J. Ruiz-Alzola, C.F. Westin, S.K. Warfield, C. Alberola, S. Maier, and R. Kikinis. Nonrigid registration of 3D tensor medical data. Medical Image Analysis, 6(2):143-161, June 2002. (pdf) (bibtex: RuizAlzola-2002-NR3).