What specific head injuries were they looking for, and why didn't you tell them or your parents tell them you had a CI? There are other ways to diagnose problems without risk to the CI. Even if they had to proceed to the MRI, your doctor should have been informed that you were implanted. If he wasn't, then that's your parents fault for not informing the medical staff beforehand.
Tacha! That kind of information is extremely important--it's not like you or the parents forgot, Vol, that you had a CI.