Comparative of Techniques: Activation by Sequence, Morph Target Animation and CG/HLSL Programming in Surgery Incision Simulation for Virtual Reality

In this decade, the way of simulating medical scenarios has evolved considerably, for some years now, this area and virtual reality came together giving life to a much more immersive form of simulation. The great challenge in medical simulation is to achieve a consid-erable level of realism and performance, as it is limited by the complexity of the scenario and other factors, the hardware factor being the main limiting. Giving the user the possibility to choose between greater or less realism requires that it be defined with which technique it would be achieved, therefore, this research com-pares three forms of surgical incision simulation for virtual reality: Activation by Sequence, Morph Target Animation and CG/HLSL Programming, evaluating factors such as: frames per-second (fps), CPU and GPU usage, which helped to obtain the level of realism of each technique; resulting in that CG/HLSL Programming uses fewer resources, with 27% CPU usage, 5% integrated GPU, 45% dedicated GPU, 60 fps and 44.3% realism, continuing, with an intermediate level use of resources Activation by Sequence with 11% CPU usage, 18% integrated GPU, 57% dedicated GPU, 60 fps, providing 46.5% realism, finally, the technique that used the most resources and obtained the highest level of realism was Morph Target Animation with 23% CPU usage, 22% integrated GPU, 77% dedicated GPU, 53 fps and 51.3% realism; these techniques can be used depending on the objective of the project where more or less realism is required, considering the use of hardware resources

Interactively Cutting and Constraining Vertices in Meshes Using Augmented Matrices

We present a finite-element solution method that is well suited for interactive simulations of cutting meshes in the regime of linear elastic models. Our approach features fast updates to the solution of the stiffness system of equations to account for real-time changes in mesh connectivity and boundary conditions. Updates are accomplished by augmenting the stiffness matrix to keep it consistent with changes to the underlying model, without refactoring the matrix at each step of cutting. The initial stiffness matrix and its Cholesky factors are used to implicitly form and solve a Schur complement system using an iterative solver. As changes accumulate over many simulation timesteps, the augmented solution method slows down due to the size of the augmented matrix. However, by periodically refactoring the stiffness matrix in a concurrent background process, fresh Cholesky factors that incorporate recent model changes can replace the initial factors. This controls the size of the augmented matrices and provides a way to maintain a fast solution rate as the number of changes to a model grows. We exploit sparsity in the stiffness matrix, the right-hand-side vectors and the solution vectors to compute the solutions fast, and show that the time complexity of the update steps is bounded linearly by the size of the Cholesky factor of the initial matrix. Our complexity analysis and experimental results demonstrate that this approach scales well with problem size. Results for cutting and deformation of 3D linear elastic models are reported for meshes representing the brain, eye, and model problems with element counts up to 167,000; these show the potential of this method for real-time interactivity. An application to limbal incisions for surgical correction of astigmatism, for which linear elastic models and small deformations are sufficient, is included

Direct modification of FE meshes preserving group information

Nowadays, the mainstream methodology for product behavior analysis and improvement relies on the fol-lowing steps: 1) conceptual solution proposal and CAD prototyping, 2) mesh model creation for Finite Element (FE) analysis, 3) preparation of complex mesh model as specification of semantic information for particular behavior study, 4) advanced FE simu-lation, 5) result analysis and optimization loops. The semantics relative to the simulation model are often associated to mesh entities through the use of so-called mesh groups. During the optimization phase, geometric modifications are generally performed on the CAD model. This requires a complete updating of the FE mesh model repeating all the above listed FE mesh preparation (re-creation of all the groups). In the present paper, we propose a new framework for CAD-less FE analysis. It comes to apply shape modi-fication operators directly to the FE mesh while ex-ploiting and maintaining the available FE semantic information. As a result, multiple steeps of the design process loop, as CAD and mesh model generation, mesh group creation, are avoided. In this paper, we focus on two 3D mesh modification operators: the planar cracking and the drillin

GPU Implementation of extended total Lagrangian explicit (gpuXTLED) for Surgical Incision Application

An extended total Lagrangian explicit dynamic (XTLED) is presented as a potential numerical method for simulating interactive or physics-based surgical incisions of soft tissues. The simulation of surgical incision is vital to the integrity of virtual reality simulators that are used for immersive surgical training. However, most existing numerical methods either compromise on computational speed for accuracy or vice versa. This is due to the challenge of modelling nonlinear behaviour of soft tissues, incorporating incision and subsequently updating topology to account for the incision. To tackle these challenges, XTLED method which combines the extended finite element method (XFEM) using total Lagrangian formulation with explicit time integration method was developed. The algorithm was developed and deformations of 3D geometries under tension, were simulated. An attempt was made to validate the XTLED method using silicon samples with different incision configuration and a comparison was made between XTLED and FEM. Results show that XTLED could potentially be used to simulate interactive soft tissue incision. However, further quantitative verification and validation are required. In addition, numerical analyses conducted show that solutions may not be obtainable due to simulation errors. However, it is unclear whether these errors are inherent in the XTLED method or the algorithm created for the XTLED method in this thesis

Direct Modification of Semantically-Enriched Finite Element Meshes

Behaviour analysis loop is largely performed on virtual product model before its physical manufacturing. The last avoids high expenses in terms of money and time spent on intermediate manufacturing. It is gainful from the reality to the virtuality but the process could be further optimized especially during the product behaviour optimization phase. This process involves repetition of four main processing steps: CAD design and modification, mesh creation, Finite Element (FE) model generation with the association of physical and geometric data, FE Analysis. The product behaviour analysis loop is performed on the first design solution as well as on the numerous successive product optimization loops. Each design solution evaluation necessitates the same time as required for the first product design that is particularly crucial in the context of maintenance. In this paper we propose a new framework for CAD-less product optimisation through FE analysis which reduces the model preparation activities traditionally required for FE model creation. More concretely, the idea is to directly operate on the firstly created FE mesh, enriched with physical/geometric semantics, to perform the product modications required to achieve its optimised version. In order to accomplish the proposed CAD-less FE analysis framework, modification operators acting on both the mesh geometry and the associated semantics need to be devised. In this paper we discuss the underlying concepts and present possible components for the development of such operators. A high-level operator specification is proposed according to a modular structure that allows an easy realisation of different mesh modication operators. Here, two instances of this high-level operator are described: the planar cracking and the drilling. The realised prototypes validated on industrial FE models show clearly the feasibility of this approach

Real-time hybrid cutting with dynamic fluid visualization for virtual surgery

It is widely accepted that a reform in medical teaching must be made to meet today's high volume training requirements. Virtual simulation offers a potential method of providing such trainings and some current medical training simulations integrate haptic and visual feedback to enhance procedure learning. The purpose of this project is to explore the capability of Virtual Reality (VR) technology to develop a training simulator for surgical cutting and bleeding in a general surgery

Direct modification of semanticaly-enriched finite element meshes

International audienceBehaviour analysis loop is largely performed on virtual product model before its physical manufacturing. The last avoids high expenses in terms of money and time spent on intermediate manufacturing. It is gainful from the reality to the virtuality but the process could be further optimized especially during the product behaviour optimization phase. This process involves repetition of four main processing steps: CAD design and modification, mesh creation, Finite Element (FE) model generation with the association of physical and geometric data, FE Analysis. The product behaviour analysis loop is performed on the rst design solution as well as on the numerous successive product optimization loops. Each design solution evaluation necessitates the same time as required for the first product design that is particularly crucial in the context of maintenance. In this paper we propose a new framework for CAD-less product optimisation through FE analysis which reduces the model preparation activities traditionally required for FE model creation. More concretely, the idea is to directly operate on the rstly created FE mesh, enriched with physical/geometric semantics, to perform the product modi cations required to achieve its optimised version. In order to accomplish the proposed CAD-less FE analysis framework, modification operators acting on both the mesh geometry and the associated semantics need to be devised. In this paper we discuss the underlying concepts and present possible components for the development of such operators. A high-level operator speci cation is proposed according to a modular structure that allows an easy realisation of di erent mesh modification operators. Here, two instances of this high-level operator are described: the planar cracking and the drilling. The realised prototypes validated on industrial FE models show clearly the feasibility of this approach

Development of Interactive Simulator for Telepresence Robot in Surgical Applications

The purpose of this Diploma thesis is to develop and implement an interactive simulator for a surgical robot in a Telepresence application. The focus is on an incision procedure of a scalpel during an operation. The geometric deformation of the simulation is based on a Finite Element Method (FEM) model which has to cope with discontinuity due to the incision through the body. The FEM modelling can be done using e.g. FEM with remeshing method or XFEM which treats the cut in the body as a type of material discontinuity. A detailed analyse of the eXtended Finite Element Method (XFEM) and a comparison to the FEM with remeshing is made. For the implementation of simulation, a FEM remeshing method is used. A scalpel mounted to the end effector of a robot is controlled by a Haptic device and cuts through a silicone block. The deformation of the real test object are measured by a 2D scanning device and compared to the results of the simulation. The deviation of the reality and simulation were less than 1% based on the dimension of the body

Modelling rock slope behaviour and evolution with reference to Northern Spain and Southern Jordan

The geomorphological behaviour of steep jointed rock slopes has been studied using distinct element computer models. In order to model steep slopes effectively, methodologies need to be combined from the studies of environmental modellers, geomorphologists and engineers. The distinct element method is ideal for the study of the development of jointed rock masses, where the failure is controlled by the nature of the discontinuities. Theoretical modelling identified that block size is a key control affecting the deformation of rock masses. Deformation of rock masses with smaller block assemblages is greater than for rock masses composed of larger block sizes. This is due to the increased magnitude of joint normal closure. Catastrophic failure is less likely in slopes with smaller block sizes because the shear strength is greater in a closely jointed rock mass. These slopes are more likely to undergo gradual deformations. Block-size effects are also responsible for influencing the failure mechanism of rock masses. As block size decreases, the magnitude of block rotation increases and the failure mechanism changes from sliding to toppling. The effect of slope scale on the deformation properties of the rock masses has also been investigated. Two field locations, the Picos de Europa mountains, northern Spain and Wadi Rum, southern Jordan, have been chosen to provide a link between the theoretical modelling and classic rock landforms which are controlled by the discontinuity geometry. Given the sporadic and infrequent occurrence of failure events at the field sites, a computer modelling approach has been adopted to analyse slope behaviour. In the Picos de Europa, slope deformations are deep-seated, with sliding and toppling being the dominant modes of failure. Much of the slope deformation in these mountains is a result of post-glacial rock-slope deformation. The sandstone inselbergs of Jordan show a range of morphologies from rounded hills to vertical cliffs. The morphology of the inselbergs is related to the intact rock strength; stronger Red lshrin sandstone forms vertical slopes, whereas the weaker Disi sandstone forms rounded domes. Jointing in the area is sub-vertical with horizontal bedding and computer simulations have shown that toppling is the dominant mode of failure in these inselbergs. Comparison of computer model output suggests that different failure mechanisms have distinct failure signatures. Catastrophic, deep-seated failures are characterised by a long period of acceleration as the failure propagates through the rock mass and infinite velocity is reached. Non-catastrophic slope movements, such as self-stabilising topples, are characterised by short periods of acceleration followed by small creep movements at a constant velocity. Computer modelling has indicated that scale effects do exist in the modelled rock masses from the Picos de Europa and particularly Wadi Rum. In areas where jointing is constant, the relative block size of the rock mass decreases as slope scale increases. The greater numbers of blocks along with greater in situ stresses influence the failure of the slope. Cosmogenic dating was used to temporally constrain UDEC model output and provide a better understanding of rock slope failure mechanisms in the Picos de Europa and Wadi Rum. Dating indicated delayed paraglacial adjustment was the triggering mechanism for slope failure in the Picos de Europa, whereas failures in Wadi Rum appeared to be closely linked with wetter climatic conditions