MRIs use protons, which are abundant in the human body. All protons spin creating a small
magnetic charge. When a strong magnetic field is introduced, as is the case in an MRI machine,
the protons align with that field. The MRI technician then introduces a radiofrequency
pulse that disrupts the proton and forces it into either a 90 degree or 180 degree realignment
with the static magnetic field. Since the radiofrequency pulse pushed the proton against
its nature, once this pulse is turned off, the protons realign with the magnetic field,
releasing electromagnetic energy along the way. The MRI is able to detect this energy,
and is able to differentiate various tissues based on how quickly they release energy after
the pulse is turned off.