But, the package of energy which each of these nuclei can accept is different than the package size the hydrogens take, so, they will not jump to a higher energy level when zapped with the radiowaves, and hence will not give off radiation. Most of the signals in an MRI scan originate from the hydrogens of water molecules, because these hydrogens are far more abundant in tissues than are the hydrogens of organic compounds. The difference in the way water is bound in different tissues is what produces much of the signal variation among the organs as well as the signal variation between healthy and diseased tissue. 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.