How painful is back MRI procedure?

Not likely. The MRI process is essentially painless. The only real discomfort involves staying still on a hard table for the duration of the study.
MRI causes no pain. And if you are smart you can ask your MRI facility how long does the average back MRI (lumbar) take. You will be surprised the answer is anywhere from 10 to 60 minutes. You will be happier if it is shorter for the routine scan. We can do a lumbar or cervical MRI in 10-12 minutes total scan time.