For intravenous contrast, MRI
uses gadolinium contrast whereas CT
uses iodinated contrast; there is no cross-reactivity between different classes of contrast media.* For oral contrast, this uses VoLumen (barium sulfate suspension), which rarely has allergic reaction.
While you should not have a contrast study if you had prior severe allergic reaction (e.g., anaphylaxis), you can still consider having a contrast study if you had prior mild to moderate allergic reaction (e.g.