Biomedical Engineering Reference
In-Depth Information
FIGURE 2.8
This illustrates in 2D how a contour-based method of alignment can produce multiple
solutions if the contour exhibits axes of symmetry, in this case cranio-caudal tilt. Both
alignments of the thick dotted line and thin continuous line will produce very similar mean
distances between the two contours. The same arguments apply to surfaces in 3D.
FIGURE 2.9
18
An example of three orthogonal slices through a 3D MR volume overlaid with the PET
FDG
volume. The volume is grossly misregistered, yet the outline of the brain is surprisingly
well aligned. (C. Studholme, Ph.D. Thesis, University of London, 1997.)
2.4.2.2
Distance Transforms
Surface matching was made more computationally efficient by precomput-
ing the distance from every point in space to one of the surfaces to be regis-
tered. This is called a distance transform and makes the computation at each
iteration much faster.
