You take off anything that contains metal: clothes, piercings, watches (they brake anyway in the room - magnetic field).
I've had 2 MRIs done -wrist and total spine and I must say, I fell asleep both times, even though you have these banging noises. But since they are rhythmic I find they sort of put you into trance the only thing is that the noise changes after a few minutes, usually just when you have got used to it.
One other thing: a CT basicly works with x-rays which gives you large doses if you take pics of the spine (bones). MRI has no such harmfull rays (magnet). As said above MRI shows soft tissue much better, x-rays are better for hard "tissue" such as bones. So looking at the ligaments or discs or spinal cord you need an MRI.