Multiple Sclerosis 101
The human body is mainly made of water and fat, and water is of course made up of hydrogen and oxygen (H2O). An MRI scan focuses on all of the hydrogen atoms within the body. Normally they are spinning around in random directions like a spinning top, but when you put a big powerful magnet next to them they snap to attention and align with the magnetic field. Next, pulses of radio frequency are applied which knock the hydrogen out of alignment with the magnetic field. The radio frequency is then shut off, and the hydrogen atoms snap back to attention once again.
- National MS Society: Managing Relapses http://www.nationalmssociety.org/Treating-MS/Managing-Relapses