Physically-based Deformation of High-Resolution 3D Lung Models for Augmented Reality based Medical Visualization

Visualization tools using Augmented Reality Environments are effective in applications related to medical training, prognosis and expert interaction. Such medical visualization tools can also provide key visual insights on the physiology of deformable anatomical organs (e.g. lungs). In this paper we propose a deformation method that facilitates physically-based elastostatic deformations of 3D high-resolution polygonal models. The implementation of the deformation method as a pre-computation approach is shown for a 3D high-resolution lung model. The deformation is represented as an integration of the applied force and the local elastic property assigned to the 3D lung model. The proposed deformation method shows faster convergence to equilibrium as compared to other physically-based simulation methods. The proposed method also accounts for the anisotropic tissue elastic properties. The transfer functions are formulated in such a way that they overcome stiffness effects during deformations

Modeling and grasping of thin deformable objects

Deformable modeling of thin shell-like and other objects have potential application in robot grasping, medical robotics, home robots, and so on. The ability to manipulate electrical and optical cables, rubber toys, plastic bottles, ropes, biological tissues, and organs is an important feature of robot intelligence. However, grasping of deformable objects has remained an underdeveloped research area. When a robot hand applies force to grasp a soft object, deformation will result in the enlarging of the finger contact regions and the rotation of the contact normals, which in turn will result in a changing wrench space. The varying geometry can be determined by either solving a high order differential equation or minimizing potential energy. Efficient and accurate modeling of deformations is crucial for grasp analysis. It helps us predict whether a grasp will be successful from its finger placement and exerted force, and subsequently helps us design a grasping strategy. The first part of this thesis extends the linear and nonlinear shell theories to describe extensional, shearing, and bending strains in terms of geometric invariants including the principal curvatures and vectors, and the related directional and covariant derivatives. To our knowledge, this is the first non-parametric formulation of thin shell strains. A computational procedure for the strain energy is then offered for general parametric shells. In practice, a shell deformation is conveniently represented by a subdivision surface. We compare the results via potential energy minimization over a couple of benchmark problems with their analytical solutions and the results generated by two commercial softwares ABAQUS and ANSYS. Our method achieves a convergence rate an order of magnitude higher. Experimental validation involves regular and freeform shell-like objects (of various materials) grasped by a robot hand, with the results compared against scanned 3-D data (accuracy 0.127mm). Grasped objects often undergo sizable shape changes, for which a much higher modeling accuracy can be achieved using the nonlinear elasticity theory than its linear counterpart. The second part numerically studies two-finger grasping of deformable curve-like objects under frictional contacts. The action is like squeezing. Deformation is modeled by a degenerate version of the thin shell theory. Several differences from rigid body grasping are shown. First, under a squeeze, the friction cone at each finger contact rotates in a direction that depends on the deformable object\u27s global geometry, which implies that modeling is necessary for grasp prediction. Second, the magnitude of the grasping force has to be above certain threshold to achieve equilibrium. Third, the set of feasible finger placements may increase significantly compared to that for a rigid object of the same shape. Finally, the ability to resist disturbance is bounded in the sense that increasing the magnitude of an external force may result in the breaking of the grasp

Non-linear and anisotropic elastic soft tissue models for medical simulation

Best conference paper awardInternational audienceno abstrac

Soft volume simulation using a deformable surface model

The aim of the research is to contribute to the modelling of deformable objects, such as soft tissues in medical simulation. Interactive simulation for medical training is a concept undergoing rapid growth as the underlying technologies support the increasingly more realstic and functional training environments. The prominent issues in the deployment of such environments centre on a fine balance between the accuracy of the deformable model and real-time interactivity. Acknowledging the importance of interacting with non-rigid materials such as the palpation of a breast for breast assessment, this thesis has explored the physics-based modelling techniques for both volume and surface approach. This thesis identified that the surface approach based on the mass spring system (MSS) has the benefits of rapid prototyping, reduced mesh complexity, computational efficiency and the support for large material deformation compared to the continuum approach. However, accuracy relative to real material properties is often over looked in the configuration of the resulting model. This thesis has investigated the potential and the feasibility of surface modelling for simulating soft objects regardless of the design of the mesh topology and the non-existence of internal volume discretisation. The assumptions of the material parameters such as elasticity, homogeneity and incompressibility allow a reduced set of material values to be implemented in order to establish the association with the surface configuration. A framework for a deformable surface model was generated in accordance with the issues of the estimation of properties and volume behaviour corresponding to the material parameters. The novel extension to the surface MSS enables the tensile properties of the material to be integrated into an enhanced configuration despite its lack of volume information. The benefits of the reduced complexity of a surface model are now correlated with the improved accuracy in the estimation of properties and volume behaviour. Despite the irregularity of the underlying mesh topology and the absence of volume, the model reflected the original material values and preserved volume with minimal deviations. Global deformation effect which is essential to emulate the run time behaviour of a real soft material upon interaction, such as the palpation of a generic breast, was also demonstrated, thus indicating the potential of this novel technique in the application of soft tissue simulation

Calcul rapide de forces et de déformations mécaniques non-linéaires et visco-élastiques pour la simulation de chirurgie

Ce travail présente une méthode de calcul rapide de déformations et de forces mécaniques destinée à la simulation d'applications chirurgicales. La simulation de chirurgie vise à offrir aux praticiens des outils leur permettant de pratiquer des entraînements intensifs et de pouvoir planifier avec précision certaines interventions. La conception de tels simulateurs nécessite de disposer de modèles géométriques et mécaniques précis des organes du corps humain, et d'algorithmes de calcul suffisamment rapides pour être capable d'utiliser ces modèles dans des conditions de temps réel. La plupart des simulateurs existants utilisent des modèles mécaniques extrêmement simples, basés sur les lois de l'élasticité linéaire. Or de nombreux résultats de biomécanique indiquent que les tissus biologiques se comportent selon des lois beaucoup plus complexes, incluant des effets non-linéaires et visco-élastiques importants. Pour cette raison, nous avons développé une méthode permettant le calcul rapide de déformations et de forces incluant des effets mécaniques non-linéaires et visco-élastiques. Cette méthode utilise la théorie des éléments finis et a été conçue comme une extension de l'algorithme dit des masses-tenseurs pour l'élasticité linéaire. Son principe consiste à pré-calculer un certain nombre de tenseurs dépendant des caractéristiques géométriques et mécaniques de chaque élément fini, qui sont ensuite combinés dans la phase de simulation proprement dite. Notre modèle non-linéaire ne présage d'aucune forme particulière de loi mécanique, de sorte que la méthode proposée est suffisamment générique pour s'appliquer à une grande variété de comportements et d'objets. Après la description de l'algorithme, de ses performances en terme de temps de calcul et de ses conditions de stabilité numérique, nous démontrons que cette méthode est capable de reproduire avec précision le comportement mécanique d'un tissu biologique mou. Ce travail s'inscrivant plus spécifiquement dans le cadre du développement d'un système de simulation de la cryochirurgie du foie, nous avons étudié expérimentalement les propriétés du foie lors de sa perforation par une aiguille à biopsie. Le modèle de masses-tenseurs non-linéaire et visco-élastique construit à l'aide des paramètres expérimentaux a pu reproduire avec une bonne précision les propriétés observées.This work presents a method for the fast computation of mechanical deformations and forces for the simulation of surgical applications. Surgery simulation aims at providing physicians with tools allowing extensive training and precise planning of given interventions. The design of such simulation systems requires accurate geometrical and mechanical models of the organs of the human body, as well as fast computation algorithms suitable for real-time conditions. Most existing simulation systems use very simple mechanical models, based on the laws of linear elasticity. Numerous biomechanical results yet indicate that biological tissues exhibit much more complex behaviour, including important non-linear and visco-elastic effects. For this reason, we developed a method allowing the fast computation of mechanical deformations and forces including non-linear and visco-elastic effects. This method uses finite element theory and has been constructed as an extension of the so-called tensor-mass algorithm for linear elasticity. It consists in pre-computing a set of tensors depending on the geometrical and mechanical properties of each finite element, which are later combined in the simulation part itself. Our non-linear model does not assume any particular form of mechanical law, so that the proposed method is generic enough to be applied to a wide variety of behaviours and objects. Following the description of the algorithm, of its performances in terms of computation time, and of its numerical stability conditions, we show that this method allows to reproduce the mechanical behaviour of a biological soft tissue with good precision. As this project is part of a broader effort aiming more specifically at developing a simulation system for liver cryosurgery, we experimentally characterized the properties of liver in perforation by a biopsy needle. The non-linear and visco-elastic tensor-mass model constructed from experimental parameters succeeded in accurately reproducing the observed properties

Soft volume simulation using a deformable surface model

The aim of the research is to contribute to the modelling of deformable objects, such as soft tissues in medical simulation. Interactive simulation for medical training is a concept undergoing rapid growth as the underlying technologies support the increasingly more realstic and functional training environments. The prominent issues in the deployment of such environments centre on a fine balance between the accuracy of the deformable model and real-time interactivity. Acknowledging the importance of interacting with non-rigid materials such as the palpation of a breast for breast assessment, this thesis has explored the physics-based modelling techniques for both volume and surface approach. This thesis identified that the surface approach based on the mass spring system (MSS) has the benefits of rapid prototyping, reduced mesh complexity, computational efficiency and the support for large material deformation compared to the continuum approach. However, accuracy relative to real material properties is often over looked in the configuration of the resulting model. This thesis has investigated the potential and the feasibility of surface modelling for simulating soft objects regardless of the design of the mesh topology and the non-existence of internal volume discretisation. The assumptions of the material parameters such as elasticity, homogeneity and incompressibility allow a reduced set of material values to be implemented in order to establish the association with the surface configuration. A framework for a deformable surface model was generated in accordance with the issues of the estimation of properties and volume behaviour corresponding to the material parameters. The novel extension to the surface MSS enables the tensile properties of the material to be integrated into an enhanced configuration despite its lack of volume information. The benefits of the reduced complexity of a surface model are now correlated with the improved accuracy in the estimation of properties and volume behaviour. Despite the irregularity of the underlying mesh topology and the absence of volume, the model reflected the original material values and preserved volume with minimal deviations. Global deformation effect which is essential to emulate the run time behaviour of a real soft material upon interaction, such as the palpation of a generic breast, was also demonstrated, thus indicating the potential of this novel technique in the application of soft tissue simulation.EThOS - Electronic Theses Online ServiceUniversiti Malaysia Sarawak (UMS)Malaysia. Jabatan Perkhidmatan Awam (JPA)Malaysia. Kementerian Pengajian Tinggi (KPT)GBUnited Kingdo