Biomedical Engineering Reference
In-Depth Information
Figure 8.15: Final 3D results of the registration on real data. Top: difference
before registration. Middle: difference after registration. Bottom: adaptive par-
tition at grid level 3. The difference volumes must be interpreted carefully, since
we get the superposition of two errors: the first one is the registration error
which comes from the anatomical variability that we could not apprehend. The
second error is due to the difference of acquisition of the two volumes, which
makes the two original histograms of the two volumes different.
The 3D deformation field is presented in Fig. 8.17. The vector field is sub-
sampled in order to be easier to look at, and we also show the three components
of the field on the sagittal view. Although discontinuities are visible, the general
spatial coherence of the final deformation field is visible, due to the regulariza-
tion. The field also confirms that there is no “block-effect” in the registration
process.
The computation takes about 1 : 30 hour on an Ultra Sparc 30 (300 MHz).
The volumes are 256
×
256
×
200. We use three levels of resolution (
k
=
0
,
1
,
2)
because the displacement amplitude may reach 30 voxels, and at each resolution
level we perform the registration from grid level 4 until grid level 0.
