Hi, I'd like to help you with your question.
This is a frequent problem with MRIs so you are not alone. Since medication is not an easy option for you, you may want to try therapy. Although most people tend to feel therapy is not an easy answer, it is actually the most effective. Medication can reduce symptoms, but it cannot eliminate the phobia. Once the medication is stopped, the phobia is still there. Therapy can work to help you understand your fear and find ways to rid yourself of the symptoms once and for all. You do this by working on how you think about your fear and changing your thought processes so you no longer respond the way you do now.
You mentioned that you will eventually need an MRI so I am guessing you may have time for some short term therapy and self help. The good news is that phobias are one of the easiest problems to treat. Cognative behavior therapy (CBT) has been shown to help and is very effective within a short period of time. To find a therapist, contact your doctor for a referral. Or you can search on line at http://therapists.psychologytoday.com/rms/.
You can also help yourself. Here are some resources to get you started:
The Anxiety & Phobia Workbook by Edmund J. Bourne
Anxiety, Phobias, & Panic: A Step-by-Step Program for Regaining Control of Your Life by Reneau Z. Peurifoy
The Cognitive Behavioral Workbook for Anxiety: A Step-By-Step Program by William Knaus and Jon, Psy.D. Carlson
You can find these books on Amazon.com or your local library may have them for you.
Let me know if I can help any further,