echography vs tomography

echography and tomography both are nouns.

Word	Noun	Adjective	Verb	Adverb
echography	Yes	No	No	No
tomography	Yes	No	No	No

As nouns, tomography is a hypernym of echography; that is, tomography is a word with a broader meaning than echography:

echography: using the reflections of high-frequency sound waves to construct an image of a body organ (a sonogram); commonly used to observe fetal growth or study bodily organs
tomography: (medicine) obtaining pictures of the interior of the body

Other hypernyms of echography include prenatal diagnosis, imaging.

echography (noun)	tomography (noun)
using the reflections of high-frequency sound waves to construct an image of a body organ (a sonogram); commonly used to observe fetal growth or study bodily organs	(medicine) obtaining pictures of the interior of the body