  One of the must important non-invasive techniques in medicine is the Magnetic
Resonance Imaging (MRI), it is used to obtain information of the structure of
the human body parts using three dimensional images. The technique to obtain
these images is based by the emission of radio waves produced by the protons of
the hydrogen atoms in water molecules when placed in a constant magnetic field
after they interact with a pulsed radio frequency (RF) current, the spin of the
protons are in a spin excited state. When the RF field is turned off, the MRI
sensors are able to detect the energy released (RF waves) as the protons
realign their spins with the magnetic field.
  We used a three particles model for the water molecule: the two protons from
the hydrogen atoms move around the doubly negatively charged oxygen
(unstructured), to describe the total angular momentum. The energy levels from
the water molecule are studied in presence of an uniform external magnetic
field, which interacts with the proton's spin and orbital angular momentum. The
energy is shifted and the degeneration is lifted. To illustrate the results, we
provide numerical results for a magnetic field strength commonly used in MRI
devices.
