Finite element analysis and modeling (FEAIFEM) has been used for years as a numerical solution technique for systems of differential equations in the engineering problems of structural analysis and stress analysis.More recently these techniques have been utilized in a biomedical engineering context, for modeling parts of the human body using realistic biomechanical data for the relevant tissues/materials. Furthermore, finite element techniques, used purely as a computer graphics construct, are finding application in physically based modeling and deformable models that incorporate Newtonian mechanics to produce realistic behavior and animations.

Definition of FEA

The Finite Element Method (FEM) is a numerical technique to obtain approximate solutions to a wide variety of engineering problems where the variables are related by means of algebraic, differential and integral equations. Finite elements has become one of the industry standard for solving multi-disciplinary engineering problems that can be described by equations of calculus. Applications cut across several industries by virtue of the applications - solid mechanics (civil, aerospace, automotive, mechanical. biomedical, electronic), fluid mechanics (geo technical, aerospace, electronic, environmental, hydraulics, biomedical, chemical), heat transfer (automotive, aerospace, electronic, chemical), acoustics (automotive, mechanical, aerospace), electromagnetics (electronic, aerospace) and many, many more.

The interface of Medical Imaging, Finite Element Analysis (FEA), Computer Aided Design (CAD) and Rapid Prototyping (RP)

Medical Imaging has been providing important data on various body structures for diagnostic reasons. The possibility of using the provided data, practically and accurately, to obtain geometric information of body structures and generate easily three-dimensional models would be very important. Such models would be very useful for the realistic analysis of structures through FEA techniques and the design of various implants. The development of rapid prototyping models would assist the verification of implant designs but also the visualization and communication of complex pathologies in a hospital environment.

A practical method is identified to interface data from CT and MRI images to FEA, CAD and RP systems. CT and MRI images of various structures, acquired from conventional hospital scanners, provided the input data to the examined interface system of commercially available software packages. The image data was visualized, segmented and three dimensionally reconstructed. Solid surfaces, usable by common CAD systems, were generated. The generated models incorporating tissues of interest were imported in a FEA environment for their finite element modeling. That environment served also as a tool for the further CAD modeling of the imaged structures and their conversion to a format readable by rapid prototyping systems. Rapid prototyping models of the imaged structures were produced using a stereo lithography system.

Such interface was found to provide many advantages. The time taken for the development of a FEA model and the computer resources necessary for the analysis of complicated 3D models was greatly reduced. The various tissue types were accurately represented geometrically, allowing registration of the different material properties. The analysis assumptions upon geometry and materials were limited providing more accurate results. Such interface was found to facilitate the design of implants providing a verification tool of current and custom-made implant designs based on real patient data.

Medical Imaging, Finite Element Analysis, Computer Aided Analysis and Rapid Prototyping is presented as an integrated approach that can be used for the realistic modeling and simulation of various body structures and the design of implants. It is also possible to use the developed procedures within a hospital environment and introduce new ways of visualizing and using medical scanner data. The identified method can be applied for diagnosis and preoperative planning of complex pathologies, design and verification of implants and educational purposes.

Application of a software system for the development of a three-dimensional finite element model of the knee joint using Magnetic Resonance Imaging (MRI) data

Three-dimensional models are necessary for the realistic finite element analysis (FEA) of joints and implants, but the development of such models has always been time consuming and laborious as far it concerns the extraction of accurate geometry and the distinction between different joint tissues. Interfacing directly medical imaging data to a FEA environment can improve the biomechanical analysis of joints and the design process of orthopedic implants providing very useful geometric information on various tissues and facilitating the development of the three dimensional models.

A new methodology allowing the direct interface between medical scanners and engineering software is applied for the development of a three-dimensional finite element model of the knee joint. Magnetic Resonance images are used in order to obtain geometric information upon the joint tissues and to visualize them in three dimensions. The geometry of different tissue types is extracted and represented by different volumetric entities within a FEA environment. In such a way it has been possible to represent the imaged structures in an accurate way and to assign easily different material properties limiting many assumptions.

The developed model can be used for the realistic analysis of various issues of the knee joint. Total knee replacement designs can be combined with real patient data. The procedure followed can be used to model and analyze accurately other joints and their implants. The model development method is suggested as an important tool for the three-dimensional modeling of joints and as an improved design process for joint replacements.

The Interface of Medical Imaging, Finite Element Analysis (FE A), and Computer Aided Design (CAD) and Rapid Prototyping (RP): The knee, hip and shoulder joints as case studies

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 FEAICAD 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.

The development of a Rapid Prototyping (RP) model of the shoulder joint

The use of anatomical data produced by Rapid Prototyping is gaining increasing acceptance and it often constitutes a decisive step in surgical planning. Identifying a practical method for the development of rapid prototyping joint models would he invaluable in the design of implants or the pre-operative planning of complex pathologies.

A user-friendly method is utilized for the development of RP models of body structures. CT data representing a shoulder joint is acquired using a conventional hospital scanner. The medical imaging data is interfaced into an image processing software for the segmentation and three-dimensional visualization of the joint. The developed three-dimensional computer model is treated as a tool for the extraction of geometrical information of the joint. The anatomical information is exported in a format acceptable by a Rapid Prototyping system and the relevant computer file is imported into a Stereo lithography system. The system builds the model of the described anatomical structure layer by layer until it is complete. The final product is a real model, accurate copy, of the shoulder joint originally scanned.

The developed model can be used to provide a clear picture of the current clinical situation, to simulate a possible intervention or to serve as a tool for the design of custom-made implant. Applying the followed procedure, similar rapid prototyping models can be developed for various anatomical structures. Such models can be used for a variety of applications: three-dimensional visualization of a specific anatomy, surgical planning, implant or prosthesis design.

The Interface of Medical Imaging, CAD/FEA and Rapid Prototyping: Medical Applications

Computer techniques are being increasingly used for the solution of the many problems associated with Biomedical Engineering. In orthopedics, computer and finite element methods have been applied extensively and with much success in the analysis of implants. However, as the expectation for total joint replacement continues to increase, a refinement of the joints' design is demanded.

State-of-the-art engineering design and analysis techniques are utilized. Work is currently done in collaboration with orthopedic companies, surgeons, and radiologists in establishing an automated method for interfacing Medical imaging data (CT and MRI) to a CAD/FEM environment. There is also a great interest to integrate Medical Imaging and Rapid Prototyping in order to obtain real models of any body structures, therefore assisting in surgical planning. The developed techniques are also applied in other medical areas. Developed rapid prototyping models have already assisted in cranio-facial surgeries and there is an interest to introduce the system in a hospital environment.

The projects are assisting in the validation of the developed computer modeling methods for different medical applications, but in particular, in orthopedics for the investigation of particular implant issues and the design of custom-made implants. It is intended to develop 3D computer models of various joints, which could be interfaced in CAD or FEA. Such models could also be used for surgical planning and the accurate overall positioning of implant components. If successful the method could be integrated to a computer-assisted system for the development of individual patient models on site.

The purpose of this project is to reconstruct the geometric characteristics of the hard tissues of the shoulder joint and generate a three-dimensional finite element model. Emphasis is given to the solution of practical difficulties that may exist when interfacing imaging data to a CAD/FEA environment.

Computer Modeling and Medical Rapid Prototyping of Soft Tissues

MRI images are used in order to visualize the soft tissues of the knee joint in 3D. The developed computer model will be interfaced to Rapid Prototyping. The aim of the project is to comment on the possible uses of the applied technology for the modeling and rapid prototyping of soft tissues and on the problems that are faced.

A FEA model of the Hip Joint - Implant Design Performance

The aim of the project is to develop an advanced three-dimensional FEA model of the hip joint that can be used as a computational tool to hip joint biomechanics and to prosthetic implant analysis. The model is to be used for performance predictions of total hip designs.

Computer Modeling of the Elbow Joint - Custom Made Implants

A 3D CAD model of the elbow is to be developed directly from CT images. The developed model will be interfaced to a Medical Rapid Prototyping System. The possible use of such models for the design of custom-made implants is particularly important.

The aim of such projects is the processing of CT images for the development of rapid prototyping models of anatomical structures. The developed models assist in preoperational planning. Various projects exist according to the needs of local hospitals.