Analysis of 2-D motion tracking in ultrasound with dual transducers

We study displacement and strain measurement error of dual transducers (two linear arrays, aligned orthogonally and coplanar). Displacements along the beam of each transducer are used to obtain measurements in two-dimensions. Simulations (5 MHz) and experiments (10 MHz) are compared to measurements with a single linear array, with and without angular compounding. Translation simulations demonstrate factors of 1.07 larger and 8.0 smaller biases in the axial and lateral directions respectively, for dual transducers compared to angular compounding. As the angle between dual transducers decreases from 90° to 40°, for 1% compression simulations, the lateral RMS error ranges from 2.1 to 3.9 μm compared to 9 μm with angular compounding. Simulation of dual transducer misalignment of 1 mm and 2° result in errors of less than 9 μm. Experiments demonstrate factors of 3.0 and 5.2 lower biases for dual transducers in the axial and lateral directions respectively compared to angular compounding.     

机抖激光惯导圆锥误差补偿算法研究

随着陀螺技术的发展,激光惯导陀螺数据输出频率变高,常用圆锥误差补偿算法使得系统运算负荷较大且无法有效挖掘高频数据对圆锥误差的补偿潜力。针对上述问题,提出五子样二次迭代圆锥误差补偿算法,推导了五子样二次迭代优化算法公式,并与双回路二子样、三子样优化算法进行了对比计算。经研究表明,该算法在保证惯导数据更新频率的同时有效提高了圆锥误差补偿效果,且相对于目前常用算法,对系统造成的运算负荷较小。提高了激光惯导系统在圆锥运动等恶劣工作环境下的工作性能。     

Dynamics of pedestrians in regions with no visibility— A lattice model without exclusion

We investigate the motion of pedestrians through obscure corridors where the lack of visibility (due to smoke, fog, darkness, etc.) hides the precise position of the exits. We focus our attention on a set of basic mechanisms, which we assume to be governing the dynamics at the individual level. Using a lattice model, we explore the effects of non-exclusion on the overall exit flux (evacuation rate). More precisely, we study the effect of the buddying threshold (of no-exclusion per site) on the dynamics of the crowd and investigate to which extent our model confirms the following pattern revealed by investigations on real emergencies: If the evacuees tend to cooperate and act altruistically, then their collective action tends to favor the occurrence of disasters. The research reported here opens many fundamental questions and should be seen therefore as a preliminary investigation of the very complex behavior of the people and their motion in dark regions.     

Human detection based on motion object extraction and head–shoulder feature

Aimed at the shortcomings of the traditional video monitoring system, human detection method in intelligent video monitoring system was researched. This paper proposed a human detection method based on motion object extraction and head–shoulder feature to complete human detection and statistics in video image sequences. Firstly, background subtraction based on adaptive threshold was used to extract foreground moving object information, then image erosion and image dilation were used to bypass the object shade and remove false object in order to optimize the results of motion object extraction. And finally, for realizing human moving object detection, we proposed the object discrimination algorithm based on human head–shoulder feature to complete human detection and statistics. Experimental results show that the method can successfully realize human detection and statistics. The method is highly accurate and has good real-time and extensive applications. The identification rate is 86% through human video sequences to test. This method can detect human automatically and provide the theoretical and technological base for object detection in the intelligent surveillance system.     

彩色大面阵航空测绘相机前向像移补偿分析及误差纠正

为了提高彩色大面阵航空测绘相机的成像分辨率和测绘精度,对其前向像移补偿的可行性进行了分析,并设计了前向像移补偿机构。根据航空成像的中心投影模型,研究了前向像移补偿下航空测绘相机内、外方位元素的变化对成像过程的影响,证明了前向像移补偿的可行性;设计了一套基于等径共轭凸轮机构的前向像移补偿机构,并分析了各种误差因素对测绘精度的影响;提出了基于仿射变换的误差纠正方法。实验结果表明,提出的前向像移补偿方法正确,机构引入误差的纠正精度可以达到0.001mm。     

Improvement of image quality using BLADE sequences in brain MR imaging

The purpose of this study is to compare two types of sequences in brain magnetic resonance (MR) examinations of uncooperative and cooperative patients. For each group of patients, the pairs of sequences that were compared were two T2-weighted (T2-W) fluid attenuated inversion recovery sequences with different k-space trajectories (conventional Cartesian and BLADE) and two T2-TSE weighted with different k-space trajectories (conventional Cartesian and BLADE). Twenty-three consecutive uncooperative patients and 44 cooperative patients, who routinely underwent brain MR imaging examination, participated in the study. Both qualitative and quantitative analyses were performed based on the signal-to-noise ratio, contrast-to-noise ratio (CNR), and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of motion, other (e.g., Gibbs, susceptibility artifacts, phase encoding from vessels) artifacts and pulsatile flow artifacts was evaluated.     

Motion predicted online dynamic MRI reconstruction from partially sampled k-space data

In this work we address the problem of reconstructing dynamic MRI sequences in an online fashion, i.e. reconstructing the current frame given that the previous frames have been already reconstructed. The reconstruction consists of a prediction and a correction step. The prediction step is based on an Auto-Regressive AR(1) model. Assuming that the prediction is good, the difference between the predicted frame and the actual frame (to be reconstructed) will be sparse. In the correction step, the difference between the predicted frame and the actual frame is estimated from partially sampled K-space data via a sparsity promoting least squares minimization problem. We have compared the proposed method with state-of-the-art methods in online dynamic MRI reconstruction. The experiments have been carried out on 2D and 3D Dynamic Contrast Enhanced (DCE) MRI datasets. Results show that our method yields the least reconstruction error.     

Coadjoint Orbits of Certain Motion Groups and Their Coherent States

Let ?_n, n ≥ 1, be the (2n+1)-dimensional Heisenberg group and let K be a closed connected subgroup of the unitary group U(n) acting on ?_n by automorphisms. Using the moment map, we provide in this paper a dequantization procedure for all generic admissible coadjoint orbits of the semidirect product G = K ? ?_n. In the opposite direction, we show that Gilmore-Perelomov's coherent states define “pure state quantizations” of such orbits.     

光电跟踪系统的共轴跟踪控制技术研究

为了提高光电跟踪系统的跟踪精度,对其粗跟踪环节的共轴跟踪控制技术进行了研究。介绍了共轴跟踪控制的基本原理,分析了常用非线性卡尔曼滤波算法,并仿真比较了无迹卡尔曼滤波(UKF)和容积卡尔曼滤波(CKF)的位置和速度的预测精度。在此基础上综合UKF和CKF的优点,设计了对延迟的合成位置信号进行处理的双并联滤波器,实现了光电跟踪系统的共轴跟踪控制。利用实测数据仿真实验表明,光电跟踪系统的跟踪精度明显提高。     

离子束治疗中的靶区运动补偿方法

相对于被动式束流配送系统,由患者呼吸因素而引起的肿瘤靶区运动会对主动式束流配送系统下的离子束放射治疗带来非常严重的影响,造成离子束辐射场剂量分布的严重畸变,甚至对肿瘤靶区周围的健康组织造成严重损伤,很大程度上影响离子束治疗的疗效。因此,在主动式束流配送系统下,建立针对由呼吸因素引起的运动肿瘤靶区的适形调强照射方法就显得必要,且具有重要意义。系统介绍了呼吸运动探测、4D-CT 以及目前主要的3 种运动补偿方法(多次扫描、呼吸门控和主动跟踪技术),并对这3 种方法在靶区适形度、稳健性以及技术复杂度等方面进行了比较。在靶区适形度方面主动跟踪技术优于门控技术,而门控技术又优于多次扫描技术;在稳健性方面多次扫描技术优于门控技术,而门控技术优于主动跟踪技术;在技术复杂度方面,多次扫描技术最简单,其次是门控技术,而主动跟踪技术最复杂。Active beam scanning results in serious distortion of ion-beam irradiation field in the presence of target motion and causes damage to healthy tissues round tumor target compared to passive beam shaping techniques. Therefore,it is necessary to establish suitable conformal irradiation methods for moving targets caused by the factor such as respiration in active ion beam scanning system. In this paper, motion detection, 4D-CT and three main ion beam specific mitigation techniques, namely rescanning, gating and beam tracking, are introduced. In addition, three motion mitigation techniques are compared comprehensively in terms of target conformation, robustness and mplementation complexity,respectively. For target conformation, the beam tracking is superior to gating, and gating is better than beam rescanning;the robustness decreases in the order rescanning-gating-beam tracking; for implementation complexity, beam rescanning is the most simple technology, followed by gating, while beam tracking is the most complex technique.