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:As previously reported [15, 16, 22] and according to recent findings [17, 29] regarding scanning influences on neural baseline conditions, PET investigations might be useful in the same way as a functional MRI (fMRI) study in which the temporal resolution is in the range of minutes instead of seconds [22, 30].
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