positron emission tomography vs PET

positron emission tomography and PET both are nouns.

Word	Noun	Adjective	Verb	Adverb
positron emission tomography	Yes	No	No	No
PET	Yes	No	No	No

As nouns, positron emission tomography and PET are synonyms defined as:

positron emission tomography and PET: using a computerized radiographic technique to examine the metabolic activity in various tissues (especially in the brain)

positron emission tomography (noun)	PET (noun)
using a computerized radiographic technique to examine the metabolic activity in various tissues (especially in the brain)	using a computerized radiographic technique to examine the metabolic activity in various tissues (especially in the brain)