ABSTRACT
This paper proposes a state of the art
manufacturing procedure for customized artificial limbs and joints. Amazed??
Read on.
The technique described in this paper
tries to utilize the advanced Computer Aided Design (CAD) / Finite Element
Analysis (FEA) to detect and understand the stress points in the knee, hip and
the shoulder joints, and aid in the manufacture of artifical joints and limbs.
This system takes input and CT scan,
which is then fed into CAD by means of an external reference. What is there now
in the CAD is a two dimensional representation of the joint. The next step is
to feed the data into a Solid Modelling Software so that a three dimensional
representation of the joint is obtained. Once a true representation is obtained
a Computer Aided Engineering software which uses techniques like finite element
analysis gives the detailed views of the strengths and weaknesses of the
different parts. The output of this would be useful in applications like
surgery, manufacture of personlized artificial limbs etc. Rapid prototyping is
the next phase that would be adobted in the manufacture of the desired joint.
Voila !!
INTRODUCTION
The scientific research in the field of structural
optimization has increased very substantially during the last decades, and
considerable progress has been made. This development is due to the progress in
reliable general analysis tools like the finite element method, methods of
design sensitivity analysis, and methods of mathematical programming, and has
been strongly boosted by the exponentially increasing speed and capacity of
digital computers. This is practically
made possible by using Computer Aided Design and Analysis, which accounts for
completeness and accuracy. The above applications can be utilized in
determining the structural stress points in the human body Three-dimensional
models are necessary for the realistic finite element analysis of joints and
implants. Interfacing directly medical data to a FEA and CAD environment can
improve the biomechanical analysis of joints and the design process of orthopedic
implants providing very useful geometric information on different tissues. A
direct interface between medical scanners and engineering software was used
which allowed the utilization of CT an MRI scanner data for the generation of
solid 3D models of joint structures. A system of commercially available
software titles was utilized to interface data from the individual scanner
format to a format usable in FEA and CAD software.
The cases of the knee, hip and shoulder joint are examined.
It has been possible to reconstruct the different tissue types of the joints
and represent them by different volumetric entities within a FEA/CAD
environment. In such a way it has been possible to represent geometrically the
imaged structures in an accurate way and to assign different material
properties limiting assumptions. Exporting medical imaging data to a CAD
readable format has also allowed the rapid prototyping of the joint structures
providing hard copies for the verification and fitting test of new implant
designs.
A practical
and accurate system was identified for the interface of medical imaging data to
an engineering environment, providing an automatic generation of joint computer
models that can be used in FEA/CAD and Rapid Prototyping. Implant designs can
be compared with real patient data. Implants and joint tissues can be combined,
viewed, manipulated, modeled and analyzed within a single environment. The
method is suggested as a better analysis tool for joints and as an improved
design process for joint replacements.
Bio-medical methods
Bio Medical
Modeling embraces various techniques that allow the development of virtual or
physical models of anatomical structures based on the information present in
medical images (CT, MRI...). Until now, interfacing medical image data to
external systems has been a particularly demanding task, requiring specific
hardware, software and expertise. Medical scanners have been 'closed systems'
(medical scanner and workstation form a single integrated system) that offer
limited or no external access to their data. An interface system must combine:
segmentation, visualization and manipulation of medical imaging data in an
efficient, practical and accurate way for use in a research and clinical
environment.
The
general Bio Medical Modeling method is presented below:
Step
1: Image Format Recognition and Interface
Step
2: Image Processing and Tissue Identification
Step
3: Three Dimensional Reconstruction
Step
4: Anatomical Modeling:
Computer
Aided Design Computer
Simulation – Finite Element analysis
Physical
Reconstruction – Medical Prototyping
Step 1: Image Format Recognition and Interface
A wide range of
formats can be recognized and utilized (Philips, GE, Hitachi
Step 2: IMAGE PROCESSING AND TISSUE IDENTIFICATION
Wide ranges of tools
give us the power to enhance the image data generated by the CT or MRI scanner.
It is possible to enhance contrast; perform a fully automatic tissue selection;
draw or erase tissues on each image as well as localize tissue selection;
display the original scanned data along with two reconstructed views in the
orthogonal planes and move images in each view in real time.
Step 3: THREE DIMENSIONAL RECONSTRUCTION
Three-dimensional
computer models of selected anatomical structures can be automatically
developed within minutes utilizing data of various scanners (GE, Siemens,
Phillips, etc.). The reconstruction can be viewed from any angle. Real time
rotation along with the ability to apply transparency to the model is
available. Advanced visualization methods also allow the combination of the model
or the images with Computer Aided Design (CAD) objects. For example, an implant
design can be visualized in two-dimensional cross sections along with the
original CT/MRI data to verify interaction with the relevant tissue and correct
positioning.
Step 4: ANATOMICAL MODELING
CAD
Modeling of Anatomical Structures
Computer Aided Design
(CAD) is nowadays used for the design of all kind of medical devices.
Introducing geometrical information of anatomical structures within a CAD
environment facilitates the design of any standard or custom made implants,
prostheses or relevant components. Any such data had, until now, to be manually
entered into the CAD environment resulting in complicated, time-consuming and
impractical procedures that often resulted in computer files of enormous size
requiring extremely powerful computer systems. Such methods were inefficient
for use within a hospital environment or small research centers.
Non-compatibility of hardware and software components has also been a very
important issue. Image data once visualized segmented and three dimensionally
reconstructed can be imported into a CAD environment. Solid surfaces, usable by
common CAD software (STL, IGES etc.), can be generated over the 3D
reconstruction. A bridge technology between scanner data and CAD systems is
applied. Reference objects can be generated within the original imaging data
and complex surfaces of organs can be combined with medical devices in a CAD
environment. CAD objects, such as implants, can be imported within the medical
data, facilitating their design. The CAD environment serves also as a tool for
further modeling of the anatomical structures. Using such an interface,
image-based medical design becomes a reality.
Computer
Simulation - Finite Element Analysis (FEA)
Finite Element
Analysis (FEA) is widely used for the investigation of various mechanical
components. In the medical field, FEA is used for the prediction of stress
distribution around and within implants and the results are used in the design
of medical devices. Until recently, most models have been two-dimensional and
have introduced approximations regarding the presence of important tissues and
their properties. In addition, finite element model development has been manual
and time-consuming, producing large computer files. Medical imaging data could
not be easily utilized, until now, to solve three-dimensional complex models.
Physical
Reconstruction – Medical Prototyping (MRP)
Medical Rapid
Prototyping (MRP) is the latest technique that allows us to build complex
physical models of a patient's anatomy directly from images of a hospital
scanner. During the last few years, the combination of medical image processing
and rapid prototyping has proved to be a very important development, still to
be applied on a large scale in medicine, and especially, surgery.
Medical models are now
used by different skill centers all around the world for a large variety of
applications: 3D visualization of specific anatomy, diagnosis and communication
of complex pathologies, pre-operative planning of surgical interventions,
custom-made implant design, production of customized medical devices, surgical
templates, teaching aids.
A direct interface
between the three-dimensional reconstruction and rapid prototyping allows the
development of physical, real 3D, models of any anatomical structures. Such
models are used for purposes of: visualization & communication, surgery
rehearsal and custom implant preparation. Various RP systems can be used, but
in each case, the technique is similar:
- The RP system accepts data in a format that accurately
describes the surface of the component.
- The RP system software "slices" the model
data into very thin sections.
- The RP system then builds the model
slice upon slice.
Almost any complex
shape can be modeled. The accuracy of RP models is usually better than 0.1 mm,
which is suitable for most cases. Models can be delivered within 10 working
days of receiving valid image data.
Conclusion
As
per the data framed from this interface it is possible to achieve an artificial
joint i.e. replacing the worn out one accurately by the computer aided design
and finite element analysis techniques with the output obtained by a technique
which has shown an accuracy of 0.1mm which is rapid prototyping. This is an
amazing fact because if a part is worn out in a convectional machine with the
help of design of experiments it is replaced but if in a human machine if the
part gets worn out it leads to miseries and unhappiness. By the application of
these techniques the worn out part such as hip, knee & shoulder joints in
the human machine can be replaced. This has been successfully implemented at United Kingdom India
References
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Concept-Taken From Sussex University Centre , U.K.
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