Subset Warping: Rubber Sheeting with Cuts

Image warping, often referred to as "rubber sheeting" represents the deformation of a domain image space into a range image space. In this paper, a technique is described which extends the definition of a rubber-sheet transformation to allow a polygonal region to be warped into one or more subsets of itself, where the subsets may be multiply connected. To do this, it constructs a set of "slits" in the domain image, which correspond to discontinuities in the range image, using a technique based on generalized Voronoi diagrams. The concept of medial axis is extended to describe inner and outer medial contours of a polygon. Polygonal regions are decomposed into annular subregions, and path homotopies are introduced to describe the annular subregions. These constructions motivate the definition of a ladder, which guides the construction of grid point pairs necessary to effect the warp itself

Computational Techniques to Predict Orthopaedic Implant Alignment and Fit in Bone

Among the broad palette of surgical techniques employed in the current orthopaedic practice, joint replacement represents one of the most difficult and costliest surgical procedures. While numerous recent advances suggest that computer assistance can dramatically improve the precision and long term outcomes of joint arthroplasty even in the hands of experienced surgeons, many of the joint replacement protocols continue to rely almost exclusively on an empirical basis that often entail a succession of trial and error maneuvers that can only be performed intraoperatively. Although the surgeon is generally unable to accurately and reliably predict a priori what the final malalignment will be or even what implant size should be used for a certain patient, the overarching goal of all arthroplastic procedures is to ensure that an appropriate match exists between the native and prosthetic axes of the articulation. To address this relative lack of knowledge, the main objective of this thesis was to develop a comprehensive library of numerical techniques capable to: 1) accurately reconstruct the outer and inner geometry of the bone to be implanted; 2) determine the location of the native articular axis to be replicated by the implant; 3) assess the insertability of a certain implant within the endosteal canal of the bone to be implanted; 4) propose customized implant geometries capable to ensure minimal malalignments between native and prosthetic axes. The accuracy of the developed algorithms was validated through comparisons performed against conventional methods involving either contact-acquired data or navigated implantation approaches, while various customized implant designs proposed were tested with an original numerical implantation method. It is anticipated that the proposed computer-based approaches will eliminate or at least diminish the need for undesirable trial and error implantation procedures in a sense that present error-prone intraoperative implant insertion decisions will be at least augmented if not even replaced by optimal computer-based solutions to offer reliable virtual “previews” of the future surgical procedure. While the entire thesis is focused on the elbow as the most challenging joint replacement surgery, many of the developed approaches are equally applicable to other upper or lower limb articulations

A new methodological approach for shoe sole design and validation

Shoe soles are extremely complex to design and manufacture due to their organically shaped but technically precise nature and their manufacturing constraints. Consequently, there is a need for the increased design process flexibility offered by the use of specific CAD methodologies and techniques, to facilitate the work of expert designers and permit effective construction of the three-dimensional elements comprising the complete structure. Recent advances in additive manufacturing systems have extended the possibilities of shoe sole design. These systems can be used to create the final mould and to incorporate dynamic elements that are of particular value in sports footwear. In this article, we present a new methodology for the design and validation of shoe soles. The methodology assists designers in the design concept process and in transfer of the design to manufacturing. The model incorporates both a structural and a functional approach. To this end, a set of specific tools have been developed that can be used to quantify design quality. For example, the model calculates the coefficient of friction or slip resistance, necessary to comply with international standards concerning safety footwear.The financial support of this study comes from IVACE (Instituto Valenciano de Competitividad Empresarial) project: DIHUCA—complex tread designs for footwear soles (IMDEEA/2015/4)

Robust Inside-Outside Segmentation Using Generalized Winding Numbers

Solid shapes in computer graphics are often represented with boundary descriptions, e.g. triangle meshes, but animation, physicallybased simulation, and geometry processing are more realistic and accurate when explicit volume representations are available. Tetrahedral meshes which exactly contain (interpolate) the input boundary description are desirable but difficult to construct for a large class of input meshes. Character meshes and CAD models are often composed of many connected components with numerous selfintersections, non-manifold pieces, and open boundaries, precluding existing meshing algorithms. We propose an automatic algorithm handling all of these issues, resulting in a compact discretization of the input’s inner volume. We only require reasonably consistent orientation of the input triangle mesh. By generalizing the winding number for arbitrary triangle meshes, we define a function that is a perfect segmentation for watertight input and is well-behaved otherwise. This function guides a graphcut segmentation of a constrained Delaunay tessellation (CDT), providing a minimal description that meets the boundary exactly and may be fed as input to existing tools to achieve element quality. We highlight our robustness on a number of examples and show applications of solving PDEs, volumetric texturing and elastic simulation

Efficient techniques for soft tissue modeling and simulation

Performing realistic deformation simulations in real time is a challenging problem in computer graphics. Among numerous proposed methods including Finite Element Modeling and ChainMail, we have implemented a mass spring system because of its acceptable accuracy and speed. Mass spring systems have, however, some drawbacks such as, the determination of simulation coefficients with their iterative nature. Given the correct parameters, mass spring systems can accurately simulate tissue deformations but choosing parameters that capture nonlinear deformation behavior is extremely difficult. Since most of the applications require a large number of elements i. e. points and springs in the modeling process it is extremely difficult to reach realtime performance with an iterative method. We have developed a new parameter identification method based on neural networks. The structure of the mass spring system is modified and neural networks are integrated into this structure. The input space consists of changes in spring lengths and velocities while a "teacher" signal is chosen as the total spring force, which is expressed in terms of positional changes and applied external forces. Neural networks are trained to learn nonlinear tissue characteristics represented by spring stiffness and damping in the mass spring algorithm. The learning algorithm is further enhanced by an adaptive learning rate, developed particularly for mass spring systems. In order to avoid the iterative approach in deformation simulations we have developed a new deformation algorithm. This algorithm defines the relationships between points and springs and specifies a set of rules on spring movements and deformations. These rules result in a deformation surface, which is called the search space. The deformation algorithm then finds the deformed points and springs in the search space with the help of the defined rules. The algorithm also sets rules on each element i. e. triangle or tetrahedron so that they do not pass through each other. The new algorithm is considerably faster than the original mass spring systems algorithm and provides an opportunity for various deformation applications. We have used mass spring systems and the developed method in the simulation of craniofacial surgery. For this purpose, a patient-specific head model was generated from MRI medical data by applying medical image processing tools such as, filtering, the segmentation and polygonal representation of such model is obtained using a surface generation algorithm. Prism volume elements are generated between the skin and bone surfaces so that different tissue layers are included to the head model. Both methods produce plausible results verified by surgeons

Lip syncing method for realistic expressive 3D face model

Lip synchronization of 3D face model is now being used in a multitude of important fields. It brings a more human, social and dramatic reality to computer games, films and interactive multimedia, and is growing in use and importance. High level of realism can be used in demanding applications such as computer games and cinema. Authoring lip syncing with complex and subtle expressions is still difficult and fraught with problems in terms of realism. This research proposed a lip syncing method of realistic expressive 3D face model. Animated lips requires a 3D face model capable of representing the myriad shapes the human face experiences during speech and a method to produce the correct lip shape at the correct time. The paper presented a 3D face model designed to support lip syncing that align with input audio file. It deforms using Raised Cosine Deformation (RCD) function that is grafted onto the input facial geometry. The face model was based on MPEG-4 Facial Animation (FA) Standard. This paper proposed a method to animate the 3D face model over time to create animated lip syncing using a canonical set of visemes for all pairwise combinations of a reduced phoneme set called ProPhone. The proposed research integrated emotions by the consideration of Ekman model and Plutchik’s wheel with emotive eye movements by implementing Emotional Eye Movements Markup Language (EEMML) to produce realistic 3D face model. © 2017 Springer Science+Business Media New Yor

An Image-Based Tool to Examine Joint Congruency at the Elbow

Post-traumatic osteoarthritis commonly occurs as a result of a traumatic event to the articulation. Although the majority of this type of arthritis is preventable, the sequence and mechanism of the interaction between joint injury and the development of osteoarthritis (OA) is not well understood. It is hypothesized that alterations to the joint alignment can cause excessive and damaging wear to the cartilage surfaces resulting in OA. The lack of understanding of both the cause and progression of OA has contributed to the slow development of interventions which can modify the course of the disease. Currently, there have been no reported techniques that have been developed to examine the relationship between joint injury and joint alignment. Therefore, the objective of this thesis was to develop a non-invasive image-based technique that can be used to assess joint congruency and alignment of joints undergoing physiologic motion. An inter-bone distance algorithm was developed and validated to measure joint congruency at the ulnohumeral joint of the elbow. Subsequently, a registration algorithm was created and its accuracy was assessed. This registration algorithm registered 3D reconstructed bone models obtained using x-ray CT to motion capture data of cadaveric upper extremities undergoing simulated elbow flexion. In this way, the relative position and orientation of the 3D bone models could be visualized for any frame of motion. The effect of radial head arthroplasty was used to illustrate the utility of this technique. Once this registration was refined, the inter-bone distance algorithm was integrated to be able to visualize the joint congruency of the ulnohumeral joint undergoing simulated elbow flexion. The effect of collateral ligament repair was examined. This technique proved to be sensitive enough to detect large changes in joint congruency in spite of only small changes in the motion pathways of the ulnohumeral joint following simulated ligament repair. Efforts were also made in this thesis to translate this research into a clinical environment by examining CT scanning protocols that could reduce the amount of radiation exposure required to image patient’s joints. For this study, the glenohumeral joint of the shoulder was examined as this joint is particularly sensitive to potential harmful effects of radiation due to its proximity to highly radiosensitive organs. Using the CT scanning techniques examined in this thesis, the effective dose applied to the shoulder was reduced by almost 90% compared to standard clinical CT imaging. In summary, these studies introduced a technique that can be used to non-invasively and three-dimensionally examine joint congruency. The accuracy of this technique was assessed and its ability to predict regions of joint surface interactions was validated against a gold standard casting approach. Using the techniques developed in this thesis the complex relationship between injury, loading and mal-alignment as contributors to the development and progression of osteoarthritis in the upper extremity can be examined

Modelling, simulation and optimization of a robotic assistive device for patients with spinal cord injury

Robotic gait assistance devices can help the rehabilitation and quality of life of the patients who suffer from spinal cord injury or other neuromuscular disease. The main objective of this bachelor’s thesis in Industrial Technologies Engineering is fo- cused on the obtention of a model of a lower limb exoskeleton and the modelling of the device-user interface contact model in OpenSim which is an open source software de- veloped by the Stanford University. With this model, the final goal pursued is to make predictive simulations of the motion with a biomechanical model of a patient. The results of this thesis can be used to study mechanics involved in a motion of a patient wearing this type of exoskeleton. This thesis contains a relevant background on the topic followed by a practical part where the modelling, simulation and optimization of an exoskeleton is made. The first step is to create a biomechanical model of an exoskeleton using OpenSim. The human body is modelled with a multibody system using rigid bodies. A simple three- dimensional model of a human body formed by 12 bodies simulated as a HAT (head, arms and trunk) is used to add a two bodies exoskeleton. There are three different approaches studied to add this exoskeleton to the human body. Thus, three biomechanical models are created and studied. Secondly, five motions are captured in the UPC Biomechanics Laboratory in order to per- form the kinematic and dynamic simulations in OpenSim. The final practical step is to use the captured motion to study the behaviour of the ex- oskeleton in the laboratory, and then adjust the mechanical parameters set when mod- elling the device-user contact interface. Adjusting the mechanical parameters of the bush- ing forces is not evident. Thus, a methodology to find them is created. Finally, the model found of the exoskeleton is studied dynamically. Predictive simulations are performed with it, where the motion of the exoskeleton is simulated when the motion of a person wearing it is prescribed. The results of this thesis are satisfactory because a fully functional model of an exoskele- ton validated using real data captured from a real motion. The kinematic and dynamic analysis seen in this project show positive results and aim to be a precedent for future studies in this research. Nevertheless, there is still future work to be done testing the exoskeleton on more patients and analysing the results in a wider variety of tests. Fur- thermore, further research on this topic can be done in some areas such as automation of the process of calibrating the mechanical properties of the bushing forces, so more types of exoskeletons can be used