Table 1.

Models for Diffusion Tensor Estimation

Model (m)	Tensor estimation	Linear noise regressors (number)	Nonlinear regressors (number)	Total number of regressors p(m)
(i)	Standard tensor model	n.a.	n.a.	6
(ii)	Extended tensor model	Cardiac phase (4)	None	10
(iii)	Extended tensor model	Cardiac and respiratory phase (8)	None	14
(iv)	Extended tensor model	None	Cardiac phase (2)	8
(v)	Extended tensor model	Respiratory phase (4)	Cardiac phase (2)	12
(vi)	Robust fitting	n.a.	n.a.	6

The different models that were used to estimate the diffusion tensor are depicted. The total number of regressors p^(m) consists of the six tensor regressors and m noise regressors. Note that although the total number of regressors is six for the robust fitting model the effective degrees of freedom can be reduced by more than 6 because of the down-weighting of outliers.