arm. IV in hurt arm or other arm?

Yes, it will hurt. Ask before if the contrast is radioactive iodine. They say it will not harm but I personally think, they are devilish monstrous liars which are stupid like hell. Radioactive Material whatever made of has nothing!!! to do in the body. I mean, if you use tooth paste with fluoride, your thyroid is blocked anyway - lead to Hashimoto and all kinds of diseases which are connected with lack of iodine...if the Holocaust doctors are injecting radioactive iodine, it goes to your thyroid and to other Organs. You all can read that by research but you are not even interested what "doctors" do with your health (not especially meant you, asker but other user) It seams to me that many people are suicidal to get a treatment which are logically harmful.

It gets injected wherever it gets injected.

Bend over and drop your drawers