基于磁敏感的磁兼容金属植入物的正对比磁共振成像

在磁共振成像中,磁共振兼容金属植入物的磁化率较高,从而导致图像信号的缺失与失真,严重影响装置的精准定位和评估。2014年,有学者提出一种正对比成像方法,利用偏移180°回聚脉冲的自旋回波序列,结合特有的定量磁化率重建算法,重建出近距离放射颗粒的正对比图像。在此基础上,文章对该方法进行进一步扩展,在西门子3 T人体磁共振成像系统上,将该方法应用到活检针和过滤器等较大金属介入装置的正对比成像。活检针和过滤器水模磁共振成像实验结果表明,这种正对比成像方法可应用于较大的金属装置,有效地抑制了金属伪影,获得清晰的正对比图像,提高了装置定位和评估的精准度。     

基于归一化割的颅脑MRI肿瘤提取算法

颅脑核磁共振图像( MRI)的肿瘤图像由于自身对比度较低、肿瘤边缘模糊以及肿瘤形状复杂等因素,导致其难以被准确提取。为此,提出将归一化割算法和基于符号压力( SPF)函数的活动轮廓模型相结合,对颅脑MRI肿瘤进行提取的算法。利用基于SPF函数的活动轮廓模型,实现对归一化割算法提取肿瘤边缘的收敛,通过设置收敛的迭代次数和光滑系数完成对颅脑MRI肿瘤边缘的收敛速度和形状的控制,使最终曲线停止于真正的肿瘤边缘。仿真结果表明,该算法克服了肿瘤形状变化及对比度等因素对肿瘤提取的不利影响,能稳定而准确地提取颅脑MRI肿瘤。     

自跟踪信号的传递及提取

自跟踪信号的传递及提取的方式为三通道－双通道－单通道,目前采用的两个单通道合成方式较为先进,反映了自跟踪传递解调技术的发展历程,着重介绍了不同传递解调方式的工作原理、设备组成,并分析其优缺点。     

基于BP神经网络的MRI分割

本文提出了基于ＢＰ神经网络的脑部多回波磁共振图像分割方法。输入图像包括Ｔ１,Ｔ２,ＰＤ三种加权特征图像,分割是基于各像素点灰度值进行的。首先通过一组已标号的训练样本训练神经网络分类器,不正确的分割结果通过交互方式修正训练点,然后再次训练,直至满意的分割结果。     

含氢硅油中活性氢的测定

以苯为内标物，采用核磁共振（1HNMR）法，根据可测试的氢质子峰的积分面积，计算出含氢硅油中活性氢的质量分数，该方法所需样品量为60－80mg，分析时间为15min，具有简单，省时，准确等特点。     

基于FPGA的数字超声内窥镜接收系统设计

根据数字超声成像的要求和超声信号的特点,设计了由高速采样电路和FPGA正交解调电路组成的数字超声内窥镜接收系统。采样电路由AD8138和AD9235实现,对放大后的超声回波信号直接进行模数转换;FPGA利用内部RAM、乘法器、IP核和宏模块构建数字正交解调电路,提取超声回波信号的幅度;获取的幅度信息经USB2.0接口电路送入计算机显示。对玻璃杯进行的静止扫描成像实验,验证了接收系统的小信号检测能力,可以检测到信噪比约为4dB的回波信号;对玻璃杯进行的旋转扫描成像实验,表明接收系统可用于数字超声内窥镜成像。     

Damage prevention design of the branch pipe under pressure pulsation transmitted from main steam header

Vibration has severely increased at the branch pipe of the main steam header since the beginning of commercial operation of nuclear power plants. Intense broadband disturbance flow at a discontinuous region such as elbows, valves or headers generates an acoustical pulsation which is propagated through the piping system. The pulsation becomes the source of low frequency vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation related to high dynamic stress, and ultimately, to failure probability fatally affects the reliability and confidence of the plant piping system. This paper discusses steady-state high vibrations appearing in the branch piping system due to the effect of acoustical pulsations transmitted from the large main steam header by broadband turbulence in a 700 MW power plant. The excitation sources and response of the piping system are investigated by using on-site measurements and analytical approaches. Energy absorbing restraints with additional stiffness and damping factor were designed and installed to reduce vibration damage.     

Detection in near-field domain of biomolecules adsorbed on a single metallic nanoparticle

In this study, neurodegeneration phenomena were investigated, by performing third harmonic generation imaging measurements on the nematode Caenorhabditis elegans, in vivo. The in vivo, precise identification of the contour of the degenerating neurons in the posterior part of the nematode and the monitoring, in real time, of the progression of degeneration in the worm, through third harmonic generation imaging measurements, were achieved. Femtosecond laser pulses (1028 nm) were utilized for excitation. Thus, the THG image contrast modality comprises a powerful diagnostic tool, providing valuable information and offering new insights into morphological changes and complex developmental processes in live biological specimens.     

Combination Resonance Instability of Curved Panels with Cutout Subjected to Nonuniform Loading with Damping

The dynamic instability of doubly curved panels with a centrally located circular cutout, subjected to nonuniform compressive in-plane harmonic edge loading is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to single (mode) resonances in parametrically excited doubly curved panels with a central circular cutout. The method of multiple scales is used to obtain analytical expressions for the single (mode) and combination resonance instability regions. It is shown that other cases of the combination resonance can be of major importance and yield a significantly enlarged instability region in comparison to the principal instability region. The effects of nonuniform edge loading, centrally located circular cutout, damping, the static, and dynamic load factors on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as single (mode) resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which doubly curved panels cannot become dynamically unstable. A central circular cutout has the destabilizing effect on the dynamic stability behavior of doubly curved panels subjected to nonuniform edge loading. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.     

Dynamic Stiffness of Foundations on Inhomogeneous Soils for a Realistic Prediction of Vertical Building Resonance

The aim of this contribution is a practice-oriented prediction of environmental building vibrations. A Green’s functions method for layered soils is used to build the dynamic stiffness matrix of the soil area that is covered by the foundation. A simple building model is proposed by adding a building mass to the dynamic stiffness of the soil. The vertical soil-building transfer functions with building-soil resonances are calculated and compared with a number of measurements of technically induced vibrations of residential buildings. In a parametrical study, realistic foundation geometries are modeled and the influence of incompressible soil, deep stiff soil layering, soft top layers, and increasing soil stiffness with depth is analyzed. All these special soil models reduce the resonant frequency compared to a standard homogeneous soil. A physically motivated model of a naturally sedimented soil has a stiffness increasing with the square root of the depth and yields a foundation stiffness that decreases with foundation area considerably stronger than the relatively insensitive homogeneous soil. This soil model is suited for the Berlin measuring sites and reproduces satisfactorily the experimental results.