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Initial Concepts Production of a Magnetic Field When an electron travels along a wire, a magnetic field is produced around the electron (Fig 1).Hydrogen Protons It is necessary to have a source of hydrogen pro- tons (protons in the nuclei of hydrogen atoms, which are associated with fat and water mol ecules) in order to form our MR signal The hydrogen proton is positively charged and spins about its axis (like a child's spinning top).Main Magnetic Field The main magnetic field of an MR system comes from a large electric current flowing through wires that are formed into a loop in the magnet of the imaging system (Fig 3).The wires are immersed in liquid helium (at superconducting temperatures) so that very large currents can be used to produce the strong magnetic field.When an electric current flows in a wire that is formed into a loop, a large magnetic field will be formed perpendicular to the loop Resonance Resonance aids an efficient transfer of energy.This positively charged spinning proton acts like a tiny magnet (Fig 2).

Initial Concepts
Production of a Magnetic Field
When an electron travels along a wire, a magnetic field is produced around the electron (Fig 1). When an electric current flows in a wire that is formed into a loop, a large magnetic field will be formed perpendicular to the loop
Resonance
Resonance aids an efficient transfer of energy. This is true, for example, when pushing a child on a swing. The child will swing back and forth at a particular frequency. If we push the swing at the right time, we will efficiently transfer energy to the swing and child. If we consistently push at the right time, we will be in resonance with the swing, and the efficient transfer of energy will allow the child to swing higher.
Hydrogen Protons
It is necessary to have a source of hydrogen pro- tons (protons in the nuclei of hydrogen atoms, which are associated with fat and water mol ecules) in order to form our MR signal The hydrogen proton is positively charged and spins about its axis (like a child's spinning top). This positively charged spinning proton acts like a tiny magnet (Fig 2). The hydrogen protons in our body thus act like many tiny magnets.
Main Magnetic Field
The main magnetic field of an MR system comes from a large electric current flowing through wires that are formed into a loop in the magnet of the imaging system (Fig 3). A typical clinical MR sys- tem will have a magnetic field strength of 1.5 T (tesla) (1 T = 10,000 gauss). The wires are immersed in liquid helium (at superconducting temperatures) so that very large currents can be used to produce the strong magnetic field. The magnet can be "ramped" with a power supply (to inject electric current into the coils of wire), and the power supply can then be removed. The imaging system can retain this electric current for many years (with no need to inject additional electric current) with only minimal loss in electric current and minimal decrease in magnetic field strength. The liquid helium levels in the magnet will need to be filled at regular intervals (once per month to once every few years, depending on the magnet design)