Initially, radiology expert noted acute lesions of the kidneys (5)
I believe the answer is:
renal
'of the kidneys' is the definition.
(I've seen this before)
'initially radiology expert noted acute lesions' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'radiology expert noted acute lesions' is 'RENAL'.
(Other definitions for renal that I've seen before include "connected with organ" , "Learn (anag) - of organs of the body" , "Pertaining to the kidneys" , "Concerning the kidneys" , "Concerned with organ" .)