Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…SNRe for uniform stretching of the postcompression A-lines (performed to undo the effects of mechanical compression on the signal itself and, hence, improve the correlation between the pre- and postcompression A-lines) have been developed in elastography (Céspedes 1993; Varghese and Ophir 1997b).
Category: