Biomedical Engineering Reference
In-Depth Information
Figure 3.16:
Optimization time and mutual information as a function of VOI
size. The left vertical axis is mutual information, and the right vertical axis is
the total VOI's optimization time. The horizontal axis is the size of the VOI on
a side. In each case, the VOI is centered on the CP, but since even numbers of
voxels are used, the CP is displaced consistently to the upper left-hand corner
by one voxel. With increasing VOI size, time increases linearly with the number
of voxels within the VOI. The peak mutual information value is at a VOI size of
64 on a side. A treatment-diagnosis volume pair is used from S2 with 180 CPs.
values canceled when averaged over the entire image. The standard deviation
of absolute difference is also reduced (Fig. 3.15b).
These quantitative measures match observation from visual inspection. For
example, the third pair of the first group (diagnosis-treatment) in Figs. 15 and
16 correspond with the images in Fig. 3.11. After warping, registration greatly
improved. Another interesting example is the difference images in Figs. 3.13d
and 3.13e that correspond to the last pair of the second group (full-empty blad-
der) in Fig. 3.15. Once again, the statistical measures reflect the great change in
visual quality.
3.3.4.7
Algorithmic Implementation
In rigid body registration, the multiresolution approach and restarting algorithm
were important modifications. First, these two features improved robustness.
