EP4A: Software and Computer Based Simulator Research: Development and Outlook SOFA—An Open Source Framework for Medical Simulation

Abstract

Computer-based training systems offer an elegant solution to the current need for better training in Medicine, since realistic and configurable training environments can be created. However, in spite of the impressive developments in the field of medical simulation, some fundamental problems still hinder the acceptance of this valuable technology in daily clinical practice. In particular, the multidisciplinary aspect of medical simulation requires the integration, within a single environment, of leading-edge solutions in areas as diverse as visualization, biomechanical modeling, haptics, or contact modeling. This diversity of problems makes it challenging for researchers to make progress in specific areas, and leads rather often to duplication of efforts. METHODS For the past few years, there have been a few attempts at designing software toolkits for medical simulation1–4 Although our aim is identical, we propose a different approach, through a very modular and flexible software framework called SOFA (Simulation Open Framework Architecture). This open source framework allows independently developed algorithms to interact together within a common simulation while minimizing the development time required for integration. The main objectives of the SOFA framework are: Provide a common software framework for the medical simulation community Enable component sharing/exchange and reduce development time Promote collaboration among research groups Enable validation and comparison of new algorithms Help standardize the description of anatomic and biomechanical datasets To develop such a flexible framework while minimizing the impact on the computation overhead, we have developed a new and advanced architecture. As a result, it is possible with SOFA to: 1) create complex and evolving simulations by combining new algorithms with algorithms already included in SOFA; 2) modify most parameters of the simulation—deformable behavior, surface representation, solver, constraints, collision algorithm, etc.—by simply editing a XML file; 3) build complex models from simpler ones using a scene-graph description; 4) efficiently simulate the dynamics of interacting objects using abstract equation solvers; 5) reuse and easily compare a variety of available methods. To achieve these objectives, the SOFA architecture relies on several innovative concepts, in particular, the notion of multimodel representation. In SOFA, most simulation components—deformable models, collision models, instruments, etc—can have several representations, connected through a mechanism called mapping. Each representation can then be optimized for a particular task—eg, collision detection, visualization—while improving interoperability by creating a clear separation between the functional aspects of the simulation components. As a consequence, it is possible to have models of very different nature interact together, for instance rigid bodies, deformable objects, and fluids. Several other very innovative concepts have been introduced in the architecture of SOFA, leading to a flexible yet efficient software framework for interactive, physics-based simulation. CONCLUSION The SOFA framework currently integrates, in the same environment, a variety of different algorithms, from springs and corotational FEM models to FFD deformation grids, as well as implicit and explicit solvers, and several collision detection methods, such as continuous or proximity-based algorithms. Our framework also supports hard constraints and stiff interaction forces, using implicit or multistep explicit integrators that handle dynamically created groups of interacting objects. Recent GPU hardware is also supported by SOFA, allowing even faster computation times. Our next objective is the development of 3 complete simulation systems based on SOFA: an interventional radiology simulator, a laparoscopic surgery simulator, and a radio-frequency ablation simulation. The SOFA web site, www.sofaframework.org, can be visited for more information on our most recent results. ACKNOWLEDGMENTS We want to thank Sylvere Fonteneau, Damien Marchal, Xunlei Wu, Paul Neumann, Jeremie Dequidt, and Julien Lenoir for their contribution to the development of SOFA.