FIG. 4.

Validation step 2 (DWI to T₂ registration). (a) As an intensity-based measure, the normalized cross correlation $\mathrm{NCC}(T_2^{\prime },D_0^{\prime T})$ between the absolute gradient images $T_2^{\prime }$ and the transformation of $D_0^{\prime }$, $D_0^{\prime T}$ was computed to estimate how well the image edges of T₂ align with those in $D_0^T$. (b) As a measure of real anatomical motion, we computed the target registration error $\mathrm{TRE}(T_2,D_0^T)$ over a set of landmarks that were manually selected in T₂ and in D₀ and located in $D_0^T$ based on the estimated motion fields.