Tao Ruan Wan

A realistic elastic rod model for real-time simulation of minimally invasive vascular interventions

Simulating intrinsic deformation behaviors of guidewire and catheters for interventional radiology (IR) procedures, such as minimally invasive vascular interventions is a challenging task. Especially real-time simulations for interactive training systems require not only the accuracy of guidewire manipulations, but also the efficiency of computations. The insertion of guidewires and catheters is an essential task for IR procedures and the success of these procedures depends on the accurate navigation of guidewires in complex 3D blood vessel structures to a clinical target, whilst avoiding complications or mistakes of damaging vital tissues and blood vessel walls. In this paper, a novel elastic model for modeling guidewires is presented and evaluated. Our interactive guidewire simulator models the medical instrument as thin flexible elastic rods with arbitrary cross sections, treating the centerline as dynamic and the deformation as quasi-static. Constraints are used to enforce inextensibility of guidewires, providing an efficient computation for bending and twisting modes of the physically-based simulation model. We demonstrate the effectiveness of the new model with a number of simulation examples.

A Stable and Real-Time Nonlinear Elastic Approach to Simulating Guidewire and Catheter Insertions Based on Cosserat Rod

Interventional Radiology procedures (e.g., angioplasty, embolization, stent graft placement) provide minimally invasive therapy to treat a wide range of conditions. These procedures involve the use of flexible tipped guidewires to advance diagnostic or therapeutic catheters into a patients vascular or visceral anatomy. This paper presents a real-time physically based hybrid modeling approach to simulating guidewire insertions. The long, slender body of the guidewire shaft is simulated using nonlinear elastic Cosserat rods, and the shorter flexible tip composed of a straight, curved, or angled design is modeled using a more efficient generalized bending model. Therefore, the proposed approach efficiently computes intrinsic dynamic behaviors of guidewire interactions within vascular structures. The efficacy of the proposed method is demonstrated using detailed numerical simulations inside 3-D blood vessel structures derived from preprocedural volumetric data. A validation study compares positions of four physical guidewires deployed within a vascular phantom, with the co-ordinates of the corresponding simulated guidewires within a virtual model of the phantom. An optimization algorithm is also implemented to further improve the accuracy of the simulation. The presented simulation model is suitable for interactive virtual reality-based training and for treatment planning.

Modelling the dynamic drape of garments on synthetic humans in a virtual fashion show

Reports the dynamic modelling of garments on synthetic humans. Develops the model based on a physical analogue to a deep shell system for describing and predicting the real 3‐D shape of clothes. Determines the garment motion by fabric deformation energy, gravity and external constraints of the garment, such as collision forces, using the deformable node bar concept. Justifies the model by agreement between real fabric prediction of static and dynamic drapes using our newly developed drape metre. Demonstrates the garment simulation using garments from two different fabrics in a virtual fashion show. Also describes the work on modelling and animating a synthetic female. The advantages of this model are that engineering parameters can be used as model parameters directly and that the model is configured based on the surface co‐ordinate system, which are important for the next generation of fashion CAD systems incorporating virtual fashion shows. This consideration is fundamental in the context of global retailing and becomes an integral part of intelligent textile and garment manufacture. Proposes the consequences of this work in cinema, TV, advertising and in graphics and animation are also important, but does not examine these.

The Concept of Virtual Measurement

This paper discusses the concept of virtual measurement in textiles and describes the development of a virtual 3D fabric drape measurement system. In this system, a physical based model is used to predict the draping performance, static and dynamic drape of a given fabric sample. Fabric mechanical properties are used for simulating the virtual 3D shape of the fabric samples, which produce a time‐variable deformation of the virtual fabric drape. The 3D fabric drape can be observed under any view angle. An algorithm is developed, applied and integrated into the system for carrying out virtual fabric drape measurements in order to evaluate the drapeability of a given fabric. Important fabric aesthetic attributes such as number of fabric folds, fold variation and depth of fold are presented and implemented together with the drape co‐efficient.

Modelling the dynamic drape of fabrics on synthetic humans: a physical, lumped‐parameter model

True 3‐D garment design (CAD) systems are fundamental for the next generation of intelligent textile and garment manufacture and retailing. Reports a new approach for modelling fabric. The fabric model is developed based on a physical analogue to a deep shell system for describing and predicting the real 3‐D shape of clothes. The fabric motion is determined by deformation energy, gravity and external constraints, such as collision forces, using the deformable node bar concept. The advantages of this model are that engineering parameters can be used as model parameters directly and that the model is configured based on the surface co‐ordinate system, which is believed to be important as the basis of a powerful fashion CAD system. The model successfully simulated fabric drape and has been implemented on a synthetic female model.

A remote, on‐line 3‐D human measurement and reconstruction approach for virtual wearer trials in global retailing

A powerful 3‐D system has been developed for on‐line 3‐D human measurement and reconstruction that interferes with a SQL Server database for virtual wearer trials in global retailing. In this research, 3‐D body profiles have been captured and analysed using an on‐line image measurement and processing system developed in this research and then stored in the database system. A parametric geometric human model has been devised with an effective search algorithm that utilises body measurements obtained on‐line or retrieved from the database. A SQL server database system has been constructed with user friendly interfaces which enables users to collect, manage and analyse all related information including human body images.

Real-time path planning for navigation in unknown environment

Real-time path planning is a challenging task that has many applications in the fields of AI, moving robots, virtual reality, agent behavior simulation, and action games. The various approaches for path planning have different criteria that have to be met, resulting in a number of algorithms for solutions to specific problems. In this paper, we introduce our approach and recent development regarding path planning in game environments. We propose a real-time motion-optimization algorithm called Adaptive Dynamic Points of Visibility (ADPV) for navigation of vehicles or moving agents in dynamical unconfigured environments, which computes a collision-free, time-optimal motion track for the moving objects. Our approach is able to deal with the obstacle-space that is unknown or partially unknown to the moving agent. It therefore solves the drawbacks of traditional obstacle-space configuration methods.

Urban flood risk analysis for determining optimal flood protection levels based on digital terrain model and flood spreading model

The objective of the paper is to present a new risk-analysis approach for the assessment of optimal flood protection levels in urban flood risk management, which is based on an active contour method. Although the active contour method is a very popular research topic, there has been no attempt made on deriving a model for simulating flooding and inundating to date, as far as we are aware. We have developed a flooding prototype system, which consists of two main parts: a digital terrain model and a flood simulation model. The digital terrain model is constructed using real world measurement data of GIS, in terms of digital elevation data and satellite image data. A pyramidal data arrangement structure is used for dealing with the requirements of terrain details with different resolutions. A new flooding model has been developed, which is useful for urban flood simulation. It consists of a flooding image spatial segmentation based on an active contour model, a water level calculation process, a standard gradient descent method for energy minimisation. When testing the 3D flood simulation system, the simulation results are very close to the real flood situation, and this method has faster speed and greater accuracy of simulating the inundation area in comparison to the conventional 2D flood simulation models.

Constraint-Based Soft Tissue Simulation for Virtual Surgical Training

Most of surgical simulators employ a linear elastic model to simulate soft tissue material properties due to its computational efficiency and the simplicity. However, soft tissues often have elaborate nonlinear material characteristics. Most prominently, soft tissues are soft and compliant to small strains, but after initial deformations they are very resistant to further deformations even under large forces. Such material characteristic is referred as the nonlinear material incompliant which is computationally expensive and numerically difficult to simulate. This paper presents a constraint-based finite-element algorithm to simulate the nonlinear incompliant tissue materials efficiently for interactive simulation applications such as virtual surgery. Firstly, the proposed algorithm models the material stiffness behavior of soft tissues with a set of 3-D strain limit constraints on deformation strain tensors. By enforcing a large number of geometric constraints to achieve the material stiffness, the algorithm reduces the task of solving stiff equations of motion with a general numerical solver to iteratively resolving a set of constraints with a nonlinear Gauss-Seidel iterative process. Secondly, as a Gauss-Seidel method processes constraints individually, in order to speed up the global convergence of the large constrained system, a multiresolution hierarchy structure is also used to accelerate the computation significantly, making interactive simulations possible at a high level of details. Finally, this paper also presents a simple-to-build data acquisition system to validate simulation results with ex vivo tissue measurements. An interactive virtual reality-based simulation system is also demonstrated.

A Real-time Dynamic Simulation Scheme for Large-Scale Flood Hazard Using 3D Real World Data

We propose a new dynamic simulation scheme for large-scale flood hazard modelling and prevention. The approach consists of a number of core parts: digital terrain modelling with GIS data, Nona-tree space partitions (NTSP), automatic river object recognition and registration, and a flood spreading model. The digital terrain modelling method allows the creation of a geometric real terrain model for augmented 3D environments with very large GIS data, and it can also use information gathered from aviation and satellite images with a ROAM algorithm. A spatial image segmentation scheme is described for river and flood identification and for a 3D terrain map of flooding region growth and visualisation. The region merging is then implemented by adopting flood region spreading algorithm (FRSA). Compared with the conventional methods, our approach has the advantages of being capable of realistically visualising the flooding in geometrically-real 3D environments, of handling dynamic flood behaviour in real-time and of dealing with very large-scale data modelling and visualisation.