Sergi Grau

3D reconstruction and quantification of porous structures

In this paper, we describe the methodology that we have designed to quantify the pores distribution in bone implants and the empirical results that we have obtained with BioCAD designed scaffolds, microCT and confocal microscopy data. Our method is based on 3D digital topology properties of the porous structure. We segment the 3D images into three regions: exterior, bone and pore space. Next, we divide the pore space into pores and connection paths. We compute a graph of the pore space such that each node of the graph represents a pore, and an arc between two nodes indicates that the two pores are path-connected. On the basis of the graph and the segmented model, we are able to compute several properties of the material such as global porosity, effective porosity and radial pore distribution.

PREVIRNEC: A cognitive telerehabilitation system based on Virtual Environments

In this paper, we describe PREVIRNEC, a distributed system for cognitive telerehabilitation based on virtual environments. Our system allows personalized treatments by means of 2D and 3D exercises that can be built according to single patients characteristics. Patients realize their exercises remotely. Depending on their obtained results, the system readjusts automatically the levels of difficulty of the tasks, and switches from one task to the other. The paper focuses on technological issues of the system design. We analyze its structure, components, and we discuss the decisions adopted in the interaction mode design and well as in the tasks layout.

Animation of 3D Avatars for Rehabilitation of the Upper Limbs

The paper presents a 3D Virtual Environment (VE) for neurorehabilitation of the upper limb. Patients move one of their arms trying to simulate concrete daily actions, such as grasping a bottle, opening a door or putting a book on a shelve. They wear a special garment that integrates four inertial sensors providing in real time information on the orientation of the patients shoulder, elbow and wrist. The VE is a complete scenario integrating all the objects needed to perform virtually the actions simulated by the patients. In the VE, patients are represented by 3D avatars that, using the data provided by the inertial sensors, reproduce in real time their arm movements. Since only the arm movement is monitorized, but neither the hand nor the trunk and the neck, the system must combine real movements with baked animations in order to show a realistic behavior of the 3D avatar. Moreover, it must take into account collisions between the 3D avatar and the virtual objects. Finally, it must detect when the patient is about to simulate an interaction with an object in order to realize it virtually. We describe the strategies that we have designed to provide these functionalities.

The wise cursor: assisted selection in 3D serious games

In recent years, the evolution of 3D graphics hardware and software has lead to a growing interest for serious games in three-dimensional virtual environments for learning, training, and rehabilitation. Many of these games are based on a first-person-shooter paradigm in which users navigate through the environment, select, and manipulate virtual objects. The target users of these applications are not necessarily usual gamers, and they often have difficulties in navigating and interacting in the 3D environment.This paper proposes the wise cursor, a new method for selection that improves the usability and accessibility of mouse-driven serious games in 3D environments. At each user click, the proposed method computes a list of objects candidates to be selected and their probability of being the desired one. Depending on the uncertainty of the probability distribution, either one object is selected or a mechanism to clarify the selection is proposed. In the former case, if the selected object is within the user avatar’s scope, the action associated to it is realized, otherwise the application automatically navigates toward it. In this way, selection and navigation are eased. The empirical results of the usability tests show that this technique is fast, practical, and that it requires little user’s skills. Thus, it can make serious games usable for a wider range of users who can concentrate on the training objectives without technological barriers.

Design of 3D Virtual Neuropsychological Rehabilitation Activities

Virtual environments can be valid and efficient tools for neuropsychological rehabilitation of cognitive impairments. However,the specification of the virtual task is not easy for neuropsychologists who are not aware of game design and implementation issues. We present the method that we have followed to help therapists to describe the expected task functioning. Our system is split into different subsystems: interactions, task logic, messages,scoring and feedback. This way, therapists specify the requirements of each subsystem separately, which comes out to be easier and clearer. The game structure manages and composes the input and output of the different subsystems to run the game. All the interactions are specified according to a common syntax. This provides the desired flexibility to add, remove and modify interactions in run-time. In order to control the location of all the objects of the scenario, for each receiver surface, we define a pick-and-place grid that keeps record of the objects piled onto it. The game logic is implemented as a non-deterministic automaton that controls each task state, modifies in run-time the different subsystems and programs new interactions.Moreover, we have designed a graphical editor to describe the game logic in a simple way, focusing only on relevant states of the application.

VolumeEVM: A new approach for surface/volume integration

Volume visualization is a very active research area in the field of scientific visualization. The main techniques of volume visualization are surface rendering and direct volume rendering. In recent works, the extreme vertices model (EVM) has been used as an intermediate model to visualize and manipulate volume data using a surface rendering approach. However, the ability to integrate the advantages of surface rendering approaches with the superiority in visual exploration of volume rendering would allow one to obtain a very complete framework for visualization and manipulation of volume data. In this paper, the VolumeEVM is presented as an enhanced EVM-based model. It incorporates the volumetric information required to achieve a nearly direct volume visualization technique. Thus, a new surface/volume integrated model is defined based on the EVM encoding. Also, an algorithm following the splatting technique and using the VolumeEVM has been devised.

A Serious Games platform for early diagnosis of mild cognitive impairments

Smart Aging, a Serious games (SGs) platform in a 3D virtual environment aimed at the early detection of Mild Cognitive Impairments (MCI) in persons ageing between 50 and 80. The navigation in a 3D environment (loft) that simulates in a reduced space the basic elements of interaction of home living, associated with the game approach results in a powerful screening tool, more friendly and motivating with respect to the traditional paper&pencil tests. The Smart Aging platform asks people to perform tasks related to daily activities, closer to real life than traditional paper&pencil tests, and, in doing so, it is able to evaluate different cognitive functions. The platform has been realized through a strong collaboration between game developers, neurologists and neuropsychologists. A scientific validation phase is ongoing on a sample of 1000 users to provide evidence of the efficacy and usefulness of the Smart Aging system.

Exploration of porous structures with illustrative visualizations

The analysis of porous structures from CT images is emerging as a new computer graphics application that is useful in diverse scientific fields such as BioCAD and geology. These structures are very complex and difficult to analyze visually when they are presented with traditional rendering techniques. In this paper, we describe a visualization application based on illustrative techniques for rendering porous structures. We provide various interactive pore selection mechanisms and visualization styles that allow users to better perceive the connectivity between pores and how they are distributed by radii throughout the structure. The application also shows simulations of fluid intrusion or extrusion through the structure, and it allows users to navigate inside. We describe our application and discuss the experimental results with phantom models, BioCAD scaffolds, implants and rock samples. Graphical AbstractWe describe a porous structures visualization application based on illustrative techniques. It provides pore selection mechanisms, different visualization styles, simulations of fluid intrusion, and navigations inside. Display Omitted Research Highlights? The analysis of porous structures can be enhanced using a graphical model. ? A volume model of the structure alone is difficult to explore. ? The combination of a graph connectivity and a volume model provides tools to efficiently explore pore structures. ? The use of illustrative techniques such as cut-away, ghosting, edge enhancement and colormaps provides clues on the pore size and the topological distances between pores.

Ray-casting time-varying volume data sets with frame-to-frame coherence

The goal of this paper is the proposal and evaluation of a ray-casting strategy that takes advantage of the spatial and temporal coherence in image-space as well as in object-space in order to speed up rendering. It is based on a double structure: in image-space, a temporal buffer that stores for each pixel the next instant of time in which the pixel must be recomputed, and in object-space a Temporal Run-Length Encoding of the voxel values through time. The algorithm skips empty and unchanged pixels through three different space-leaping strategies. It can compute the images sequentially in time or generate them simultaneously in batch. In addition, it can handle simultaneously several data modalities. Finally, an on-purpose out-of-core strategy is used to handle large datasets. The tests performed on two medical datasets and various phantom datasets show that the proposed strategy significantly speeds-up rendering.

An Adaptive Cutaway with Volume Context Preservation

Knowledge expressiveness of scientific data is one of the most important visualization goals. However, current volume visualization systems require a lot of expertise from the final user. In this paper, we present a GPU-based ray casting interactive framework that computes two initial complementary camera locations and allows to select the focus interactively, on interesting structures keeping the volumes context information with an adaptive cutaway technique. The adaptive cutaway surrounds the focused structure while preserving a depth immersive impression in the data set. Finally, we present a new brush widget to edit interactively the opening of the cutaway and to graduate the context in the final image.