Nuestros investigadores

Iker Aguinaga Hoyos

Publicaciones científicas más recientes (desde 2010)

Autores: Leizea, I.; Mendizabal, A.; Alvarez, H.; et al.
ISSN 0272-1716  Vol. 37  Nº 1  2017  págs. 56 - 68
One of the most challenging problems in robot-assisted surgical systems is to provide surgical realism at interactive simulation rates. The proposed visual tracking system can track and register object deformations in real time using a physically based formulation, despite the occlusions produced by the robotic system itself. The results obtained provide an accurate visual representation of the deformed solid and will thus enable new assistance approaches to help surgeons during surgical procedures.
Autores: Mendizabal, A.; Aguinaga, Iker;
ISSN 1751-6161  Vol. 45  Nº 5  2015  págs. 1 - 10
Interactive surgical simulators capable of providing a realistic visual and haptic feedback to users are a promising technology for medical training and surgery planification. However, modelling the physical behaviour of human organs and tissues for surgery simulation remains a challenge. On the one hand, this is due to the difficulty to characterise the physical properties of biological soft tissues. On the other hand, the challenge still remains in the computation time requirements of real-time simulation required in interactive systems. Real-time surgical simulation and medical training must employ a sufficiently accurate and simple model of soft tissues in order to provide a realistic haptic and visual response. This study attempts to characterise the brain tissue at similar conditions to those that take place on surgical procedures. With this aim, porcine brain tissue is characterised, as a surrogate of human brain, on a rotational rheometer at low strain rates and large strains. In order to model the brain tissue with an adequate level of accuracy and simplicity, linear elastic, hyperelastic and quasi-linear viscoelastic models are defined. These models are simulated using the ABAQUS finite element platform and compared with the obtained experimental data. (C) 2015 Elsevier Ltd. All rights reserved.
Autores: Aguinaga, Iker; et al.
ISSN 0272-1716  Vol. 34  Nº 3  2014  págs. 12 - 18
Autores: Aguinaga, Iker; et al.
ISSN 1077-2626  Vol. 20  Nº 11  2014  págs. 1555 - 1565
Deformable models are widely used in many disciplines such as engineering and medicine. Real objects are usually scanned to create models in such applications. In many cases the shape of the object is extracted from volumetric data acquired during the scanning phase. At the same time, this volume can be used to define the model's appearance. In order to achieve a visualization that unifies the shape (physical model) and appearance (scanned volume) specially adapted volume rendering techniques are required. One of the most common volumetric visualization techniques is ray casting, which also enables the use of different corrections or improvements such as adaptive sampling or stochastic jittering. This paper presents an extensive study about a ray casting method for tetrahedral meshes with an underlying structured volume. This allows a direct visualization of the deformed model without losing the information contained in the volume. The aim of this study is to analyse and compare the different methods for ray traversal and illumination correction, resulting in a comprehensive relation of the different methods, their computational cost and visual performance.
Autores: San-Vicente, G; Aguinaga, Iker;
ISSN 1077-2626  Vol. 18  Nº 2  2012  págs. 228-241
Mass-Spring Models (MSMs) are used to simulate the mechanical behavior of deformable bodies such as soft tissues in medical applications. Although they are fast to compute, they lack accuracy and their design remains still a great challenge. The major difficulties in building realistic MSMs lie on the spring stiffness estimation and the topology identification. In this work, the mechanical behavior of MSMs under tensile loads is analyzed before studying the spring stiffness estimation. In particular, the performed qualitative and quantitative analysis of the behavior of cubical MSMs shows that they have a nonlinear response similar to hyperelastic material models. According to this behavior, a new method for spring stiffness estimation valid for linear and nonlinear material models is proposed. This method adjusts the stress-strain and compressibility curves to a given reference behavior. The accuracy of the MSMs designed with this method is tested taking as reference some soft-tissue simulations based on nonlinear Finite Element Method (FEM). The obtained results show that MSMs can be designed to realistically model the behavior of hyperelastic materials such as soft tissues and can become an interesting alternative to other approaches such as nonlinear FEM.
Autores: Gutierrez, L.F.; Aguinaga, Iker; Harders, M.; et al.
ISSN 1546-4261  Vol. 23  Nº 42463  2012  págs. 425 - 433
We propose a novel mesh optimization approach that is useful for speeding up a simulation of finite elements-based deformable objects. The approach is based on a quality metric derived from the critical simulation time step of explicit time integration schemes (i.e., the stability limit for the integration of dynamic equations). Our mesh smoothing approach consists of a set of small and independent spring systems. These are made up of a reference mesh node connected to a set of fixed endpoints, which represent the positions that maximize the time step of the elements adjacent to that node. The reference node is displaced to an equilibrium position through a few local iterations. Each spring's stiffness is weighted depending on the quality of its corresponding element. All spring systems can be computed in parallel. Global iterations update the mesh and spring systems. In addition, we combine our smoothing algorithm with topological transformations. With this approach, the simulation performance could be increased by more than 30% depending on the mesh. This approach is suitable for the generation of finite element method meshes, particularly those requiring interactive applications and haptic rendering. Copyright (C) 2012 John Wiley & Sons, Ltd.
Autores: Fierz, B.; Spillmann, J.; Aguinaga, Iker; et al.
ISSN 1077-2626  Vol. 18  Nº 5  2012  págs. 717 - 728
We present a novel hybrid method to allow large time steps in explicit integrations for the simulation of deformable objects. In explicit integration schemes, the time step is typically limited by the size and the shape of the discretization elements as well as by the material parameters. We propose a two-step strategy to enable large time steps for meshes with elements potentially destabilizing the integration. First, the necessary time step for a stable computation is identified per element using modal analysis. This allows determining which elements have to be handled specially given a desired simulation time step. The identified critical elements are treated by a geometric deformation model, while the remaining ones are simulated with a standard deformation model ( in our case, a corotational linear Finite Element Method). In order to achieve a valid deformation behavior, we propose a strategy to determine appropriate parameters for the geometric model. Our hybrid method allows taking much larger time steps than using an explicit Finite Element Method alone. The total computational costs per second are significantly lowered. The proposed scheme is especially useful for simulations requiring interactive mesh updates, such as for instance cutting in surgical simulations.
Autores: Aguinaga, Iker; Fierz, B.; Spillmann, J.; et al.
ISSN 0079-6107  Vol. 103  Nº 42431  2010  págs. 225 - 235
The behavior, performance, and run-time of mechanical simulations in interactive virtual surgery depend heavily on the type of numerical differential equation solver used to integrate in time the dynamic equations obtained from simulation methods, such as the Finite Element Method. Explicit solvers are fast but only conditionally stable. The condition number of the stiffness matrix limits the highest possible time step. This limit is related to the geometrical properties of the underlying mesh, such as element shape and size. In fact, it can be governed by a small set of ill-shaped elements. For many applications this issue can be solved a priori by a careful meshing. However, when meshes are cut during interactive surgery simulation, it is difficult and computationally expensive to control the quality of the resulting elements. As an alternative, we propose to modify the elemental stiffness matrices directly in order to ensure stability. In this context, we first investigate the behavior of the eigenmodes of the elemental stiffness matrix in a Finite Element Method. We then propose a simple filter to reduce high model frequencies and thus allow larger time steps, while maintaining the general mechanical behavior. (C) 2010 Elsevier Ltd. All rights reserved.