Biomedical Engineering Reference
In-Depth Information
as bifurcations of blood vessels or the center of the orbits of the eyes), or sur-
face curvature features that are well defined in 3D. Several methods have
been reported to register clinical images using corresponding anatomical
landmarks that have been identified interactively by a skilled user.
9-11
Assuming all markers are identified with the same accuracy, registration
error as measured by TRE can be reduced by increasing the number of fidu-
cial markers. If the error in landmark identification or FLE is randomly dis-
tributed about the true landmark position, the TRE reduces as the square root
of the number of points identified, for a given spatial distribution of points.
TRE values of about 2 mm at the center rising to about 4 mm at the periphery
are to be expected when registering MR and PET images of the head using 12
anatomical landmarks well distributed over the image volume. For register-
ing MR and CT images, including the skull base, typical misregistration
errors (TRE values) will be about 1 mm at the center, rising to about 2 mm at
the periphery for 12 to 16 landmarks.
11
Finding these landmarks automati-
cally and reliably is difficult and remains a research issue.
Figure 2.5 shows an example of aligned and combined CT and MR volumes
of a patient with a large acoustic neuroma extending into the internal auditory
meatus. These images are useful for planning skull base surgery.
10
Figure 2.6
depicts an aligned MR and PET image of the head showing that a suspicious
bright region seen on contrast-enhanced MR does not correspond to a region
FIGURE 2.5
Slice (bottom) through a 3D volume formed by aligning and combining CT (top left) and MR
(top right) volumes. CT intensity is displayed when this corresponds to bone otherwise the
MR intensity is shown. This type of display has been useful in planning skull base surgery.
10
