To achieve common anatomical coordinates across subjects, a population-average FA template (Sullivan et al. 2010a) was constructed from the FA data of 120 control subjects (20–81 years old) with group-wise affine registration (Learned-Miller 2006) followed by iterative nonrigid averaging (Rohlfing and Maurer 2003). Each subject’s FA data set was registered to the population FA template with a nine-parameter affine transformation followed by nonrigid alignment using a multi-level, third-order B-spline, with 5-mm final control point spacing (Rohlfing and Maurer 2003; Rueckert et al. 1999).
