The purpose of this study was to develop and validate RetinaVR, an affordable, portable, and fully immersive virtual reality (VR) simulator for vitreoretinal surgery training. We built RetinaVR as a standalone app on the Meta Quest 2 VR headset. It simulates core vitrectomy, peripheral shaving, membrane peeling, and endolaser application. In a validation study (n = 20 novices and experts), we measured: efficiency, safety, and module-specific performance. We first explored unadjusted performance differences through an effect size analysis. Then, a linear mixed-effects model was used to isolate the impact of age, sex, expertise, and experimental run on performance. Experts were significantly safer in membrane peeling but not when controlling for other factors. Experts were significantly better in core vitrectomy, even when controlling for other factors (P = 0.014). Heatmap analysis of endolaser applications showed more consistent retinopexy among experts. Age had no impact on performance, but male subjects were faster in peripheral shaving (P = 0.036) and membrane peeling (P = 0.004). A learning curve was demonstrated with improving efficiency at each experimental run for all modules. Repetition also led to improved safety during membrane peeling (P = 0.003), and better task-specific performance during core vitrectomy (P = 0.038), peripheral shaving (P = 0.011), and endolaser application (P = 0.043). User experience was favorable to excellent in all spheres. RetinaVR demonstrates potential as an affordable, portable training tool for vitreoretinal surgery. Its construct validity is established, showing varying performance in a way that correlates with experimental runs, age, sex, and level of expertise. Fully immersive VR technology could revolutionize surgical training, making it more accessible, especially in developing nations.

Psychophysiological indicators have garnered significant interest in the assessment of presence. However, despite this interest, the nature of the relationship between psychophysiological indicators and presence factors remains undetermined. Presence, the perceived realness of a mediated or virtual experience, is modulated by two factors: immersion and coherence. Immersion represents the extent and precision of the simulated sensory modalities, while coherence refers to the environment's ability to behave as expected by the user. To study the relationship between psychophysiological indicators and presence factors, we objectively manipulated immersion by altering three visual qualities. The visual qualities were set to values above, at, or below their functional threshold. These thresholds are defined as a perceptual boundary under which a sensory quality value should be considered functionally degraded. Sixty participants performed a driving task in a virtual environment under the aforementioned conditions, while we measured their cardiovascular and eye responses. We found that degraded immersion conditions yielded significantly different psychophysiological indicator results than the condition without degradation. However, we observed an effect of immersion degradation on our measured variables only when the visual conditions were set below the functional threshold. Manipulations of immersion below the functional threshold introduced unreasonable circumstances which modified our participants' behavior. Thus, our findings suggest a direct impact of immersion on coherence and highlight the sensitivity of psychophysiological indicators to the coherence of a virtual environment. These results have theoretical implications, as a presence concepts relationship model should include the direct impact of immersion on coherence.

We consider that to objectively measure immersion, one needs to assess how each sensory quality is reproduced in a virtual environment. In this perspective, we introduce the concept of functional threshold which corresponds to the value at which a sensory quality can be degraded without being noticed by the user of a virtual environment. We suggest that the perceived realism of a virtual experience can potentially be evoked for sensory qualities values ranging from the perceptual threshold to the functional threshold. Thus, the identification of functional thresholds values allows us to constrain immersion. To lay the foundation for the identification of functional thresholds, we applied a modified version of the method of limits. We measured the value at which 30 participants were able to identify the degradation of their field of view (FOV), visual acuity, and contrast sensitivity while executing a multidirectional selection test. This enabled us to identify functional perceptual thresholds of 96.6 degrees for FOV, 12.2 arcmin for visual acuity, and 25.6
% for contrast sensitivity.

Simulators for virtual surgery training need to perform complex calculations very quickly to provide realistic haptic and visual interactions with a user. The complexity is further increased by the addition of cuts to virtual organs, such as would be needed for performing tumor resection. A common method for achieving large performance improvements is to make use of the graphics hardware (GPU) available on most general-use computers. Programming GPUs requires data structures that are more rigid than on conventional processors (CPU), making that data more difficult to update. We propose a new method for structuring graph data, which is commonly used for physically based simulation of soft tissue during surgery, and deformable objects in general. Our method aligns all nodes of the graph in memory, independently from the number of edges they contain, allowing for local modifications that do not affect the rest of the structure. Our method also groups memory transfers so as to avoid updating the entire graph every time a small cut is introduced in a simulated organ. We implemented our data structure as part of a simulator based on a meshless method. Our tests show that the new GPU implementation, making use of the new graph structure, achieves a 10 times improvement in computation times compared to the previous CPU implementation. The grouping of data transfers into batches allows for a 80-90% reduction in the amount of data transferred for each graph update, but accounts only for a small improvement in performance. The data structure itself is simple to implement and allows simulating increasingly complex models that can be cut at interactive rates.

Abstract Soft body deformation models are commonly used in surgery simulations. However, cutting those models can have a severe impact on computation times and affects the interactivity of the simulation. We propose a novel method for modeling topology and introducing cuts in a meshless soft body simulated on a background grid, as well a way to progressively update the visual aspect of the object by adding a small number of triangles to the surface mesh to cover the cut area. We determine that the accuracy of the deformation is preserved after cutting by comparing our method to a finite element method. Tests show that this new method achieves interactive simulation rates with more than 10,000 elements while cutting the model and reconstructing the mesh. Our separation of the visual and physical aspects of the simulation allows for more flexibility when tuning the performance of the simulation. Topology modifications have little impact on computation times for either physical or visual changes.

Virtual reality has become a viable tool for training surgeons for specific operations. In order to be useful, such a simulation need to be as realistic as possible so that a user can believe what they experience and act upon the virtual objects. We focus on simulating surgical operations that require cutting virtual organs. They offer a particular set of challenges with respect to simulation stability, performance, robustness and immersion.

In proton therapy, Monte Carlo simulations are desirable to accurately predict the delivered dose. This paper introduces and benchmarks pGPUMCD, a GPU-based Monte Carlo code implementing the physical processes required for proton therapy applications. In pGPUMCD, the proton transport is carried out in a voxelized geometry with a class II condensed history scheme. For this purpose, the equivalent restricted stopping power formalism (Leq formalism), the Fermi-Eyges scattering theory and the discrete electromagnetic/nuclear interactions were considered. pGPUMCD was compared to Geant4 in a validation study where the physical processes were validated one after the other. Dose differences between pGPUMCD and Geant4 were smaller than 1% in the Bragg peak region and up to 3% in its distal fall-off. Moreover, a voxelwise dose difference below 1% was observed for 99.5% of calculation positions. The pGPUMCD 80% falloff positions matched with those of Geant4 within 0.1%. The pGPUMCD computation times were inversely proportional to the voxel size, with one million protons transported in less than 0.5 s with mm3 voxels. pGPUMCD, based on the Leq formalism variance reduction technique, is therefore an attractive candidate for integration in a clinical treatment planning system.

Abstract Despite the growth in research and development in the area of virtual reality over the past few years, virtual worlds do not yet convey a feeling of presence that matches reality. This is particularly due to the difference in visual perception of flat images as compared to actual 3D. We studied the impact of two parameters of the stereoscopic configuration, namely, the inter-camera distance (ICD) and the presence of a depth of field blur (DOF blur). We conducted an experiment involving 18 participants in order to evaluate this impact, based on both subjective and objective criteria. We examined six configurations which differed in the presence or absence of {DOF} blur and the value of the ICD: fixed and equal to the anatomical interpupillary distance, fixed and chosen by the participant, or variable, depending on the depth of the viewer's point of regard (POR). The {DOF} blur and variable {ICD} require the use of an eye tracking system in order to be adjusted with respect to the POR. To our knowledge, no previously published research has tested a gaze-contingent variable {ICD} along with dynamic {DOF} blur in a Cave Automatic Virtual Environment. Our results show that the anatomical and variable {ICD} performed similarly regarding each criterion of the experiment, both being more efficient than the fixed ICD. Besides, as with earlier similar attempts, the configurations with {DOF} blur obtained lower subjective evaluations. Although mainly not significant, the results obtained by the variable {ICD} and {DOF} blur are likely due to a noticeable delay in the parameters update. We also designed a new methodology to objectively compare the geometry and depth rendering, based on the reproduction of the same scene in the real and virtual setups, and then on the study of resulting ocular convergence and angular deviation from a target. This leads to a new comparative criterion for the perceptual realism of immersive virtual environments based on the visual behavior similarity between real and virtual setups.

The purpose of this study was to evaluate the impact of numerical errors caused by the floating point representation of real numbers in a GPU-based Monte Carlo code used for dose calculation in radiation oncology, and to identify situations where this type of error arises. The program used as a benchmark was bGPUMCD. Three tests were performed on the code, which was divided into three functional components: energy accumulation, particle tracking and physical interactions. First, the impact of single-precision calculations was assessed for each functional component. Second, a GPU-specific compilation option that reduces execution time as well as precision was examined. Third, a specific function used for tracking and potentially more sensitive to precision errors was tested by comparing it to a very high-precision implementation. Numerical errors were found in two components of the program. Because of the energy accumulation process, a few voxels surrounding a radiation source end up with a lower computed dose than they should. The tracking system contained a series of operations that abnormally amplify rounding errors in some situations. This resulted in some rare instances (less than 0.1%) of computed distances that are exceedingly far from what they should have been. Most errors detected had no significant effects on the result of a simulation due to its random nature, either because they cancel each other out or because they only affect a small fraction of particles. The results of this work can be extended to other types of GPU-based programs and be used as guidelines to avoid numerical errors on the GPU computing platform.

The aim of this study was to evaluate the potential of bGPUMCD , a Monte Carlo algorithm executed on Graphics Processing Units (GPUs), for fast dose calculations in permanent prostate implant dosimetry. It also aimed to validate a low dose rate brachytherapy source in terms of TG-43 metrics and to use this source to compute dose distributions for permanent prostate implant in very short times. The physics of bGPUMCD was reviewed and extended to include Rayleigh scattering and fluorescence from photoelectric interactions for all materials involved. The radial and anisotropy functions were obtained for the Nucletron SelectSeed in TG-43 conditions. These functions were compared to those found in the MD Anderson Imaging and Radiation Oncology Core brachytherapy source registry which are considered the TG-43 reference values. After appropriate calibration of the source, permanent prostate implant dose distributions were calculated for four patients and compared to an already validated Geant4 algorithm. The radial function calculated from bGPUMCD showed excellent agreement (differences within 1.3%) with TG-43 accepted values. The anisotropy functions at r = 1 cm and r = 4 cm were within 2% of TG-43 values for angles over 17.5°. For permanent prostate implants, Monte Carlo-based dose distributions with a statistical uncertainty of 1% or less for the target volume were obtained in 30 s or less for 1 × 1 × 1 mm 3 calculation grids. Dosimetric indices were very similar (within 2.7%) to those obtained with a validated, independent Monte Carlo code (Geant4) performing the calculations for the same cases in a much longer time (tens of minutes to more than a hour). bGPUMCD is a promising code that lets envision the use of Monte Carlo techniques in a clinical environment, with sub-minute execution times on a standard workstation. Future work will explore the use of this code with an inverse planning method to provide a complete Monte Carlo-based planning solution.

A new hybrid imaging-treatment modality, the MRI-Linac, involves the irradiation of the patient in the presence of a strong magnetic field. This field acts on the charged particles, responsible for depositing dose, through the Lorentz force. These conditions require a dose calculation engine capable of taking into consideration the effect of the magnetic field on the dose distribution during the planning stage. Also in the case of a change in anatomy at the time of treatment, a fast online replanning tool is desirable. It is improbable that analytical solutions such as pencil beam calculations can be efficiently adapted for dose calculations within a magnetic field. Monte Carlo simulations have therefore been used for the computations but the calculation speed is generally too slow to allow online replanning. In this work, GPUMCD, a fast graphics processing unit (GPU)-based Monte Carlo dose calculation platform, was benchmarked with a new feature that allows dose calculations within a magnetic field. As a proof of concept, this new feature is validated against experimental measurements. GPUMCD was found to accurately reproduce experimental dose distributions according to a 2%-2 mm gamma analysis in two cases with large magnetic field-induced dose effects: a depth-dose phantom with an air cavity and a lateral-dose phantom surrounded by air. Furthermore, execution times of less than 15 s were achieved for one beam in a prostate case phantom for a 2% statistical uncertainty while less than 20 s were required for a seven-beam plan. These results indicate that GPUMCD is an interesting candidate, being fast and accurate, for dose calculations for the hybrid MRI-Linac modality.

This paper presents an unsupervised and domain independent semantic analysis that outputs two types of formal representations: discourse representations structures and flat scope-free logical forms. This semantic analysis is built on top of dependency relations produced by a statistical syntactic parser, and is generated by a grammar of patterns named α-grammar. The interest of this grammar lies in building a clear linguistically-grounded syntax-semantic interface using a representation (dependencies) commonly used in the natural language processing community. The paper also explains how semantic representations can be annotated using an upper-level ontology, thus enabling further inference capabilities. The evaluation of the α-Grammar on a hand-made gold standard and on texts from the STEP 2008 Shared Task competition shows the interest of the approach. © 2011 Springer-Verlag.

This paper describes a method to perform automated semantic annotation of named entities contained in large corpora. The semantic annotation is made in the context of the Semantic Web. The method is based on an algorithm that compares the set of words that appear before and after the name entity with the content of Wikipedia articles, and identifies the more relevant one by means of a similarity measure. It then uses the link that exists between the selected Wikipedia entry and the corresponding RDF description in the Linked Data project to establish a connection between the named entity and some URI in the Semantic Web. We present our system, discuss its architecture, and describe an algorithm dedicated to ontological disambiguation of named entities contained in large-scale corpora. We evaluate the algorithm, and present our results. © 2011 Springer-Verlag.

This paper presents a high level view of a project which aims at improving the communication between people who do not share the same language by using a 3D animation upper layer to lift the inherent limitations of written text. We will produce animation using the Collada file format, a standard based on the XML format. This project (GITAN ) has started in January 2010, and we expect to have the first results by the end of 2010. A limited set of sentences will validate the global process and help us refine the tools developed in the pipeline. © Springer-Verlag 2010.

We describe our contribution to the Generation Challenge 2010 for the tasks of Named Entity Recognition and coreference detection (GREC-NER). To extract the NE and the referring expressions, we employ a combination of a Part of Speech Tagger and the Conditional Random Fields (CRF) learning technique. We finally experiment an original algorithm to detect co-references. We conclude with discussion about our system performances.

Scoliosis is a complex deformation of the spine requiring, in severe cases, a highly delicate and invasive surgical instrumentation operation to correct the spinal deformities. Available traditional tools for surgical training have major drawbacks for which virtual reality (VR) technologies and computer simulation can offer solutions. In this paper, we introduce a surgical simulator integrating a complex patient-specific biomechanical model into a VR immersive environment in a collaborative context, the first of its kind for scoliosis surgery training. We present the results for the fully collaborative AVE (audio visual environment) aspects of the simulator. Haptic forces are computed in the biomechanical model, but not yet available as a haptic feedback because of the high forces and torques characteristic of scoliosis surgery, requiring the use of a specifically designed haptic device (in progress). Transatlantic collaborative tests showed that, with our simulator, users on different continents can train collaboratively for scoliosis surgery and visualise the forces and the resulting correction. With the eventual addition of haptic devices, they will also be able to feel the forces remotely. ©2008 IEEE.

This paper describes a proposed architecture and application protocol for the deployment of distributed engineering design tools using emerging WEB-based standards and development tools. The architecture is built around the web services standards and relies on web services orchestration for process execution and control. Various open source software are used and integrated to build the system. The application protocol is obtained using a combination of XML, XML schema and RDF/RDFS languages to define standard data exchange mechanisms between applications. The proposed XML schema and RDFS ontology allow the description of MDA and MDO processes involved in aerospace system design. An example is provided to illustrate the concept.

In this paper we present Wolverine, a simple scene-graph library that incorporates advanced concepts such as node and object differentiation, seamless serialization for distributed environments, and multimedia elements including dynamic textures and video sources. By examining the specifics of Wolverine, we will compare our approach to other scene-graph APIs and dwell on its use in a videoconferencing shared-reality collaborative application. © 2005 by the Massachusetts Institute of Technology.

This study concerns the numerical simulation of airflow and the prediction of comfort properties in a visualisation room of a research centre. Because simulation accuracy depends on the modelling level, special care has been given to fine details. Particular interest has been concentrated on the four-way ceiling air supply diffuser, on the furniture and on the thermal conditions given on computers and on mannequins.The geometric model was created using the parametric features of the pre-processor Gambit, in combination with elements created with the Rhinoceros NURBS modelling tool.Mass, momentum, energy, turbulence, species and radiation conservation equations were solved using Fluent commercial flow solver. Computed airflow and heat transfer parameters were used for numerical prediction of indoor air quality quantities based on ISO 7730. Basic parameters included air temperature, relative humidity and air velocity. These were combined with clothing insulation and metabolic activity measures to obtain standard IAQ indices such as the mean age of air, the predicted mean vote and the predicted percentage of dissatisfied room occupants. Post-processing was carried out with standard Fluent elements and also using Vu, a multi-platform tool which also allows data to be displayed in the Cave immersive environment. © 2004 Elsevier Ltd. All rights reserved.

This study stresses the power of the visual communication language in engineering education and design. The work explores the potential of virtual learning tools aimed to create a new dimension for the study and the understanding of aerodynamics in higher education. For an aerodynamic wing, an hyperspace is defined by selecting geometric and flow variables. It is proposed to study the relation among these variables and their impact on the aerodynamic performance by defining various set and assemblies of three-dimensional subspaces. These spaces are then visualized in the 3D CAVE immersive room opening thus novel paths for the undestanding of the performance of wing aerodynamics with flow and geometric variation. The particular case of airplane wings is presented.

This paper presents the overall architecture of the VADOR application framework. The purpose of the VADOR framework is to enable the seamless integration of commercial and in-house analysis applications in a heterogeneous, distributed computing environment, and to allow the management and sharing of the data in order to provide support to MDO. A multi-tiered client-server architecture has been devised, which comprises a client GUI for interactive data definition and execution launching, separate data and execution servers, and autonomous remotely executable application wrappers. © 2002 by the authors.

This paper presents the overall architecture of the VADOR application framework. The purpose of the VADOR framework is to enable the seamless integration of commercial and in-house analysis applications in a heterogeneous, distributed computing environment, and to allow the deployment of automatic design optimization algorithms based on the framework. A multi-tiered client-server architecture has been devised, which comprises a client GUI for interactive data definition and execution launching, separate data and execution servers, and autonomous remotely executable application wrappers.

This paper discusses the question of data representation as a tool contributing to standardization of complex CFD simulation. Using concepts borrowed from linguistics and language theories, specifications are presented for a declarative representation of complex CFD data including: nodes, computational cells, meshes, as well as scalar, vector and tensor solution fields. © 2001 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

The present paper describes a software framework which addresses an important part of the requirements for a collaborative MDO environment, namely the automation of problem execution and data transfer. The framework is fully written using the JAVA computer language and uses RMI methods in order to be applicable in a heterogeneous and multi-platform environment in a simple and uniform way. This also allows one to use JAVA applets in an internet environment to control processes. Examples are presented in which engineering analysis and design processes are integrated into the framework. Strengths and weaknesses of the present architecture are discussed in relation to the full requirements of an effective MDO environment. © 2000 by the authors.

Body-fitted curvilinear grid generation for the numerical simulation of three dimensional flow in turbomachines is introduced. The grids yield coordinate curves aligned with the domain boundaries. The numerical scheme for the governing equations is carried out on a rectangular mesh, giving a simpler and more accurate algorithm since bondaries coincide with coordinate grids, and no interpolation is required. The geometric complexity, through the transformation, is imbedded into the coefficients of the governing equations, affording the possibility of writing generalized codes applicable to a variety of geometries. This results in a great saving in the code development effort.

Computer-integrated manufacturing of turbomachinery calls for the coordination of three areas: hydraulic or aerodynamic design, mechanical design, and automated fabrication with NC machine tools. The first of these processes, hydraulic or aerodynamic design, can be subdivided into four major steps: geometric modeling; computational modeling; numerical flow simulation; and solution visualization and analysis. This study focuses on the two modeling steps. The authors have developed software for the design of turbomachines, and for the automatic 3-D grid generation used for the subsequent numerical simulation and analysis.

This paper describes a software package tailored for the geometric modelling of turbines, as well as for the automatic generation of a body-fitted coordinate grid. The package consists of four programs used respectively for: 1. The creation and the modification of a model; the designer can 'edit' the model by means of commands whose basic entities are points, profiles, blades, the hub and the shroud. 2. The refinement of the model by the distribution of points over each profile defining the blade, and then by the interpolation of new intermediate profiles between the hub and the shroud. 3. The construction of surfaces delimiting the blade-to-blade channel boundaries (the computational domain). 4. The calculation of a body-fitted coordinate system, inside the channel, by the solution of a system of differential equations. A set of modelled turbines is shown to illustrate the results of each step.