Once you have anxiety about a certain thing, will you always have it for that certain thing?

Anxiety is so mind boggling to me. I understand it to a degree, but if I really try to understand I get so confused. For instance, say someone never had an MRI before, they go in knowing nothing about it, and get through it fine. Years later they think about getting back into that machine, and they get all bothered by the thought. Is their a way to get back to the other way of just jumping into something, and not worrying about it and getting through it?