To have an MRI, the whole person must fit into a huge magnet and then lie very still for 45 minutes to 2 hours. You are able to speak through an intercom to the technician. Some people become quite claustrophobic. The instrument produces no harmful rays so the technician or family members can remain close by. During the scan, the magnet will effect anything metal, so you must not wear any jewelry or anything made of metal.
Some people say that their fillings tingle during the scan.
The magnetic is a superconducting magnet, cooled with liquid helium. As each separate image is scanned, the pulsing magnet bangs and thumps. Sometimes a contrast is injected to produce better pictures. The electromagnetic radiation used to charge the hydrogen atoms is much, much lower in energy and much less damaging than X-rays. There is no limit to the number of MRI scans a person can have.