Position-based Dynamics Research Articles

A virtual reality based surgical skills training simulator for catheter ablation with real-time and robust interaction

BackgroundAtrial fibrillation (AF) is the most common sustained cardiac arrhythmia that can cause severe heart problems. Catheter ablation is one of the most ideal procedures for the treatment of AF. Physicians qualified to perform this procedure need to be highly skilled in manipulating the relevant surgical devices. This study proposes an interactive surgical simulator with high fidelity to facilitate efficient training and low-cost medical education. MethodsWe used a shared centerline model to simulate the interaction between multiple surgical devices. An improved adaptive deviation-feedback approach is proposed to accelerate the convergence of each iteration. The periodical beating of the human heart was also simulated in real time using the position-based dynamics (PBD) framework to achieve higher fidelity. We then present a novel method for handling the interaction between the devices and the beating heart mesh model. Experiments were conducted in a homemade simulator prototype to evaluate the robustness, performance, and flexibility of the proposed method. Preliminary evaluation of the simulator was performed by medical students, residents, and surgeons. ResultsThe interaction between surgical devices, static vascular meshes, and beating heart mesh was stably simulated in a frame rate suitable for interaction. ConclusionOur simulator is capable of simulating the procedure of catheter ablation with high fidelity and provides immersive visual experiences and haptic feedback.

Augmented reality-based visual-haptic modeling for thoracoscopic surgery training systems

BackgroundCompared with traditional thoracotomy, video-assisted thoracoscopic surgery (VATS) has less minor trauma, faster recovery, higher patient compliance, but higher requirements for surgeons. Virtual surgery training simulation systems are important and have been widely used in Europe and America. Augmented reality (AR) in surgical training simulation systems significantly improve the training effect of virtual surgical training, although AR technology is still in its initial stage. Mixed reality has gained increased attention in technology-driven modern medicine but has yet to be used in everyday practice. MethodsThis study proposed an immersive AR lobectomy within a thoracoscope surgery training system, using visual and haptic modeling to study the potential benefits of this critical technology. The content included immersive AR visual rendering, based on the cluster-based extended position-based dynamics algorithm of soft tissue physical modeling. Furthermore, we designed an AR haptic rendering systems, whose model architecture consisted of multi-touch interaction points, including kinesthetic and pressure-sensitive points. Finally, based on the above theoretical research, we developed an AR interactive VATS surgical training platform. ResultsTwenty-four volunteers were recruited from the First People's Hospital of Yunnan Province to evaluate the VATS training system. Face, content, and construct validation methods were used to assess the tactile sense, visual sense, scene authenticity, and simulator performance. ConclusionsThe results of our construction validation demonstrate that the simulator is useful in improving novice and surgical skills that can be retained after a certain period of time. The video-assisted thoracoscopic system based on AR developed in this study is effective and can be used as a training device to assist in the development of thoracoscopic skills for novices.

Position-Based Dynamics Simulator of Brain Deformations for Path Planning and Intra-Operative Control in Keyhole Neurosurgery

Many tasks in robot-assisted surgery require planning and controlling manipulators' motions that interact with highly deformable objects. This study proposes a realistic, time-bounded simulator based on Position-based Dynamics (PBD) simulation that mocks brain deformations due to catheter insertion for pre-operative path planning and intra-operative guidance in keyhole surgical procedures. It maximizes the probability of success by accounting for uncertainty in deformation models, noisy sensing, and unpredictable actuation. The PBD deformation parameters were initialized on a parallelepiped-shaped simulated phantom to obtain a reasonable starting guess for the brain white matter. They were calibrated by comparing the obtained displacements with deformation data for catheter insertion in a composite hydrogel phantom. Knowing the gray matter brain structures' different behaviors, the parameters were fine-tuned to obtain a generalized human brain model. The brain structures' average displacement was compared with values in the literature. The simulator's numerical model uses a novel approach with respect to the literature, and it has proved to be a close match with real brain deformations through validation using recorded deformation data of in-vivo animal trials with a mean mismatch of 4.73$\pm$2.15%. The stability, accuracy, and real-time performance make this model suitable for creating a dynamic environment for KN path planning, pre-operative path planning, and intra-operative guidance.

A Lagrangian differencing dynamics method for granular flow modeling

In this paper, a new Lagrangian differencing dynamics (LDD) method is presented for the simulation of granular flows. LDD is a truly meshless method, which employs second-order consistent spatial operators derived from the Taylor expansion and point renormalization. A decoupled pressure-velocity formulation is employed to derive the pressure Poisson equation, which ensures smooth pressure results in time. Granular media are modeled as viscoplastic materials with the Drucker-Prager yield surface. The velocity equation is formulated and solved in an implicit form, in order to handle large viscosities from the constitutive model. Furthermore, a position-based dynamics technique is used to maintain uniform distribution of the Lagrangian points. The presented LDD method for granular flows is validated by simulating two numerical examples. The results are compared with experimental and numerical data from the literature.

A study of real-time simulation of liver of virtual surgical robot based on biologically position-based dynamic model

Virtual surgery robot can accurately modeling of surgical instruments and human organs, and realistic simulation of various surgical phenomena such as deformation of organic tissues, surgery simulation system can provide operators with reusable virtual training and simulation environment. To meet the requirement of virtual surgery robot for the authenticity and real-time of soft tissue deformation and surgical simulation in liver surgery, a new method is proposed to simulate the deformation of soft tissue. This method combines the spring force, the external force of the system, and the constraint force produced by the constraint function of the position-based dynamics. Based on the position-based dynamics, an improved three-parameter mass-spring model is added. In the calculation of the elastic force, the nonlinearity and viscoelasticity of the soft tissue are introduced, and the joint force of the constraint projection process and the constraint force of the position-based dynamics is used to modify mass points movement. The method of position-based dynamics based on biological characteristics, not only considers the biomechanical properties of biological soft tissue as an organic polymer such as viscoelasticity, nonlinearity, and incompressibility but also retains the rapidity and stability of the position based dynamic method. Through the simulation data, the optimal side length of tetrahedral mesh in the improved three-parameter model is obtained, and the physical properties of the model are proved. The real-time simulation of the liver and other organs is completed by using the Geomagic touch force feedback device, which proves the practicability and effectiveness of this method.

Fluid-cloth coupling algorithm based on PBD and CCD

In order to simulate the interaction between cloth and fluid, we use Smooth Particle Hydrodynamics (SPH) as a method in fluid simulation, we propose a Continuous collision detection (CCD) and position-based dynamics (PBD) collision constrained iterative flow coupling method. By analyzing the parallelism of the algorithm, we implement a low storage and load balanced fluid and cloth coupling algorithm parallel computing is used to accelerate the simulation. The experimental results show that our method realizes the bidirectional coupling of fluid and cloth, and improves the simulation performance.

Fast 3D Indoor Scene Synthesis by Learning Spatial Relation Priors of Objects.

We present a framework for fast synthesizing indoor scenes, given a room geometry and a list of objects with learnt priors. Unlike existing data-driven solutions, which often learn priors by co-occurrence analysis and statistical model fitting, our method measures the strengths of spatial relations by tests for complete spatial randomness (CSR), and learns discrete priors based on samples with the ability to accurately represent exact layout patterns. With the learnt priors, our method achieves both acceleration and plausibility by partitioning the input objects into disjoint groups, followed by layout optimization using position-based dynamics (PBD) based on the Hausdorff metric. Experiments show that our framework is capable of measuring more reasonable relations among objects and simultaneously generating varied arrangements in seconds compared with the state-of-the-art works.

Procedural Animation of Freshly Cooked Rice Based on Water Content-Aware XPBD and CDRF Shader

In this paper, we propose a method of reproducing freshly cooked rice using computer graphics animation. The physical properties of freshly cooked rice (rice grains) include shape, density, refractive index, transmittance, and reflectance. Based on these data, the objective is to render the texture and shape of a large amount of cooked rice in a photo-realistic way. Create rice grain polygon models with low resolution based on electron micrographs, rice grains with different shapes and considering the porous structure, we can create a large number of 3D rice grain models. Next, a large number of freshly cooked rice grains were transferred to XPBD (eXtended Position-Based Dynamics), we simulate aggregates by adding a constraint condition. This can be used to simulate the softness of freshly cooked rice. It also allows you to create any shape of rice structure. Finally, the Sub-Surface Scattering (SSS) also takes into account the water content, so that it can be used for the Curvature-dependent reflectance function (CDRF). Depending on the moisture content, different rice grains can be represented with different appearances. With such proposed method, a large number of rice grains are placed in a bowl of freshly cooked rice, rice balls, sushi rice, etc. is represented realistically.

Real-Time Cloth Simulation on Virtual Human Character Using Enhanced Position Based Dynamic Framework Technique

Cloth simulation and animation has been the topic of research since the mid-80's in the field of computer graphics. Enforcing incompressible is very important in real time simulation. Although, there are great achievements in this regard, it still suffers from unnecessary time consumption in certain steps that is common in real time applications. This research develops a real-time cloth simulator for a virtual human character (VHC) with wearable clothing. This research achieves success in cloth simulation on the VHC through enhancing the position-based dynamics (PBD) framework by computing a series of positional constraints which implement constant densities. Also, the self-collision and collision with moving capsules is implemented to achieve realistic behavior cloth modelled on animated characters. This is to enable comparable incompressibility and convergence to raised cosine deformation (RCD) function solvers. On implementation, this research achieves optimized collision between clothes, syncing of the animation with the cloth simulation and setting the properties of the cloth to get the best results possible. Therefore, a real-time cloth simulation, with believable output, on animated VHC is achieved. This research perceives our proposed method can serve as a completion to the game assets clothing pipeline.

Learning to manipulate amorphous materials

We present a method of training character manipulation of amorphous materials such as those often used in cooking. Common examples of amorphous materials include granular materials (salt, uncooked rice), fluids (honey), and visco-plastic materials (sticky rice, softened butter). A typical task is to spread a given material out across a flat surface using a tool such as a scraper or knife. We use reinforcement learning to train our controllers to manipulate materials in various ways. The training is performed in a physics simulator that uses position-based dynamics of particles to simulate the materials to be manipulated. The neural network control policy is given observations of the material (e.g. a low-resolution density map), and the policy outputs actions such as rotating and translating the knife. We demonstrate policies that have been successfully trained to carry out the following tasks: spreading, gathering, and flipping. We produce a final animation by using inverse kinematics to guide a character's arm and hand to match the motion of the manipulation tool such as a knife or a frying pan.

Modelling blast movement and muckpile formation with the position-based dynamics method

ABSTRACT In the bench blasting, rock mass will be fragmented and thrown under the explosion energy. Usually, the movement of the rock fragmentation is of the same importance as the blast fragmentation. The muckpile shape is a manifestation and outcome of the rock fragmentation movement, which is not well interpreted yet. Most existing methods for the rock fragmentation movement are force-based, which are computer time-consuming. In this study, a position-based dynamics (PBD) method is extended to simulate the rock fragmentation movement in production blasting by describing rock mass displacement in a rigid-body dynamics framework. The proposed model discretises the whole rock mass volume into small irregularly shaped blocks using a Voronoi algorithm, and the velocity based on blast energy is assigned to each block. Then, the movement, collision and landing of the blocks are simulated with PBD method. A simulation example of a practical bench blasting case is carried out to validate the PBD method. The movement of the rock fragmentation to form the final muckpile is reproduced and analysed.

Interactive editing of virtual chordae tendineae for the simulation of the mitral valve in a decision support system

PurposeDecision support systems for mitral valve disease are an important step toward personalized surgery planning. A simulation of the mitral valve apparatus is required for decision support. Building a model of the chordae tendineae is an essential component of a mitral valve simulation. Due to image quality and artifacts, the chordae tendineae cannot be reliably detected in medical imaging.MethodsUsing the position-based dynamics framework, we are able to realistically simulate the opening and closing of the mitral valve. Here, we present a heuristic method for building an initial chordae model needed for a successful simulation. In addition to the heuristic, we present an interactive editor to refine the chordae model and to further improve pathology reproduction as well as geometric approximation of the closed valve.ResultsFor evaluation, five mitral valves were reconstructed based on image sequences of patients scheduled for mitral valve surgery. We evaluated the approximation of the closed valves using either just the heuristic chordae model or a manually refined model. Using the manually refined models, prolapse was correctly reproduced in four of the five cases compared to two of the five cases when using the heuristic. In addition, using the editor improved the approximation in four cases.ConclusionsOur approach is suitable to create realistically parameterized mitral valve apparatus reconstructions for the simulation of normally and abnormally closing valves in a decision support system.

Research on anchor chain visualization for a ship anchoring simulation training system.

In the development of ship anchorage training systems, the problems of low efficiency and poor fidelity exist in the simulation of flexible anchor chains, and a position-based dynamics (PBD) method is proposed to express the chain movement. To satisfy the requirements of simulating anchoring manipulation, the PBD method modifies the position of anchor chain particles by controlling constraints. Using the original distance constraint and bending constraint of the PBD approach, two novel constraints, namely, the long-range attachment (LRA) constraint and pin constraint, are developed to simulate the bending and stretching of the anchor chain. Simulation of ordinary ropes can be achieved using distance and bending constraints. The developed LRA constraint is capable of preventing anchor chain particles from being overstretched. Adoption of the pin constraint is proposed to integrate two particles into one to be calculated as an attempt to simulate the connection between the chain and the anchor. The continuous collision detection (CCD) constraint method considering friction and viscosity is used to detect collisions in the ship anchoring training system. Collision detection covers chain collisions with other objects and chains. Finally, the PBD method is more efficient and robust than the Newton method. Since it has sufficient visual plausibility and can realize real-time visualization, the simulation system developed by the PBD method effective for training crew members.

Using position-based dynamics to simulate deformation in aortic valve replacement procedure

Abstract We present a novel approach to simulate deformation in aortic valve replacement scenarios with applications in operation planning and batch domain creation for large computational fluid dynamics studies of the aortic arch.

The PBD Model Based Simulation for Soft Tissue Deformation in Virtual Surgery

With the development of computer technology, surgical simulators based on virtual reality have been widely studied, and the key technology of virtual surgery simulation is deformation. The simulation of soft tissue deformation mainly includes two aspects: (1) Using the appropriate physical model for deformation calculation; (2) The virtual surgery simulation has collision detection, force feedback and so on. In the design of deformation algorithm, the above two problems should be considered at the same time to ensure that the system has high real-time and authenticity. Aiming at the above problems, this paper used the method of position based dynamics (PBD), which can effectively simulate the effect of soft tissue deformation.

Fast Simulation of Cloth-Rigid Body Based on PBD

Because the excellent performance of the position-based dynamics (PBD) method, the PBD gains popularity among cloth simulation and computer animation. Based on unified adaptive PBD, we apply collision constraints to cloth and rigid body models to speed up the process of collision detection between cloth and complex models, we conduct a bounding box high-level collision culling detection algorithm. Moreover,friction is calculated by the speed of the cloth to make the cloth simulation more realistic. Compared with continuous collision detection (CCD), our method improves the simulation speed several times.The experimental results demonstrate that we has the wide range of applicability and the the simulation effect is stable.

Deformable objects modeling with iterative updates of local positions

Background and objectiveDeformation of elastic material such as soft tissues of human body in the virtual environment is computed based on actual material properties. But this often leads to computational overhead hindering real-time simulation. This paper proposes a new modeling method of deformable objects for real-time simulation, using iterative updates of local positions, and control of the desired behavior by material properties. MethodThe Saint Venant–Kirchhoff model is used to form the governing equation to express and control the nonlinear behavior and properties of the material. This governing equation is combined with a local iterative solver using position-based dynamics framework. The proposed method updates the local positions iteratively by finding the solution to minimize the energy of related elements surrounding the target nodes. A grouping method is devised to determine the optimal order of computation. ResultVarious dynamic behaviors can be simulated using the proposed method corresponding to different Young's modulus. Maximum deformations simulated by the proposed method are compared with those results from commercial ANSYS. Relative errors of the real-time simulation results are less than 15% when Young's modulus ranges from 4 kPa to 10 kPa. Real-time performance is evaluated using a liver model composed of 596 tetrahedral elements. ConclusionSimulation results show that the proposed method can simulate, in real-time, the stiffness of the model faithfully according to their material properties.

Position‐Based Simulation of Elastic Models on the GPU with Energy Aware Gauss‐Seidel Algorithm

AbstractIn this paper, we provide a smooth extension of the energy aware Gauss‐Seidel iteration to the Position‐Based Dynamics (PBD) method. This extension is inspired by the kinetic and potential energy changes equalization and uses the foundations of the recent extended version of PBD algorithm (XPBD). The proposed method is not meant to conserve the total energy of the system and modifies each position constraint based on the equality of the kinetic and potential energy changes within the Gauss‐Seidel process of the XPBD algorithm. Our extension provides an implicit solution for relatively better stiffness during the simulation of elastic objects. We apply our solution directly within each Gauss‐Seidel iteration and it is independent of both simulation step‐size and integration methods. To demonstrate the benefits of our proposed extension with higher frame rates, we develop an efficient and practical mesh coloring algorithm for the XPBD method which provides parallel processing on a GPU. During the initialization phase, all mesh primitives are grouped according to their connectivity. Afterwards, all these groups are computed simultaneously on a GPU during the simulation phase. We demonstrate the benefits of our method with many spring potential and strain‐based continuous material constraints. Our proposed algorithm is easy to implement and seamlessly fits into the existing position‐based frameworks.

Combining position-based dynamics and gradient vector flow for 4D mitral valve segmentation in TEE sequences.

For planning and guidance of minimally invasive mitral valve repair procedures, 3D+t transesophageal echocardiography (TEE) sequences are acquired before and after the intervention. The valve is then visually and quantitatively assessed in selected phases. To enable a quantitative assessment of valve geometry and pathological properties in all heart phases, as well as the changes achieved through surgery, we aim to provide a new 4D segmentation method. We propose a tracking-based approach combining gradient vector flow (GVF) and position-based dynamics (PBD). An open-state surface model of the valve is propagated through time to the closed state, attracted by the GVF field of the leaflet area. The PBD method ensures topological consistency during deformation. For evaluation, one expert in cardiac surgery annotated the closed-state leaflets in 10 TEE sequences of patients with normal and abnormal mitral valves, and defined the corresponding open-state models. The average point-to-surface distance between the manual annotations and the final tracked model was [Formula: see text]. Qualitatively, four cases were satisfactory, five passable and one unsatisfactory. Each sequence could be segmented in 2-6min. Our approach enables to segment the mitral valve in 4D TEE image data with normal and pathological valve closing behavior. With this method, in addition to the quantification of the remaining orifice area, shape and dimensions of the coaptation zone can be analyzed and considered for planning and surgical result assessment.

VIPER

We extend the formulation of position-based rods to include elastic volumetric deformations. We achieve this by introducing an additional degree of freedom per vertex -- isotropic scale (and its velocity). Including scale enriches the space of possible deformations, allowing the simulation of volumetric effects, such as a reduction in cross-sectional area when a rod is stretched. We rigorously derive the continuous formulation of its elastic energy potentials, and hence its associated position-based dynamics (PBD) updates to realize this model, enabling the simulation of up to 26000 DOFs at 140 Hz in our GPU implementation. We further show how rods can provide a compact alternative to tetrahedral meshes for the representation of complex muscle deformations, as well as providing a convenient representation for collision detection. This is achieved by modeling a muscle as a bundle of rods, for which we also introduce a technique to automatically convert a muscle surface mesh into a rods-bundle. Finally, we show how rods and/or bundles can be skinned to a surface mesh to drive its deformation, resulting in an alternative to cages for real-time volumetric deformation. The source code of our physics engine will be openly available1.