Biomedical Engineering Reference
In-Depth Information
FIGURE 7.11
Simulated effects of inplane and throughplane shifts on anatomic images: a volume data set
with cubic voxels (0.97 mm on each side) was copied, displaced by one voxel in each of three
orthogonal directions, and then the original data was subtracted from it. A transverse slice
from the volume set (a), the adjacent slice (b), and difference images for left-right (c), postero-
anterior (d), and head-foot (e) displacements are shown. Image (e) results from subtracting
(a) from (b). The differences produced by inplane shifts (c, d) show monophasic and mul-
tiphasic curvilinear changes that can easily be related to the anatomy in (a). Intense signals
with a simple geometry can be seen around the skull and scalp (c, d). The pattern of through-
plane changes (e) is less clearly related to the anatomy shown in (a). The ventricular system
produces curvilinear features as expected from Figures 7.9a[ii]-7.9d[ii]. However, there are
more widespread changes that are patchy or mottled rather than curvilinear. These arise from
throughplane differences between (a) and (b) that have little or no inplane component. Close
inspection is necessary to relate the differences in (e) to the source images (a) and (b).
7.4.2.6
Effects of Change in Shape (without Change in Signal Intensity)
Change in shape involves change in site of at least some of the tissue or fluid,
but it does not necessarily produce a change in size. A change in shape will in
general be accompanied by corresponding shifts elsewhere in the image. Rec-
ognition of these may be straightforward for simple structures and larger
changes, but difficult for complex structures and smaller changes. It requires an
overview of the site and direction of the shifts at different locations in the brain.
7.4.2.7
Effect of Change in Size (without Change in Signal Intensity)
This will also involve change in site and possibly shape. The associated
shifts may be focal or general. The focal changes may be centered on a par-
ticular region while general changes are centered on the structure itself.
