Biomedical Engineering Reference
In-Depth Information
Figure 3.2: Registration algorithm. Capital bold words are computer lan-
guage. The outer loop from DO to END gives the multiresolution approach.
The interloop from REPEAT to UNTIL is for restarting registration. Regis-
tration results and number restarts are used to store temporary values in
the program. See text for details. * CC is used at lower resolutions,
1
/
4
or
/
2
number of voxels. ** MI is used only at high resolution, full number of
voxels.
1
perform registration from low to high resolution. At low resolution, we resam-
ple both images at 1/4 or 1/2 number of voxels along each linear dimension,
respectively. Iterative optimization of the similarity is used to vary the six rigid
body transformation parameters (three translations and three angles). We use
the correlation coefficient at the two lower resolutions because of two superior-
ities: (a) it gives fewer local maximums and (b) it can be calculated faster than
MI. We use MI at full resolution because the peaked similarity function gives a
more precise solution than CC.
We create a method to avoid local minima by restarting the registration with
randomly perturbed parameters obtained from a uniform distribution about the
