If there are risks, I'm afraid most of us on the board are in big trouble.
When in the midst of chronic back issues, it is not uncommon to have a number of MRIs per year. Insurance does not like to pay for more one about every six months, but when you start having various parts of your body done, it does add up! Oops, I see you are in Canada, so you don't have to deal with insurance companies.
Sorry I can't give you a factual answer. Hopefully someone else will know the science and can tell you the risk.