基于环境特征和随机方法的柔性针路径规划

针对柔性针软组织穿刺路径规划问题,提出了一种基于环境特征和随机方法的规划算法。该方法采用单轮车模型,运用快速搜索随机树算法得到样本路径,再基于路径长度、弧段数、安全度及障碍物风险分级相结合的路径评估函数,得到最优路径。在路径生成过程中,医生可根据临床经验设置评估函数的权重系数及判断障碍物的风险等级,以适用不同组织的穿刺环境。进行复杂环境下柔性针软组织穿刺路径规划仿真,结果表明该方法环境适用性强,算法交互性好,具有较好的应用潜力。     

自适应SVD–UKF算法及在穿刺状态估计中的应用

柔性针在实际穿刺过程中会产生不规则形变, 导致柔性针模型存在参数不确定性问题, 影响穿刺精度. 本文针对柔性针穿刺过程存在的不确定性问题以及超声成像等设备存在的量测噪声统计特征不准确性问题, 提出了一种带有噪声估计器的自适应奇异值分解无迹卡尔曼滤波算法. 该算法采用自适应因子实时修正动力学模型误差, 通过奇异值分解抑制系统状态协方差矩阵的负定性, 利用Sage-Husa估计器在线估计噪声的统计特性, 减小了系统状态估计误差. 将新算法应用于带有曲率不定性的柔性针穿刺模型进行计算仿真, 仿真结果显示, 新的算法较现有的UKF算法相比, 估计误差减小了0.28 mm(82.7%), 与AUKF算法相比, 估计误差减小0.06 mm(52%). 因此, 新算法可有效改善滤波性能, 提高穿刺状态的估计精度.     

基于多目标粒子群优化算法的斜尖柔性针穿刺路径规划

针对斜尖柔性针在复杂环境下由入针点到达病灶位置的穿刺路径问题,提出一种基于多目标粒子群优化算法(MOPSO)的路径规划方法.对软组织内柔性针运动学模型进行分析,构建控制量与柔性针穿刺路径的关系;分析障碍物约束,建立障碍物约束的数学描述;然后,根据穿刺术的要求将穿刺精度、穿刺危险性和穿刺路径长度作为柔性针穿刺优化目标,将柔性针穿刺路径规划问题转化为多目标优化问题;建立了相应的多目标优化问题的数学模型,使用多目标粒子群优化算法对模型进行优化求解.最后通过仿真实验证明了所提方法的有效性,并仿真分析了穿刺路径的在线修正问题.     

互信息驱动的有限元医学图像配准方法

针对医学图像中软组织形变复杂多样的特点,在配准过程中以离散化的有限单元为基本单位模拟和预测整个弹性体产生的形变,将配准过程视为有限元求解二维平面应力问题并对有限元能量函数进行改进,选取高精度和鲁棒性良好的互信息(MI)为测度应用到方程求解中。为提高算法效率,在配准过程中采用多分辨率策略进行优化。通过对放疗中医学图像进行配准实验并与已有方法进行比较,得到的配准结果更优,对刚体位移更敏感并提高了速度,表明该方法是一种具有高精度和高效率的配准方法。     

有限元指纹图像配准

针对指纹图像中形变复杂多样的特点,对指纹图像配准算法进行研究,发现目前指纹配准算法存在复杂度高,精度低,速度慢,易受指纹形变等影响的缺陷,引入有限元分析理论,提出了有限元指纹图像配准算法。该算法将指纹图像配准中的复杂形变转换为有限个离散形变单元组成的弹性形变,以分叉点、转折点、指纹图像上两点的连线所穿越的脊线数量等特征作为特征指标,求出采样指纹与标准指纹的模糊贴近度,并创造性地以此为相似性测度,构造总体刚度方程,进而迭代求解最佳位移,完成指纹图像配准。实验表明,该算法位移量的误差最小,用时为8.894 s,其有效降低了算法复杂度,提高了精度,同时也有效避免了指纹复杂多样的形变等因素对指纹配准算法精度的影响。     

梯度与曲率变形力相结合的图像配准方法——大形变非刚性图像配准

Active Demons算法是Demons算法的改进形式,其将形变配准视作扩散问题,利用牛顿作用力与反作用力思想,仅依靠梯度信息确定浮动图像的位移,在处理大形变配准问题时存在配准精度不高的弊病。将等照度线曲率作为一个控制形变的驱动力因素引入Active Demons扩散方程,建立了一个具有梯度与曲率双重驱动力相结合的非线性扩散模型（Active G&C model）,并在Active G&C模型应用于大形变图像配准的算法实现过程中加入多分辨率策略,以提高大形变图像的配准精度。实验结果表明,这一模型较经典的Active Demons算法具有更好的配准性能。     

基于计算机显微视觉的微动平台位移测量方法

针对微动平台微位移测量中传统传感器可测自由度单一、成本高等问题,提出了利用计算机显微视觉测量微动平台位移的方法。根据小孔成像原理建立微视觉成像模型,建立图像坐标系与微动平台坐标系之间的雅各比矩阵。将微视觉图像进行二值化、形态学处理,以消除图像中的噪声。最后提取图像中连通域,并通过连通域重心坐标位置变化计算微动平台输出位移。实验证明:所提方法便捷高效,能够在较短时间内获得良好的测量精度,可用于微动平台输出位移测量。     

基于非刚性配准的交互式医学图像序列分割

提出了一种新的交互式医学图像序列分割算法,该算法将非刚性配准技术和解剖先验知识相结合把图像分割问题转化为图像配准问题。首先采用Demons算法进行图像配准,用光流法计算瞬时位移,设计了一个新的停止准则使其能自适应地确定迭代次数,并将它在金字塔型的多尺度框架下实现。然后用配准得到的形变域对已精确分割的图像进行形变就能自动地获得未分割目标图像的分割结果。扩展上述过程就可实现整个图像序列分割。试验结果表明该算法用户干预少、分割速度快、分割结果准确。     

基于肝脏力模型的机器人辅助进针策略

针对机器人辅助穿刺手术中软组织形变引起的安全性和准确性问题,基于猪肝进针力模型,在分析猪肝组织结构和力学特性的基础上提出了机器人辅助进针策略.它主要包括两点:一是在穿刺针进入肝脏瞬间,机器人自动停止进针,待软组织松弛片刎后,再以减半速度继续进针,以尽可能减小软组织形变对穿刺精度的影响,提高手术准确性.二是在穿刺针进入肝...     

基于SURF的增强现实标识物跟踪注册

针对基于标识物的增强现实跟踪注册方法对复杂环境的适应能力和鲁棒性的不足,提出一种用SURF实现标识物跟踪注册的改进算法。用SURF对平面标识物的特征点进行检测与描述,采用K-means算法对检测出的标识物特征点集合进行聚类分析得到其聚类中心,结合对视频图像中标识物的阈值分割与连通域分析,以聚类中心构建标识物的SURF特征点坐标系,通过矩阵变换实现标识物的跟踪注册。实验结果表明,该算法的增强现实系统具备较好的鲁棒性、稳定性和实时性。     

针穿刺软组织变形有限元仿真

为了提高机器人辅助针穿刺精度,提出一种对软组织变形分析的准静态有限元法.该方法基于针受力下软组织变形机理,将软组织变形的连续动态过程分解成离散的准静态过程;采用重叠单元法在ANSYS中建立了软组织变形的二维和三维准静态有限元模型,并进行了仿真实验.最后通过实验结果验证了该方法的有效性和可行性.     

基于虚拟弹簧模型的柔性针穿刺仿真研究

在分析柔性针受力和挠曲的基础上,建立二维空间上柔性针穿刺软组织的虚拟弹簧模型,得到针体和针尖轨迹的数学模型。使用Matlab工具软件对针尖轨迹在不同情况下进行仿真。仿真实验结果表明,柔性针弹性变形量对针尖走向影响较小,影响针尖走向的主要因素是纵向控制坐标和针座与水平线初始夹角,且两者的叠加效应最终影响柔性针走向,可以为机器人辅助针穿刺操控提供理论基础,结合软组织变形研究,能够实现柔性针穿刺的轨迹规划和避障运动。     

Issues in closed-loop needle steering

Percutaneous needle insertion is amongst the most prevalent clinical procedures. The effectiveness of needle-base interventions heavily relies on needle targeting accuracy. However, the needle interacts with the surrounding tissue during insertion and deflects away from its intended trajectory. To overcome this problem, a significant research effort has been made towards developing robotic systems to automatically steer bevel-tipped needles percutaneously, which is a comprehensive and challenging control problem. A flexible needle inserted in soft tissue is an under-actuated system with nonholonomic constraints. Closed-loop feedback control of needle in tissue is challenging due to measurement errors, unmodelled dynamics created by tissue heterogeneity, and motion of targets within the tissue. In this paper, we review recent progress made in each of the complementary components that constitute a closed-loop needle steering system, including modelling needle-tissue interaction, sensing needle deflection, controlling needle trajectory, and hardware implementation.     

生物软组织力反馈触觉建模测试系统研制

设计了一种结构新颖的用于生物软组织力反馈触觉建模的测试系统。阐述了系统结构与工作原理,介绍了系统的机械设计、硬件电路和系统软件。系统采用计算机测量并控制带有力和位置传感器的单自由度机械手,通过插针实验与动物软组织交互得到软组织的力反馈触觉模型。以猪肝为标本进行实验,实验结果和现有的理论模型较为符合,该系统可以用于软组织触觉建模实验研究。     

Developing a method to plan robotic straight needle insertion using a probability-based assessment of puncture occurrence

Needle-based treatments for cancer require accurate placement of the needle tip into the target tissue. However, it is often difficult to insert a needle accurately because of the cancer displacement caused by organ deformation. Therefore, developing a planning method based on a numerical simulation that analyzes organ deformation is important for accurate needle insertion. However, predicting the puncture conditions, including the force applied to the needle is not trivial owing to marked variations in the experimental data. The purpose of this research is to develop a novel method for predicting a robust path for straight needle insertion with various puncture points. The method is based on the probabilities of the various puncture conditions and evaluates the expected accuracy of needle placement. First, a probability-based puncture condition was established and the expected accuracy of needle placement was defined. We also performed in vitro needle insertion experiments using a porcine liver. Significant variations in puncture force were observed. Accordingly, we established a probability distribution for the tissue stress caused by the puncture. An in vitro experiment was performed to measure needle placement accuracy using the optimized path. Experimental results show that the proposed method achieves a mean accuracy of 1.5?mm.     

基于图像序列拓扑关系的扎针机器人控制系统设计

由于当前扎针机器人定位参数存在误差,导致扎针成功率低,造成患者要忍受多次痛苦的问题,设计了一种扎针机器人控制系统。该系统由机械臂部分、上位机控制系统、高清激光图像采集系统、和信号传感器等部分组成,主要硬件部分选用DHT01型医用高清镜头、PCI8814图像采集卡、和性能更强的ATMEGA32L型单片机,保障采集图片的清晰度和对机械臂的控制精度。在图像序列处理算法上计算多帧图像的相似度,使用FAST算子提取图像的特征点,并基于关键帧优化图像序列的拓扑关系,实现目标位置的准确定位。实验结果表明,提出扎针机器人系统设计在3个轴向的偏差度平均值分别为0.0449、0.0383、和0.0387,趋近于理论上的中心位置,扎针一次成功率可以达到94.50%。     

Shape from shading based on needle map and cellular automata

This paper presents a method for computing depth from a single grayscale image in two steps. Firstly, surface normals are parallelly and gradually adjusted by a procedure which includes three constraints: the smooth constraint ensures the recovered normals are smooth and integrable, the intensity gradient constraint ensures the recovered normals are consistent with the image gradient field, and the intensity constraint guarantees the recovered intensity is equal to the input image. Unlike their usage in global methods, those constraints are separately used in local area in our method. Secondly, the surface is recovered from needle map using a two-dimensional cellular automata system. An experimental assessment is provided for our methods on both real world images and synthetic images with known ground truth. The experiment results demonstrate this approach is practicable and has better precision than traditional methods.     

Needle Insertion Parameter Optimization for Brachytherapy

This paper presents a new needle path planning method for the insertion of rigid needles into deformable tissue. The needle insertion point, needle heading, and needle depth are optimized by minimizing the distance between a rigid needle and a number of targets in the tissue. The optimization method is based on iterative simulations performed using a tissue finite element model. At each iteration, the best 3-D line fitted to the displaced targets in the deformed tissue is used as a candidate for a new insertion line. First, this method is implemented in a prostate brachytherapy simulator under different boundary conditions to minimize the targeting error. It is shown that the optimization method converges in a few iterations and decreases the seed misplacement error to less than the needle diameter. Second, the efficacy of the optimization algorithm is verified by optimizing the insertion parameters for a brachytherapy needle before insertion into a prostate tissue phantom. The elastic properties of the phantom and the needle-tissue interaction parameters were identified in an independent experiment. The optimization algorithm is effective in decreasing the targeting error.