Sony 7506. Have a single pair that I used for countless symphony recordings, mixes, and just using around the house when I want to hear something special. Replaced the ear cups many times, and perhaps they aren't as bright as they were 20 years ago, but higher frequencies start dropping off a man's hearing around age 30. Great for using when reference/clarity matters, but will cause some fatigue after a couple of hours for me. Cheapo $20 earbuds with a rechargeable case have changed the game for me, I wear them everywhere.

All MRI machines have fans now, as some scans (such as your lower back) tend to heat you up. Ask the technologist to turn it on beforehand if you know it will relax you.