I’ve had a number of MRI scans but noticed no after effects either good or bad. In fact I was so comfortable that if it weren’t for the infernal noise I could have happily dozed off in the machine. I have heard of some people who find them claustrophobic and I once worked with someone who was too large to fit in!
I was far more uncomfortable in a CT Scanner where they used it to accurately place a needle for an injection into my spine.