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:[24,25] However, planar I-131 imaging has traditionally suffered from low resolution, and a paucity of anatomic information along with a long list of physiologic variants makes image interpretation challenging.[26] Therefore, it is assumed that the reason why functioning ETT in TGDR has been underestimated in patients with DTC is mainly due to the poor image quality of an I‐131 scan.
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