encephalogram vs roentgenogram

encephalogram and roentgenogram both are nouns.

Word	Noun	Adjective	Verb	Adverb
encephalogram	Yes	No	No	No
roentgenogram	Yes	No	No	No

As nouns, roentgenogram is a hypernym of encephalogram; that is, roentgenogram is a word with a broader meaning than encephalogram:

encephalogram: an X ray of the brain made by replacing spinal fluid with a gas (usually oxygen) to improve contrast
roentgenogram: a radiogram made by exposing photographic film to X rays; used in medical diagnosis

Other hypernyms of encephalogram include X-ray, X-ray photograph, X-ray picture, X ray.

encephalogram (noun)	roentgenogram (noun)
an X ray of the brain made by replacing spinal fluid with a gas (usually oxygen) to improve contrast	a radiogram made by exposing photographic film to X rays; used in medical diagnosis
a graphical record of electrical activity of the brain; produced by an electroencephalograph