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:False negatives can occur if the object is small or if a hypointense structure or signal void is mistaken for a tendon, dense collagenous structure, or air.(15) Compared with both ultrasound and CT, MRI is the most limited in spatial resolution.
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