I have had several brain MRIs in the past 2 years since the mets were discovered in April 2017-do it every 3 months. Its very simple and not at all bothersome. In fact if small tumours show up they are easily controlled with the cyber knife treatment which is completely painless (I have done it twice). No side effects and feeling good.
I feel its better to know while the tumours are small as there are so many treatment options now.
Wish you all the best for your tests