Medical images (1-4)
I believe the answer is:
x-rays
'medical images' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for x-rays that I've seen before include "Electromagnetic waves, for medical diagnoses, say" , "Diagnostic radiation" , "Photos or exams made with kind of radiation" , "Hospital photos" , "'Electromagnetic waves, for medical diagnosis say (1-4)'" .)