Real-time simulation of mechanical properties on virtual reality: A methodology to improve geometric segmentation, mathematical modeling and characterization of soft tissues
Export citation
Resumen
In this research project, it is presented a methodology to achieve the development
of technological tools and material knowledge that support the real-time simulation
of soft tissues for virtual reality. Particularly, this work is focused on two main areas
that were identified in previous work as opportunities for improvement: Geometrical
and Material Modeling. These areas are key to develop not only medical training
processes, but also other research projects that involve soft tissue and composite
materials characterization, design and development of biomedical devices, and
augmented reality tools, among others.
As one of the goals, it is proposed to create virtual tools that allow the interaction,
processing, and segmentation of medical images in a semi-automatic way. This was
detected by questioning how to increase the applicability of the simulation framework
to other anatomical geometries and simplify the creation of new and customized
medical cases based on their own set of images.
The solution proposed is to provide the user with access to an interactive learning
experience based on 3D rendering of medical images. This will not only allow
visualization of medical cases but also have a relatively quick and simple process to
get anatomically realistic 3D geometries for simulation, design of new products or
3D printing of models. In this path, it was developed the module VISUALIX, which is
able to provide said interaction, and the results are presented in chapter 4. Also, a
proposal for fractal structure analysis was done using microtomography images,
creating FractalCells module with the implemented tools.
For material modeling and characterization of soft tissue, a new hybrid formulation
is proposed by questioning how a simple technique like Spring-Mass Model (SMM)
can describe the soft tissue mechanical properties, if it is based on linear elasticity
theory and therefore it can only be used to predict small deformations (<10%).
The solution proposed is based on the application of a constitutive model able to
describe the mechanical behavior of soft tissue, as well as other composite
materials. For this purpose, it is created a hybrid construction of a Strain Energy
Density Function (SEDF) used to find an energy equivalence with a variable stiffness
SMM. This formulation was named Equivalent Energy Spring Model (EESM) and is
Abstract ii
presented in chapter 5. It is able to characterize soft tissue properties of non-linearity,
anisotropy, and Mullin’s effect, to predict its response at large deformation (>10%).
Finally, and in order to validate the proposed model, an experimental phase was
defined to perform uniaxial and biaxial cyclical tensile tests with porcine tissue
samples in order to have experimental data for material characterization using
EESM. This experimental phase is described in chapter 6. The results for the
characterization of porcine liver and abdominal wall tissues, as well as the
predictions of the EESM formulation are presented in chapter 7, including an
evaluation of its accuracy and its capacity to perform in real-time.