Biomedical Engineering Reference
In-Depth Information
an effective refining process. Therefore, 3-D scanning technology and computed
tomographic (CT) technology could be introduced.
In 3-D scanning technology (3-D digital technology), stereoscopic material is
taken as a description object and a 3-D special axis is exported, including every sam-
pling point of the object's surface and a color model along with color information.
Hundreds and millions of measuring data could be obtained by noncontact stereo
scanning equipment according to the property of the stereo scanning equipment,
scanning parameters, and size of object measured. The large amount of stereo data
is called the point cloud. Each set of stereo data includes not only stereo axis
information but also color information. With stereo scanning, the method of reverse
engineering could be used. While designing and manufacturing industrial products,
reverse engineering could describe specially as measuring process for accessory
original shape or sample model without designing drawing or sample model to
reconstruct the designing drawing or CAD (computer-aided drawing) model.
There is contact and noncontact 3-D scanning technology according to the
manner of collection. For contact 3-D scanning technology, a 3-D axis is obtained
by contacting an object directly with a measuring machine probe. The precision
of contact 3-D scanning technology is high, but efficiency is low. It is not usually
used in reverse engineering. Noncontact scanning technology making use of optics
emerged in the 1990s in euramerican countries. At present, structural light 3-D
scanning technology is based on a white light lamp house. This technology was
introduced into the industrial scanning measurement area because of its high
precision, high speed, large scanning range, and so on.
At present, 3-D scanning technology is mainly applied in the mold-making area,
including the molding of teeth, body, accessories, costume, spaceflight, and so on.
The distance used between points could reach 10-30
m. It would be helpful to
import this technology for stereomorphology research of cellulose materials in the
primary refining process.
Computed tomographic technology scans a thickness layer of the human body
with X-rays. The X-rays penetrate a thickness layer and could be accepted by a
probe. Then, it would be converted to visible light, which is then converted to
an electrical signal by photoelectric conversion. Finally, the electrical signal is
transformed into a figure by an analog digital converter and sent to a computer
for disposal. To form an image, the chosen layer is divided into a cuboid of the
same volume, which is called a voxel. The scanning information is calculated to
obtain the X-ray attenuation constant or absorption constant of each voxel. Then,
the constant is arranged as a digital matrix that can be stored in a disk or compact
disk. Digitals in the matrix are converted into small squares with different colors of
gray from black to white, which is a pixel. Pixels are arranged as a matrix to form
the CT image. Therefore, the CT image is reconstructing an image. The absorption
constant of each voxel could be calculated with different mathematical methods.
The CT image is constructed by gray voxels as they range from black to white and
are arranged as a matrix. A pixel reflects a related X-ray absorption constant. Images
are obtained with different CT equipment are different in pixel size and number.
The size might be 1.0
1.0 mm, 0.5
0.5 mm, and so on. The number might be
