What medication should be given prophylactically to adult patients with a true history of contrast allergy?

There is a choice among two oral regimens and one IV regimen:
1. Methylprednisolone 32 mg orally 12 and 2 hours before the procedure
2. Prednisone 50 mg orally, 13, 7, and 1 hour prior to injection

3. Methylprednisolone (Solu-Medrol) 50 mg IV - 13, 7, and 1 hour prior to injection

The addition of diphenhydramine 50 mg orally 0r 25 mg. IV 1 hour prior to injection is beneficial.
If the prior reaction was severe, these questions must be considered: Does the patient really need this study? Are other modalities equally sensitive for the diagnosis (e.g., ultrasound, MRI)?