X-ray picture vs shadowgraph

X-ray picture and shadowgraph both are nouns.

Word	Noun	Adjective	Verb	Adverb
X-ray picture	Yes	No	No	No
shadowgraph	Yes	No	No	No

As nouns, shadowgraph is a hypernym of X-ray picture; that is, shadowgraph is a word with a broader meaning than X-ray picture:

X-ray picture: a radiogram made by exposing photographic film to X rays; used in medical diagnosis
shadowgraph: a photographic image produced on a radiosensitive surface by radiation other than visible light (especially by X-rays or gamma rays)

Other hypernyms of X-ray picture include radiogram, radiograph, skiagram, skiagraph.

X-ray picture (noun)	shadowgraph (noun)
a radiogram made by exposing photographic film to X rays; used in medical diagnosis	a photographic image produced on a radiosensitive surface by radiation other than visible light (especially by X-rays or gamma rays)