Energy levels of nucleus in emitting radiation in MRI

[opfphysics]

Hi experts
please explain energy levels of nucleus in emitting radiation in MRI

 

[Parlyne]

MRIs don't emit radiation. They operate using an entirely magnetic effect.

 

[Drakkith]

The wiki article states: After the field is turned off, those protons which absorbed energy revert to the original lower-energy spin-down state. Now a hydrogen dipole has two spins, 1 high spin and 1 low. In low spin both dipole and field are in parallel direction and in high spin case it is antiparallel. They release the difference in energy as a photon, and the released photons are detected by the scanner as an electromagnetic signal, similar to radio waves.

I'm unsure just what they mean when they say it releases photons. Is it actually emitting radiation, or are the magnetic moments returning to their previous alignment and in the process the changing magnetic field inducing a detectable signal?

 

[granpa]

a magnetic dipole in a uniform external magnetic field will resonate at one particular frequency.