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:Although these twomethods described above were originally proposed for single-shell data, they can be generalized for multi-shell data using two different approaches:
 ‚Ä¢ First fit diffusion models, such as DTI (Basser et al., 1994) or Spherical Polar Fourier Imaging (Assemlal et al., 2009; Cheng et al., 2010b), to high-anisotropy diffusion signal E(q) in R3.
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