Page 83 - Computational Modeling in Biomedical Engineering and Medical Physics

CHAPTER 3

Computational domains

3.1 Physical domains generated using computer-aided design
techniques

The use of computational power in the generation, editing, or optimization of a
design is called computer-aided design (CAD) (Narayan, 2008). CAD is frequently
used in the industrial design and testing phases. Engineers are using it for creating
complex multipart models and to study their behavior under certain conditions:
mechanical or thermal stress analysis, repeated cycle movements, wear, deflections, etc.
Regardless of its applications, it is difficult to imagine that a new product release is
possible without the use of CAD in the incipient phases, shortly after the main idea
was sketched by pen on paper.
CAD is now also used in the medical and clinical fields, from the prosthesis drawings
and patient-specific geometry optimization to virtual platforms that help the medical staff
to train and improve different surgical techniques with low costs and great benefits. In
the following sections, a set of CAD-generated body parts will be presented.

A CAD construct for an intervertebral disc
The intervertebral discs can be found in the spinal cord at the junction between two
vertebrae. They play an essential role in the damping of the mechanical stress exerted
upon the spinal cord and allowing the movement of the vertebrae. Two components
can be distinguished in the intervertebral disc structure: the annulus fibrosus, disposed as
concentric lamellas, made of collagen fibers, wrapped around a second part, the nucleus
pulposus (Newell et al., 2017).
Next a CAD-generated model of a human intervertebral disc is presented. This
solid model can be created using simple drawing elements (lines and splines) from any
CAD software environment, for example, Solidworks, Autocad, Inventor, and Catia.
First, the resulted contour of the nucleus (Fig. 3.1A), which represents the anatomical
details (shape and size), was extruded, generating a tridimensional model (Fig. 3.1B).
Then to obtain the surrounding annulus, the nucleus was duplicated and rescaled. The
final model of the intervertebral disc presented in Fig. 3.1B was created. The two
parts, annulus and nucleus are both homogenous in structure. This is not a bad
approach when we look at the nucleus, but in some cases, it could become a draw-
back to consider the annulus as a whole. For example, in mechanical stress analysis, a
more accurate description of the annulus internal structure as concentric lamellas made

Computational Modeling in Biomedical Engineering and Medical Physics r 2021 Elsevier Inc.
DOI: https://doi.org/10.1016/B978-0-12-817897-3.00003-8 All rights reserved. 71