MRI take home point (1)

• Atomic nuclei with either an odd number of protons or an odd number of neutrons have nuclear magnetic dipole moments.
• The signal in MRI results from the magnetic dipole moments of hydrogen nuclei.
• A strong magnetic field is needed to align hydrogen nuclear magnetic dipole moments preferentially along the magnetic field, the longitudinal direction.
• The larmor frequency is determined by the magnetic field strength and the nucleus of interest.
• Radio-frequency electromagnetic waves applied at the larmor frequency are used to flip the collective magnetization of tissue into the transverse plane where it can be measured.
• The precession of magnetic dipole moments around the direction of the magnetic field at the larmor frequency causes tissue magnetization to induce an alternating electric current in a nearby receiver coil, enabling signal measurement.