Water molecules are the most abundant molecules in the human body, so these are the very molecules the MRI machine uses to create an image. Water molecules consist of oxygen and hydrogen atoms, and the core of a hydrogen atom-its nucleus-is a single proton. Protons have a basic, inherent property called nuclear spin causing them to spin like a gyroscope or a top. Because the protons also have an electrical charge, the spin makes them act like tiny magnets. A magnetic field, which is measured in Tesla (T), will make these spinning protons wobble, like a spinning top that isn’t quite vertical. The stronger the magnetic field, the faster the wobble.