I have major issues with MRI's. I didn't know I was claustrophobic until I had to start having MRI's when I was being diagnosed. When I first started having to have the MRI's, I was given Xanax. They might as well given me candy because it did NOTHING for me.
The next step was to put me under anesthesia. That didn't go so well b/c they didn't give me enough and I woke up kicking and screaming, "Get me out of here". Even though I started moving around, it all worked out and the MRI turned out fine.
The next year I had to get one for an annual check up. By that time, I weight a bit over 300 lbs, and they told me I had exceeded the weight limit. The doctor then gave me the okay to do an open MRI.
By the next year, fortunately (but unfortunately) I had lost 60 lbs and was able to do the standard MRI machine again. They would not allow me to do the open MRI, b/c they said the pictures don't turn out as good. Luckily, they had updated their MRI machine and it now accommodates people up to 500 lbs, and it feels more like an open MRI machine. I also got lucky and they gave me Valium.
I also broke my MRI's up into 3 separate (head, neck, and spine). I knew that even with the Valium, I would not be able to stay still in an MRI machine for over 2 hours. Each MRI only lasted about 45 minutes, and with the Valium, it was the easiest MRI's I have ever had. I think I actually fell asleep b/c I was that relaxed.
Don't give up. It may take a few tries to find out what works for you. It is a trial and error thing (unfortunately).