MRI vs imaging

MRI and imaging both are nouns.

Word	Noun	Adjective	Verb	Adverb
MRI	Yes	No	No	No
imaging	Yes	No	No	No

As nouns, imaging is a hypernym of MRI; that is, imaging is a word with a broader meaning than MRI:

MRI: the use of nuclear magnetic resonance of protons to produce proton density images
imaging: (medicine) obtaining pictures of the interior of the body

Other hypernyms of MRI include tomography.

MRI (noun)	imaging (noun)
the use of nuclear magnetic resonance of protons to produce proton density images	(medicine) obtaining pictures of the interior of the body
	the ability to form mental images of things or events