MRI-based finite element simulation on radiofrequency ablation of thyroid cancer

In order to provide a quantitative disclosure on the RFA (radiofrequency ablation)-induced thermal ablation effects within thyroid tissues, this paper has developed a three-dimensional finite element simulation strategy based on a MRI (magnetic resonance imaging)-reconstructed model. The thermal lesion's growth was predicted and interpreted under two treatment conditions, i.e. single-cooled-electrode modality and two-cooled-electrode system. The results show that the thermal lesion's growth is significantly affected by two factors including the position of RF electrode and thermal–physiological behavior of the breathing airflow. Additional parametric studies revealed several valuable phenomena, e.g. with the electrode's movement, thermal injury with varying severity would happen to the trachea wall. Besides, the changes in airflow mass produced evident effects on the total heat flux of thyroid surface, while the changes in breathing frequency only generated minor effects that can be ignored. The present study provided a better understanding on the thermal lesions of RFA within thyroid domain, which will help guide future treatment of the thyroid cancer.     

Visually Supporting Multiple Needle Placement in Irreversible Electroporation Interventions

Irreversible electroporation (IRE) is a minimally invasive technique for small tumour ablation. Multiple needles are inserted around the planned treatment zone and, depending on the size, inside as well. An applied electric field triggers instant cell death around this zone. To ensure the correct application of IRE, certain criteria need to be fulfilled. The needles' placement in the tissue has to be parallel, at the same depth, and in a pattern which allows the electric field to effectively destroy the targeted lesions. As multiple needles need to synchronously fulfill these criteria, it is challenging for the surgeon to perform a successful IRE. Therefore, we propose a visualization which exploits intuitive visual coding to support the surgeon when conducting IREs. We consider two scenarios: first, to monitor IRE parameters while inserting needles during laparoscopic surgery; second, to validate IRE parameters in post‐placement scenarios using computed tomography. With the help of an easy to comprehend and lightweight visualization, surgeons are enabled to quickly visually detect what needs to be adjusted. We have evaluated our visualization together with surgeons to investigate the practical use for IRE liver ablations. A quantitative study shows the effectiveness compared to a single 3D view placement method.     

Crepuscular rays for tumor accessibility planning

In modern clinical practice, planning access paths to volumetric target structures remains one of the most important and most complex tasks, and a physician's insufficient experience in this can lead to severe complications or even the death of the patient. In this paper, we present a method for safety evaluation and the visualization of access paths to assist physicians during preoperative planning. As a metaphor for our method, we employ a well-known, and thus intuitively perceivable, natural phenomenon that is usually called crepuscular rays. Using this metaphor, we propose several ways to compute the safety of paths from the region of interest to all tumor voxels and show how this information can be visualized in real-time using a multi-volume rendering system. Furthermore, we show how to estimate the extent of connected safe areas to improve common medical 2D multi-planar reconstruction (MPR) views. We evaluate our method by means of expert interviews, an online survey, and a retrospective evaluation of 19 real abdominal radio-frequency ablation (RFA) interventions, with expert decisions serving as a gold standard. The evaluation results show clear evidence that our method can be successfully applied in clinical practice without introducing substantial overhead work for the acting personnel. Finally, we show that our method is not limited to medical applications and that it can also be useful in other fields.     

Visual Support for Interactive Post‐Interventional Assessment of Radiofrequency Ablation Therapy

Percutaneous radiofrequency (RF) ablation is a minimally invasive, image‐guided therapy for the treatment of liver tumors. The assessment of the ablation area (coagulation) is performed to verify the treatment success as an essential part of the therapy. Traditionally, pre‐ and post‐interventional CT images are used to visually compare the shape, size, and position of tumor and coagulation. In this work, we present a novel visualization as well as a navigation tool, the so‐called tumor map. The tumor map is a pseudo‐cylindrical mapping of the tumor surface onto a 2D image. It is used for a combined visualization of all ablation zones of the tumor to allow a reliable therapy assessment. Additionally, the tumor map serves as an interactive tool for intuitive navigation within the 3D volume rendering of the tumor vicinity as well as with familiar 2D viewers.     

Sensitivity analysis of critical parameters affecting the efficacy of microwave ablation using Taguchi method

Microwave ablation (MWA) is a minimally invasive thermal treatment modality that has already evolved as a promising alternative to radiofrequency ablation for treating different types of malignant and benign tumors, especially ≥3 cm in diameter. The efficacy of thermal ablative therapies is mainly judged by the ablation volume attained post‐ablation. In this regards, the present study aims at analyzing the influence of six critical parameters, as follows, relative permittivity, electrical conductivity, volumetric heat capacity, thermal conductivity, blood perfusion rate, and applied power on the ablation volume attained during MWA. Taguchi's L27 orthogonal array has been adopted for the current problem with six input variables having three levels each. The electric and thermophysical properties considered in the study have been derived from liver, lung, breast, and kidney. Finite element method (FEM) based numerical simulations of MWA have been conducted on three‐dimensional homogeneous model of biological tissue using coaxial single slot microwave antenna. Further, the ranking and the contribution of each parameter on the ablation volume attained during MWA have been quantified using analysis of variance. The corollaries drawn from the study would be useful to the clinical practitioners during the treatment planning stage of the MWA.     

A multi-front eikonal model of cardiac electrophysiology for interactive simulation of radio-frequency ablation

Virtual reality-based therapy simulation meets a growing interest from the medical community due to its potential impact for the training of medical residents and the planning of therapies. However, computer models of the human anatomy are often very computationally demanding, thus incompatible with the constraints of such interactive simulations.In this paper, we propose a fast model of the cardiac electrophysiology based on an eikonal formulation implemented with an anisotropic fast marching method. We demonstrate the use of this model in the context of a simulator of radio-frequency ablation of cardiac arrhythmia from patient-specific medical imaging data. Indeed, this therapy can be very effective for patients but still suffers from a rather low success rate. Being able to test different ablation strategies on a patient-specific model can have a great clinical impact.In our setting, thanks to a haptic 3D user interface, the user can interactively measure the local extracellular potential, pace locally the myocardium or simulate the burning of cardiac tissue as done in radio-frequency ablation interventions.     

基于运动平衡点的水下机器人自主避障方式

当前大多数水下机器人的实时避障方式只简单地考虑了目标和障碍物之间的相对距 离,并没有考虑实际的海洋环境以及会不会对控制器产生不利的影响．本文研究的目的就是 从实际出发,通过设定各个自由度上的运动平衡点,将水下机器人的自主避障规划和运动控 制结合起来,设计出一个集目标、障碍物和控制性能一体的避障规划方式,从仿真实验结果 来看,机器人可以安全地通过障碍空间,到达目的地．     

Effective visualization of complex vascular structures using a non-parametric vessel detection method

The effective visualization of vascular structures is critical for diagnosis, surgical planning as well as treatment evaluation. In recent work, we have developed an algorithm for vessel detection that examines the intensity profile around each voxel in an angiographic image and determines the likelihood that any given voxel belongs to a vessel; we term this the "vesselness coefficient" of the voxel. Our results show that our algorithm works particularly well for visualizing branch points in vessels. Compared to standard Hessian based techniques, which are fine-tuned to identify long cylindrical structures, our technique identifies branches and connections with other vessels. Using our computed vesselness coefficient, we explore a set of techniques for visualizing vasculature. Visualizing vessels is particularly challenging because not only is their position in space important for clinicians but it is also important to be able to resolve their spatial relationship. We applied visualization techniques that provide shape cues as well as depth cues to allow the viewer to differentiate between vessels that are closer from those that are farther. We use our computed vesselness coefficient to effectively visualize vasculature in both clinical neurovascular x-ray computed tomography based angiography images, as well as images from three different animal studies. We conducted a formal user evaluation of our visualization techniques with the help of radiologists, surgeons, and other expert users. Results indicate that experts preferred distance color blending and tone shading for conveying depth over standard visualization techniques.     

Toolpath planning algorithm for the ablation process using energy sources

Ablation processes using various energy sources such as lasers, electrical power and ultrasonic sources have been widely used in industry to ablate workpieces made of hard-to-cut and temperature resistive materials. Even though the cutting mechanism of the ablation process is different from that of the mechanical cutting process, an identical toolpath of the mechanical cutting process has been applied to the ablation process. An inappropriate toolpath for the ablation process may result in a lower dimensional accuracy of the ablated part. Therefore, a new toolpath planning algorithm considering the characteristics of the energy source is required. In this paper, a toolpath planning algorithm for the ablation process is proposed. The proposed algorithm consists of three steps: (1) The generation of a valid toolpath element, (2) the storage of toolpath elements and the creation of sub-groups, (3) the linking of sub-groups. New guidelines on the toolpath demanded by the ablation process are studied. A new idea involving the use of a storage matrix is applied to the storage of toolpath elements and the creation of sub-groups. In order to verify the applicability of the proposed algorithm, the proposed toolpath planning algorithm has been implemented and tested with practical examples.     

OpenLMD,an open source middleware and toolkit for laser-based additive manufacturing of large metal parts

We describe OpenLMD, a novel open-source toolkit for on-line multimodal monitoring and process control of Laser Metal Deposition (LMD). Building on existing open-source libraries (e.g. ROS, OpenCV, PCL), it enables the orchestration and virtualization of a robot cell for LMD and laser materials processing in general. It allows fast and intuitive process programming and planning, easy integration of multiple sensors and equipment, real-time process control, process virtualization and advanced visualization, and web-based interoperability. The approach adopted presents clear advantages in terms of scalability, and multimodal monitoring and data sharing capabilities. OpenLMD speeds up the deployment of laser metal deposition cells that feature CAD-based programming, advanced monitoring and control functionalities, and high interoperability. Its adoption allows focusing on a specific problem, without giving away functionalities that are important for performance demonstration. It facilitates collaborative research and the creation of datasets and benchmarks, in close-to-industrial settings. The ultimate goal is to enable working solutions for fully automated 3D printing of large metal parts, the challenging objective of many recent efforts on process modelling, monitoring, and control.     

Robot Motion Planning in Dynamic Uncertain Environments

In the real world, mobile robots often operate in dynamic and uncertain environments. Therefore, it is necessary to develop a motion planner capable of real-time planning that also addresses uncertainty concerns. In this paper, a new algorithm, Dynamic AO* (DAO*), is developed for navigation tasks of mobile robots. DAO* not only performs a good anytime behavior and offers a fast replanning framework, but also considers the motion uncertainty. Moreover, by incorporating DAO* with D* Lite, a new planning architecture, DDAO*, is represented to efficiently search in large state spaces. Finally, simulations and experiments are shown to verify the efficiency of the proposed algorithms.     

Projector placement planning for high quality visualizations on real-world colored objects

Many visualization applications benefit from displaying content on real-world objects rather than on a traditional display (e.g., a monitor). This type of visualization display is achieved by projecting precisely controlled illumination from multiple projectors onto the real-world colored objects. For such a task, the placement of the projectors is critical in assuring that the desired visualization is possible. Using ad hoc projector placement may cause some appearances to suffer from color shifting due to insufficient projector light radiance being exposed onto the physical surface. This leads to an incorrect appearance and ultimately to a false and potentially misleading visualization. In this paper, we present a framework to discover the optimal position and orientation of the projectors for such projection-based visualization displays. An optimal projector placement should be able to achieve the desired visualization with minimal projector light radiance. When determining optimal projector placement, object visibility, surface reflectance properties, and projector-surface distance and orientation need to be considered. We first formalize a theory for appearance editing image formation and construct a constrained linear system of equations that express when a desired novel appearance or visualization is possible given a geometric and surface reflectance model of the physical surface. Then, we show how to apply this constrained system in an adaptive search to efficiently discover the optimal projector placement which achieves the desired appearance. Constraints can be imposed on the maximum radiance allowed by the projectors and the projectors' placement to support specific goals of various visualization applications. We perform several real-world and simulated appearance edits and visualizations to demonstrate the improvement obtained by our discovered projector placement over ad hoc projector placement.     

Accurate Simulation of RF MEMS VCO performance including phase noise

A new coupled circuit and electrostatic/mechanical simulator (COSMO) is presented for the design of low phase noise radio frequency (RF) microelectromechanical systems (MEMS) voltage-controlled oscillators (VCOs). The numerical solution of device level equations is used to accurately compute the capacitance of a MEMS capacitor. This coupled with a circuit simulator facilitates the simulation of circuits incorporating MEMS capacitors. In addition, the noise from the MEMS capacitor is combined with a nonlinear circuit-level noise analysis to determine the phase noise of RF MEMS VCO. Simulations of two different MEMS VCO architectures show good agreement with experimentally observed behavior.     

Streaming simplification of tetrahedral meshes

Unstructured tetrahedral meshes are commonly used in scientific computing to represent scalar, vector, and tensor fields in three dimensions. Visualization of these meshes can be difficult to perform interactively due to their size and complexity. By reducing the size of the data, we can accomplish real-time visualization necessary for scientific analysis. We propose a two-step approach for streaming simplification of large tetrahedral meshes. Our algorithm arranges the data on disk in a streaming, I/O-efficient format that allows coherent access to the tetrahedral cells. A quadric-based simplification is sequentially performed on small portions of the mesh in-core. Our output is a coherent streaming mesh which facilitates future processing. Our technique is fast, produces high quality approximations, and operates out-of-core to process meshes too large for main memory     

Image Registration for Digital Subtraction Angiography

In clinical practice, Digital Subtraction Angiography (DSA) is a powerful technique for the visualization of blood vessels in the human body. The diagnostic relevance of the images is often reduced by artifacts which arise from the misalignment of successive images in the sequence, due to patient motion. In order to improve the quality of the subtraction images, several registration techniques have been proposed. However, because of the required computation times, it has never led to algorithms that are fast enough so as to be acceptable for integration in clinical applications. In this paper, a new approach to the registration of digital angiographic images is proposed. It involves an edge-based selection of control points for which the displacement is computed by means of template matching, and from which the complete displacement vector field is constructed by means of interpolation. The final warping of the images according to the calculated displacement vector field is performed real-time by graphics hardware. Experimental results with several clinical data sets show that the proposed algorithm is both effective and very fast.     

采用八叉树和OSG分页结点的海量点云三维可视化

针对现有海量点云可视化方法存在索引构建时间长、内存占用大等问题，研究一种八叉树索引结合OSG分页结点的快速可视化方法，可在占用较小内存的基础上快速建立点云索引并实时调度。采用八叉树索引结构对海量点云进行数据组织，建立各层级的八叉树结点并以文件映射的方式分块保存，对结点文件重组织转换为支持OSG渲染引擎的多分辨率点云数据。采用基于OSG分页结点的实时调度技术，对海量点云进行高质量可视化。与目前两款主流的点云数据处理商业软件进行实验对比分析，结果表明所提方法具有索引建立速度快、内存占用小等优点，同时可视化交互更加流畅，适用于各种配置计算机下海量点云数据的调度管理与实时可视化。     

基于影像引导的计算机辅助肝癌微波消融

为了方便临床医生使用医学影像进行手术的规划和引导,提出了一种新颖的计算机辅助肝癌微波消融手术方法.采用基于GPU加速的三维可视化技术实时重构影像的三维模型,显示出患者器官的解剖关系;采用基于生物传热学的三维热场计算技术,规划手术路径及消融设备的作用时间和功率.经过大量的临床应用以及手术影像对比,表明该方法能够有效计算消融手术的作用效果,并在手术的引导过程中发挥了重要的作用,提高了手术的临床精度和效果.     

移动机器人自主导航系统及上位机软件设计与实现

针对移动机器人自主导航系统,采用C++语言设计了一款基于Qt的跨平台实时数据可视化上位机软件;该软件执行SLAM技术和路径规划算法,实现可视化移动机器人建图与导航过程以及实时读取数据参数等功能;首先介绍移动机器人的硬件结构和功能;其次给出了自主导航所运用到的改进RRT*算法和动态窗口法;在详细叙述上位机软件工作流程的基础上,开发和设计了实时话题显示、读取以及界面可视化等功能;最后基于ROS系统完成移动机器人自主导航功能,并通过实时地图与数据可视化来验证所设计上位机软件功能的有效性。     

Real-time Visualization of Brain Electrical Activity

New visualization methods can improve understanding of complex scientific phenomena, such as the brain electrical activity. Real-time execution facilitates assessment of genuine dynamics of brain operation. This paper presents methods for visualization of the brain electrical activity, and real-time implications of the standard computer implementation. The authors present essential trade-off and lessons learned during the realization of two different EEG visualization environments. Real-time visualization provides assessment of genuine brain dynamics, and perception of inherent spatio-temporal patterns of brain electrical activity.