This paper describes an adaptive octree cube refinement method for deformable organ models. Surgical simulation is one of the most promising ways for surgical training. Various types of surgical simulators have been researched and developed. Laparoscopic surgery simulators are already in practical use. They have been evaluated for their effectiveness in learning surgical techniques. To realize a high-quality simulator, it is important to efficiently process organ deformation models according to the content of the surgical simulation so that both high-resolution and real-time processing. In this study, we extend adaptive mesh refinement, which increases mesh resolution in the manipulation region, and apply it to an octree cube structure. The refinement process of the octree cube structure is performed based on the distance from the grasping position of the gallbladder model. This approach improves the resolution of the octree in the area near the grasping position where relatively large deformations occur. In addition, it makes it easier to detect interference between the grasp model and the high-resolution grid of the octree. Simulation results showed that there were 199 cubes before and 339 cubes after refinement, and the FPS decreased from 44.1 FPS to 32.4 FPS on a standard CPU and GPU PC, which is still within real-time processing.
This paper proposes a deformable tissue model that introduces octree lattice vertex layout and cubic constraints to the orthodox PBD (Position Based Dynamics) method. Surgical simulation is expected to provide a safe method for training in surgery, which is especially useful for preoperative education of inexperienced surgeons and/or for the case a prior attempt is required. To build a surgical simulator, it is necessary to develop organ models with deformations and interaction algorithms between surgical instruments and organ models, all of which must be performed in real time. Since existing surgical simulators focus on real-time performance, the resolution of organ models is limited. The proposed method restricts the vertex locations of the PBD method to the vertices of the octree lattice to save computation time while maintaining a high deformation resolution. To obtain appropriate results even for large deformations, three-dimensional constraints are applied to each octree cube as the constraints of the PBD method. In the simulations, we tested the overall deformation by dropping a liver model and the local deformation scene by laparoscopic clipping. As a result, we achieved deformation simulations at 26.5 fps for the model with approximately 2,672 cube elements and 20,659 vertices.
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