Biomedical Engineering Reference
In-Depth Information
Materials and Methods
A quantitative assessment of femur stresses under physiologic conditions is
essential for the understanding of failure mechanisms and providing guidance for
the design and operation of femur replacement. Three-dimensional FE models are
created using CT images in materialized interactive medical image control systems
(MIMICS) and then its surface mesh is created in MIMICS after which this surface
mesh is converted into volumetric mesh in ABAQUS and assigned material
properties to these models in MIMICS, and finally transferred into ANSYS for
FEA
under
physiological
loading
conditions
where
total
deformation,
stress
distribution, and fatigue tools are obtained throughout the femur.
Image Acquisition
The CT data of total femur of normal individual male patients of 17, 32, and
40 years are collected. This geometrical data of real proximal human femur bone
is in the form of digital imaging and communications in medicine (DICOM) file.
The CT scanning of patient is obtained using GE Ultrafast High Resolution
Multislice CT Scanner (16 Slice) containing a total number of 909, 667, and 1,714
images, respectively, pixel size of 0.7031, 0.8867, and 0.9766 mm, respectively,
slice thickness of 0.4 mm, and resolution of 512 9 512. DICOM file is a standard
for handling, storing, printing, and transmitting information in medical imaging
and contains binary data elements. In MIMICS, distinctive CT images are a pixel
map of the linear X-ray attenuation coefficient of tissue. The pixel values are
scaled so that the linear X-ray attenuation coefficient of air equals -1,024 and that
of water equals 0. This scale is called the Hounsfield scale after Godfrey
Hounsfield, one of the pioneers in CT. Using this scale, fat is around -110, muscle
is around 40, trabecular bone is in the range of 100-300, and cortical bone extends
above trabecular bone to about 2,000. The pixel values are shown graphically by a
set of gray levels that vary linearly from black to white. MIMICS displays CT
images using up to 256 gray levels of the display setting.
Geometric Modeling/Image Segmentation
For this comparative study, we have created three models of right femur of male
human patients: Model 1 of a 17-year-old male, Model 2 of a 32-year-old male, and
Model 3 of a 40-year-old male. MIMICS is an interactive tool for the visualization
and segmentation of CT images as well as MRI images and 3D rendering of objects.
Therefore, in the medical field MIMICS is used for diagnostic, operation planning,
or rehearsal purposes. Figure 1 shows the image of a normal individual total femur
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