Real-Time Error Control for Surgical Simulation Bui, Huu Phuoc; Tomar, Satyendra; Courtecuisse, Hadrien ...
IEEE transactions on biomedical engineering,
03/2018, Letnik:
65, Številka:
3
Journal Article
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Objective: To present the first a posteriori error-driven adaptive finite element approach for real-time simulation, and to demonstrate the method on a needle insertion problem. Methods: We use ...corotational elasticity and a frictional needle/tissue interaction model. The problem is solved using finite elements within SOFA.1 For simulating soft tissue deformation, the refinement strategy relies upon a hexahedron-based finite element method, combined with a posteriori error estimation driven local h-refinement. Results: We control the local and global error level in the mechanical fields (e.g., displacement or stresses) during the simulation. We show the convergence of the algorithm on academic examples, and demonstrate its practical usability on a percutaneous procedure involving needle insertion in a liver. For the latter case, we compare the force- displacement curves obtained from the proposed adaptive algorithm with that obtained from a uniform refinement approach. Conclusions: Error control guarantees that a tolerable error level is not exceeded during the simulations. Local mesh refinement accelerates simulations. Significance: Our work provides a first step to discriminate between discretization error and modeling error by providing a robust quantification of discretization error during simulations.
We present the corotational cut Finite Element Method (FEM) for real-time surgical simulation. The only requirement of the proposed method is a background mesh, which is not necessarily conforming to ...the boundaries/interfaces of the simulated object. The details of the surface, which can be directly obtained from binary images, are taken into account by a multilevel embedding algorithm which is applied to elements of the background mesh that are cut by the surface. Dirichlet boundary conditions can be implicitly imposed on the surface using Lagrange multipliers, whereas traction or Neumann boundary conditions, which is/are applied on parts of the surface, can be distributed to the background nodes using shape functions. The implementation is verified by convergences studies, of the geometry and of numerical solutions, which exhibit optimal rates. To verify the reliability of the method, it is applied to various needle insertion simulations (e.g. for biopsy or brachytherapy) into brain and liver models. The numerical results show that, while retaining the accuracy of the standard FEM, the proposed method can (1) make the discretisation independent from geometric description, (2) avoid the complexity of mesh generation for complex geometries, and (3) provide computational speed suitable for real-time simulations. Thereby, the proposed method is very suitable for patient-specific simulations as it improves the simulation accuracy by automatically, and properly, taking the simulated geometry into account, while keeping the low computational cost.
•CutFEM enables real-time simulation of needle insertion in soft tissue.•Optimal convergence rates are achieved.•The method captures the geometry in the limit where the mesh tends to zero.•A simple numerical integration algorithm is proposed.•The method provides force versus displacement insertion profiles which are comparable to fitted finite element methods.
With the lattice element method, it is required to introduce a length via, for example, a non-local approach in order to satisfy the objectivity of the mechanical response. In spite of this, the ...mesoscale structuring of inclusions within a matrix conveys the natural origin of the internal length for a fixed mesh. In other words, internal length is not explicitly provided to the model, but rather governed by the characteristics of the meso-structure itself. This study examines the influence that the meso-structure of quasi-brittle materials, like concretes, have on the width of the fracture process zone and thus the fracture energy. The size of the fracture process zone is assumed to correlate with a microstructural dimension of the quasi-brittle material. If a weakness is introduced by a notch, the involvement of the ligament size (a structural parameter) is also investigated. These analyses provide recommendations and warnings that could be beneficial when extracting, from material meso-structures, a required internal length for nonlocal damage models. Among the observations made, the study suggests that the property that best characterise a meso-structure length would be the spacing between inclusions rather than the size of the inclusions themselves. It is also shown that microstructural dimension and the width of the fracture process zone have comparable order of magnitude, and they trend similarly with respect to microstructural sizes such as the inclusion interdistances.
Teachers in elementary schools play a crucial role in educating children about sustainable development. Therefore, the concept of sustainable development is essential for elementary pre-service ...teachers to be ready for their future careers. This study used the sequential mixed methods design to investigate the relationship between the sustainable development perspectives of elementary pre-service teachers in Southern Vietnam and the current teacher training curriculum. The EDINSOST sustainability questionnaire was distributed to 392 participants in order to measure four dimensions of sustainable development: critical contextualization of knowledge, sustainable use of resources, participation in community processes, and ethics. A set of six interview questions was conducted with eight participants, focused on their understandings of sustainable development and the evaluation of the curriculum on sustainable development. Quantitative findings revealed that elementary pre-service teachers rate moderately on all dimensions; however, the knowledge is slightly higher than the behavior. Moreover, there were variations in perspectives based on pre-service teachers’ grade level and gender. Qualitative findings suggested the lack of sustainable development perspectives amongst pre-service teachers and the gaps in the teacher training curriculums regarding sustainable development. Finally, detailed discussions regarding the implementation of sustainable development in the training curriculum were provided.
•Framework for quantifying the discretization error in soft-tissue simulation.•DWR technique for goal-oriented a posteriori error estimation.•Active properties of the soft-tissue (simplified).•Two ...numerical examples inspired from clinical applications.
Errors in biomechanics simulations arise from modelling and discretization. Modelling errors are due to the choice of the mathematical model whilst discretization errors measure the impact of the choice of the numerical method on the accuracy of the approximated solution to this specific mathematical model. A major source of discretization errors is mesh generation from medical images, that remains one of the major bottlenecks in the development of reliable, accurate, automatic and efficient personalized, clinically-relevant Finite Element (FE) models in biomechanics. The impact of mesh quality and density on the accuracy of the FE solution can be quantified with a posteriori error estimates. Yet, to our knowledge, the relevance of such error estimates for practical biomechanics problems has seldom been addressed, see Bui et al. (2018). In this contribution, we propose an implementation of some a posteriori error estimates to quantify the discretization errors and to optimize the mesh. More precisely, we focus on error estimation for a user-defined quantity of interest with the Dual Weighted Residual (DWR) technique. We test its applicability and relevance in three situations, corresponding to experiments in silicone samples and computations for a tongue and an artery, using a simplified setting, i.e., plane linearized elasticity with contractility of the soft tissue modeled as a pre-stress. Our results demonstrate the feasibility of such methodology to estimate the actual solution errors and to reduce them economically through mesh refinement.
An error‐controlled mesh refinement procedure for needle insertion simulations is presented. As an example, the procedure is applied for simulations of electrode implantation for deep brain ...stimulation. We take into account the brain shift phenomena occurring when a craniotomy is performed. We observe that the error in the computation of the displacement and stress fields is localised around the needle tip and the needle shaft during needle insertion simulation. By suitably and adaptively refining the mesh in this region, our approach enables to control, and thus to reduce, the error whilst maintaining a coarser mesh in other parts of the domain. Through academic and practical examples we demonstrate that our adaptive approach, as compared with a uniform coarse mesh, increases the accuracy of the displacement and stress fields around the needle shaft and, while for a given accuracy, saves computational time with respect to a uniform finer mesh. This facilitates real‐time simulations. The proposed methodology has direct implications in increasing the accuracy, and controlling the computational expense of the simulation of percutaneous procedures such as biopsy, brachytherapy, regional anaesthesia, or cryotherapy. Moreover, the proposed approach can be helpful in the development of robotic surgeries because the simulation taking place in the control loop of a robot needs to be accurate, and to occur in real time.
An error‐controlled mesh refinement procedure for needle insertion simulations is presented. We demonstrate that, through simulations of electrode implantation for deep brain stimulation, the proposed methodology has a great potential in terms of simulation accuracy while saving computational efforts and thus facilitates real‐time simulations. Moreover, the proposed approach can be helpful in the development of robotic surgeries because the simulation taking place in the control loop of a robot needs to be accurate, and to occur in real time.
•V2O5 nanomaterials can be synthesized in 5 min, impurity-free.•Synthesized V2O5 nanoparticles can detect 1 ppm NH3 at room temperature.•The sensor’s response is not affected by humidity.
We ...introduce a process for synthesizing V2O5 nano particles directly from vanadium powder using a microwave oven in just 5 min. These nanoparticles are oval-shaped with an average diameter of 9 nm. These V2O5 nanoparticles are capable of detecting 1 ppm NH3 at room temperature with the response of 1.16 and the response/recovery times of 15 s and 326 s, respectively. Notably, the NH3 sensing characteristics of these V2O5 nanoparticles are almost unaffected by the humidity in the air and remain unchanged after at least 60 days of measurement. Therefore, V2O5 nanoparticles synthesized using microwave techniques are a material with great potential for application as low-energy NH3 sensors.
This paper examines the relationships between macroscopic determinants (typically, monetary policies) and microscopic factors (mainly, cash flows and other controlling variables) on corporate ...investment. By employing system-GMM estimation for the 250 Vietnamese non-financial firms, the authors find that the expansionary monetary policy not only encourages the borrowing activities but also results in more corporate investment activities over the period from 2006 to 2016. Noticeably, the internal cash flow is also significant factor, which enhances the activities of corporate investment. Finally, there are differences between internal cash flow effects on corporate investments between two groups, divided by three theoretical criteria. To recapitulate, our implications highlight the importance of monetary policy stability for sustainable growth in corporate investment in Vietnam.
The dynamics of the flux flow in the mixed state of high-
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superconductor interacting with an artificial pinning array is considered. We calculate analytically the current density for the case of ...when the number of vortices outnumbers that of the pinning centers using the time-dependent Ginzburg-Landau equations in a magnetic field in the presence of strong thermal fluctuations. Our results show that the current density increases considerably with increasing pinning strength. It means that an original property of superconductor is recovered even in strong thermal fluctuations under a magnetic field by adding a pinning array to the mixed state of superconductor.
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