Biomedical Engineering Reference
In-Depth Information
Figure 6.6-6 Visualization of the functional correlation of vascular volume and vascular permeability in tumor mass obtained in vivo
using MR microscopy (125-micron) technique. 3D volume visualization using color space registration shows that there is little
overlap between vascular volume (green) and vascular permeability (red), confirming previous observations. (Images courtesy of
M. Solaiyappan, Zaver Bhujwalla, Dmitri Artemov.)
structures from the volume data. In cases where the an-
atomical structures of interest cannot be extracted with
a unique threshold, surface rendering may be difficult to
use. Volume rendering blends the data over a range
suitably weighted by a transfer function. However, in its
original form, it does not take into account the spatial
connectivity between various structures in the data, thus
making it sometimes difficult to select a particular
structure of interest. Shell rendering combines spatial
connectivity information addressed by surface rendering
with voxel level blending of data provided by volume
rendering. Thus, if surface rendering is considered as
a ''hard-shell'' based on its specific threshold values, the
shell rendering can be thought of as a ''soft-shell'' based
on its fuzzy threshold.
Volume encoding (octrees)
During the development of various rendering techniques,
encoding of volume data emerged as a research topic.
When they became first available, sets of volume data were
relatively large in comparison to the limited disk storage
capacity of the time. Representation and processing of
volume data required a great deal of memory and com-
puting power. Octree encoding of the volume took ad-
vantage of clusters of data points that could be grouped.
Appropriate grouping of these data points could result in
substantial reduction in storage and yield high speed in
volume rendering. A cluster of cells partitioned by octree
encoding can be processed in one step instead of the
several steps that may otherwise be required.
A more versatile approach would be a 3D wavelet-
based approach, which could help maintain multilevel
resolution of the volume. It could provide image com-
pression and improve the speed of rendering during in-
teraction by using low resolution.
Texture mapping for 3D images
The concept of 2D texture mapping was extended to 3D
images. However, unlike 2D texture mapping, the 3D
texture mapping technique does not produce a 3D ren-
dered image directly from a texture map. It only provides
a fundamental but powerful capability called multiplanar
Figure 6.6-7 Visualization of breathing lung: navigational
visualization (virtual bronchoscopy) using segmented bronchial
tree. (Images courtesy of M. Solaiyappan, S. A. Wood,
E. Zerhouni, W. Mitzner.)
