What this paragrargh means in MRI?

Question

In the case of hydrogen protons the excess in the lower energy state is only 0.0001% but that is enough.

In an applied magnetic field of 1.5 Tesla for every 2 million protons there are 9 more protons aligned with the applied field than there are against it.

Answer 1

Oh boy the joys of mrI physics.   This is this is about net magnetization.  I hope that you understand that the little protons in the nucleus of the hydrogen molecules act like small magnets spinning around.  When exposed to the magnetic field the want to line up with the field.  Now some of the protons are in a more excited state than the others and they want to line up facing backwards like the pt being feet first the lower energy protons want to line head first.  Now the feet first magnetic moments cancel the energy of the head first, fortunately the just like exams there are more head first than feet first leaving some uncanceled energy to use for measuring and creating images.  Now if you want to know why the protons want to go in feet first, you will have to find a physicist because I have decided to just take it as face value.  Understanding that there is a net magnetization is what is important for the sake of dealing with MRI questions.  See the site below for animated graphics.