Proton Relaxation
After being excited out of the equilibrium state by a radiofrequency pulse, the protons will begin to relax back to their equilibrium state. This process is typically described by two different kinds of relaxation: longitudinal (T1) relaxation and transverse (T2) relaxation.
Longitudinal (T1) Relaxation
Longitudinal relaxation refers to relaxation along the direction of the magnetic field. Longitudinal relaxation is also referred to as spin-lattice relaxation because energy is released into its surroundings, or lattice, allowing the proton to return to its equilibrium state.