i haven't heard of mri giving people headache before, but it sounds yuck.
this will sound wierd, and i don't know exactly what kind of headache you have or which exact kinds this trick works for, but ... have you tried the pressure points in your hands, for a bit of relief?
i just went looking for an example of what i've used in the past - i don't know anything about the site i've grabbed this from, it just looks like what i've used on some headaches in the past:
Name: Hoku or Joining of the Valleys (Large Intestine 4)
Location: On the top of the hand, on the web where the thumb and the index finger meet. (See the red dot on the hand in the photo.)
To hold: Squeeze the point by putting your thumb on the point, and your index finger on the palm side of your hand. Make small circular motions with your thumb until you feel the point; it is tender on many people.Make sure that the hand that is holding the point is relaxed. The demo photo above shows you how to hold the point, but the hands are a little tense; the second photo, on the right, shows you the hands relaxed, which is how you want to do it.
Hold for 10 or 15 seconds initially, until you figure out what works for you. You can hold for a few minutes, but make sure that the holding hand does not get tense or tired out. Release gently if you feel any acute pain.
This is a wonderful point. It is effective for relieving so many discomforts, including headaches, constipation, insomnia, stress, shoulder and neck tension.
if it doesn't work on one side, try the other side. it's usually one or the other, not both. for me it works best on headaches in the forehead and temples. it's not a panacea really, but a bit of help. when you let go it will probably come back, unless it's ready to be gone anyway.