MATERIALS
The pelvic organs, concentrating on the internal reproductive
tract of the Visible Human Project-Female (VHP-F) and a unique, cryo-preserved human
female pelvis cadaver of a 30 year old woman, the Stanford
Visible Human-Female (SVH-F) are
being extracted for developing 3D models. Among the pelvic
organs of primary interest to gynecologic surgeons, the uterus,
fallopian tubes and ovaries are compared in this initial study.
METHOD
A rectangular volume of data, enclosing the reproductive organs
of interest, was selected from each of the two datasets. From
the VHP-F, this volume comprised 155 slices, 450 pixels wide x
500 pixels high (pixel size ~0.343mm, slice separation 0.33mm).
From the SVH-F, this volume comprised 30 slices, 475 pixels wide
x 525 pixels high (pixel size ~0.25 mm, slice separation 1.5mm).
Each pixel in the volume was converted from a 24-bit RGB color to
an 8-bit grey value using the formula:
I = 0.2989 * R + 0.5870 * G + 0.1140 * B
where, R, G and B are the pixel intensity in the red, green, and
blue channels respectively, and I is the intensity of the
resulting grey scale pixel.
The grey scale volume was processed through volume rendering
software, X3D, provided by CEMAX-ICON, Inc., running on a Sun
Ultra 1. Cut planes were defined so as to eliminate overlying
structures such as bowel, and to make visible the ovaries and the
uterus. The rendering software allowed us to define a range of
grey scale intensities that highlighted the desired organs,
separating them from the surrounding fat and other tissues.
|
Prior to conversion of slice data into three-dimensional surface
models, it was necessary for a content expert (WLH) to preprocess
every slice and mask out all except the relevant structures.
This manual step was necessary because efforts at automated
segmentation would always cause unwanted nearby structures of
similar intensity to be included along with the desired organ.
Three dimensional surface models were constructed using the
Visualization Toolkit (vtk) software, available from General
Electric Comapny, and the Tcl interpretive language, operating on
a SGI Indigo 2 workstation. For generating the models, marching
cubes and various filtering algorithms were applied to transform
the slice data into outlines of objects, and then into a
triangulated surface. Further refinement was accomplished by
converting the models (written in STL format) into Inventor
format and applying VisModel CAD modeling software from
Engineering Animation, Inc.
RESULTS
Images, presented as a movie for each dataset (see links in the
Materials section), represent the comparable slices. Differences
are clearly visible in the shape, size, and position of the
reproductive organs. We measured the antero-posterior dimension
of the uterus and ovary. In the SVH-F, a woman of reproductive
age, the uterus measures 4.6cm and the ovaries are 1.8cm. In the
VHP-F, a post-menopausal woman, the uterus is 3.7cm and the right
ovary is 1.0cm. Another movie presents a rendered view of a 3D
surface model of the ovaries and uterus (SVH-F-3D) derived using the methods above.
CONCLUSION
These procedures permit development of authentic, integrated, 3D
surface and solid organ models that can form the fundamental
virtual anatomic regions of surgical interest (AROSI) essential
for simulations of videoendoscopic surgery.
|