The document discusses the creation and comparison of 3D-printed and finite element analysis (FEA) models of a porcine lumbar vertebra created using various open source software packages. Key findings include: - 3D-printed models created with 3D-Slicer and MIMICS software were measured and found to be geometrically similar, with minor differences attributed to smoothing and measurement errors. - FEA models were significantly stiffer than actual test results and published data. The model using equations from Morgan et al. was closest but still stiffer. - Customizing material properties in the FEA model improved results, but equations require further validation. - The study demonstrated a process for creating

1. The 3D-printed models created using 3D-Slicer and the ‘MIMICS’
software package were measured and compared using a Vernier
callipers to measure the vertebras key parameters.
The 3D-printed model created using 3D-Slicer, was geometrical similar
to the model created by Mr. Colin Bright using the Mimics software
package. The differences observed between the two models may be
attributed to the errors associated with smoothing the model and
with measuring such a complex shape using a Vernier callipers.
All of the FEA models created were very stiff in comparison to the
actual and published works. The model created using the equation by
Elise F. Morgan et al. [5] displayed a stiffness of 87.72 kN/mm
compared to the stiffness of 6.913 kN/mm recorded in the actual test.
The model containing only two material properties performed closest
to the actual results, displaying a stiffness of 19.33kN/mm.
This project has demonstrated a method of creating patient specific
FEA models using freely available software. However the equations
used require further research in order to ensure agreement between
the actual and FEA results.
[1] L.Feng & I.Jasiuk, ‘Multi-scale Characterization of Swine
Femoral Cortical Bone’, 2011
[2] S.C. Lee et al., ‘Tibial Ultrasound Velocity Measured
InSitu Predicts the Material Properties of Tibial Cortical
Bone’, 1997
[3] Lin et al., ‘Distribution and regional strength of
trabecular bone in the porcine lumbar spine’, 1997
[4] Kopperdahl & Keaveny, ‘Yield strain behaviour of
trabecular bone’, 1998
[5] Elise F. Morgan et al., ‘Trabecular bone modulus–density
relationships depend on anatomic site’ 2003
[6] Ruth K. Wilcox, ‘The influence of material property and
morphological parameters on specimen-specific finite
element models of porcine vertebral bodies’ 2007
Student Name: Mr. Christopher Mc Clelland
Supervisor’s Name: Mr. Stephen Tiernan
4th year Project, ITT Dublin, Tallaght, Dublin 24
I would like to take this opportunity to thank my supervisor Mr.
Stephen Tiernan, and the post graduate students, Mr. Colin Bright and
Mr. Philip Purcell for their guidance and support throughout the
process of this project.
• Create an STL file of the L4 vertebra from a CT scan of a porcine
lumbar spine.
• 3D-Print a solid model of the segmented vertebra and compare
with models created using industry leading software.
• Create a meshed model of the vertebra with two material
properties (hard cortical shell & a soft cancellous core) based on
the findings of the literature review.
• Create a meshed model of the vertebra with specimen specific
material properties using image based techniques.
• Conduct a FE analysis on the models created, using the ‘ANSYS’
software package.
• Compare the results of the FEA with the actual tests conducted by
the post-graduate students and with other published works.
Dimension
3D-Slicer Model
(mm)
Mimics Mode
(mm)
% Diff.
End Plate Width (upper) 36.20 37.42 3.26%
End Plate Width (lower) 39.37 40.59 3.01%
End Plate Depth (upper) 21.64 23.23 6.87%
End Plate Depth (lower) 19.95 20.87 4.38%
Pedicle Height 25.42 23.24 -9.38%
Pedicle Width 11.82 11.76 -0.51%
The results of the simulated compression tests carried out on the FEA
models using the ANSYS software package, were brought into
‘Microsoft Excel’ in order to perform comparative analysis with the
actual and published results.
0
2000
4000
6000
8000
10000
12000
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Load(N)
Displacement (mm)
Load vs Displacement (Results of FE Tests)
FE TEST (Custom Settings 1 B=1100 C=2) FE TEST (Elise F. Morgan Settings)
FE TEST (IA-FEMesh Settings) FE TEST (User Defined Settings)
Mr. Colin Bright (Real World Test Data) FE TEST (Wilcox Max Stiffness)
Table 1: Results of Comparative Analysis of 3D-Slicer & MIMICS Models
This flowchart illustrates the steps taken using these software packages.
COMPRESSION
TESTING
SEGMENT CT SCAN
CREATE LABEL MAP
GENERATE MODEL
3D-PRINTED MODEL
IMPORT IMAGE &
SURFACE
CREATE BUILDING
BLOCKS
ASSIGN MESH SEEDS
CREATE MESH
ASSIGN MATERIAL
PROPERTIES
IMPORT MESHED
MODEL (RETAINING
MATERIAL
PROPERTIES)
LOAD & SUPPORT
MODEL
RUN COMPRESSION
TESTS & RECORD
RESULTS
Figure 2: Graph of Results for Comparative Analysis
Software Packages Chosen: 3D-Slicer, IA-FEMesh & ANSYS.
3D-Slicer
3D-Slicer began as a master’s thesis project in 1998 and has operated
on a community based platform, whereby it is developed constantly
by developers based on user feedback. Its development has been
funded by the ‘NIH’ and several other federal sources. This project
utilised 3D-Slicer to process the CT scan of the porcine lumbar spine,
segmenting the L4 vertebra, creating an STL file of said vertebra and
3D-Printing a solid model of the vertebra.
IA-FEMesh
IA-FEMesh began as an ambitious project by ‘The Musculoskeletal
Imaging, Modeling, and Experimentation’ (MIMX) Program at The
University of Iowa. It was created in an effort to facilitate anatomic FE
model development. This project utilised IA-FEMesh to create a
number of finite element meshed models of the segmented L4
vertebra. The meshed models were created using two different
techniques. User defined properties were set based on the findings of
studies conducted by L.Feng & I.Jasiuk[1], S.C. Lee et al.[2], Lin et al.[3]
and Kopperdahl & Keaveny[4]. The image based properties use power
law equations to relate material properties of the bone, to the grey
scale values of the CT scan image. Image based models were created
using the default settings in IA-FEMesh, the findings of a study by Elise
F. Morgan et al. [5] and also using a custom setting defined by this
research project.
ANSYS
The models created where then imported into the ‘ANSYS’ software
package, where they underwent simulated compression tests. The
results of these FEA tests was then compared to the actual test results
gathered by Mr. Colin Bright and to the published FE test results of
Ruth Wilcox[6].
Spinal research and testing pose many difficulties. Especially with
regards to the limitations and difficulties associated with obtaining
human specimens. However as new technologies emerge the number
and variety of surgical techniques for the spine continues to grow. “In-
Silico analysis”, a computerised method of medical investigation, has
become more widespread in its use in recent times. In particular there
has been an increase in the use of finite element analysis (FEA) in
spinal research. The benefits of using in-silico analysis in medical
research are numerous.
• It offers a non invasive approach which allows for multiple tests to
be carried out without any effect on the patient
• This in turn allows for the selection of the most appropriate
treatments & surgical techniques for a specific patient.
However the process of creating an FEA mesh is complex and
laborious because the creation of patient specific models including
material properties is difficult. As well as that, clinically approved
medical imaging software is still very expensive.
As a result it is vitally important to investigate various methods of
creating a FEA mesh model from medical images.
The purpose of this project is to investigate the use and validity of
freely available, open source software packages for medical image
processing. Including the development of solid and FEA models
directly from these software packages.