基于心磁信号的心脏电流偶极子阵列成像及相关性质的研究

超导量子干涉器（SQUID）能探测到微弱的心脏磁场信号. 通过对所得的心磁信号进行分析,可为许多心脏疾病的诊断提供依据. 利用心磁信号,采用极小范数最小二乘法（MNLS）对心脏的电流偶极子阵列进行重建,从而实现了对心脏内部等效电流源的成像. 在使用MNLS进行电流偶极子阵列反演重建的过程中,反演所需的心磁信号,分别由单电流偶极子和电流多极子作为激发源模拟得到,以及由SQUID实际测量得到. 同时,对不同心磁信号反演得到的电流偶极子的分布规律进行了分析. 此外,还给模拟的人体外心磁信号施加了均匀噪声和随机噪声,研究不同信噪比的均匀噪声和随机噪声对电流偶极子阵列重建的影响.     

串联超导量子干涉器件阵列制备与测试分析

串联超导量子干涉器件(superconducting quantum interference device,SQUID)阵列通过增加 SQUID 数量来达到提升信噪比的目的,即SQUID电压信号随SQUID数目比例增加而总电压噪声正比于SQUID数目的平方根值.本文介绍了利用自主工艺线进行串联SQUID阵列研究的相关研究进展,实现了SQUID数量分别为200和800的阵列集成,测试得到磁通噪声达到0.5 μΦ_0/Hz~(1/2)和输入电流灵敏度35 μA/Φ_0,等效输入电流噪声达到18 pA/Hz~(1/2).另外,还给出了阵列参数与集成SQUID数量的关系,验证了设计可靠性和工艺一致性.     

射频SQUID心磁图数据自适应滤波研究

研究了滤除50Hz工频干扰的几种自适应算法，并应用于射频超导量子干涉仪（SQUID）心 磁图仪采集的心磁数据50Hz滤波中.对算法的性能进行了计算机仿真比较.结果表明，带50 Hz干扰的SQUID心磁信号通过自适应噪声对消法，干扰得到了很好的抑制. 关键词： SQUID 心磁图 自适应滤波 噪声消除     

超导量子干涉器件

超导现象是一种宏观量子现象.磁通量子化和约瑟夫森效应是两个最能体现这种宏观量子特性的物理现象.超导量子干涉器件(superconducting quantum interference device,SQUID)是利用这两个特性而形成的超导器件.SQUID器件在磁信号灵敏探测方面具有广泛的应用.本文简要介绍低温超导和高温超导SQUID器件的相关背景和发展现状以及应用领域.     

多腔体心脏磁场模型的研究与应用

利用核磁共振图像(MRI)中提取的人体和心脏边界,根据边界元方法(BEM)建立了一个考虑左、右心房和心室的多腔体心脏磁场模型.分析了用该模型得到的36通道心脏磁场数据和特定时刻的磁场图.并在此基础上,研究了完全性右束支传导阻滞(CRBBB)和完全性左束支传导阻滞(CLBBB)病人ST-T段的心脏电活动.结果显示,用移动单电流偶极子模拟的单束支电兴奋传导所产生的磁场图与用超导量子干涉器(SQUID)测量的CRBBB/CLBBB病人数据绘制的心脏复极时的心磁图(MCG)十分相似.结果表明,该多腔体心脏BEM模型可用于CLBBB/CRBBB病人心脏磁场逆问题的研究.此外,文中给出了两个评价指标:测量平面上多腔体与单腔体的心脏磁场强度极大值之比,以及两种模型的36个测量点上磁场强度均方根之比.分析表明,多腔体心脏模型更贴近人体心脏的实际情况.该模型中心脏组织电导率参数的取值,以及等效电流偶极子的位置和个数决定了磁场的强度和分布.     

基于小波包分析的心磁信号消噪

心磁图(Magnetocardiography)是一种无创性记录和分析心脏电磁场的方法.由于心磁场强度极其弱小,必须使用超导量子干涉仪(SQUID)才能检测,其中心磁信号消噪处理十分重要.本文对心磁测量中的消噪进行了研究,在小波分析的基础上,提出使用小波包分析方法消噪,通过实验发现小波包分析消噪能获得很好的效果.     

航空超导全张量磁梯度仪的串扰研究

航空超导全张量磁梯度仪是使用飞行平台搭载的磁法测量设备,因其磁场灵敏度高、采集信息丰富、体积小等特点,被认为是第三代航磁探测的发展方向.本文构建了六棱锥构型的全张量梯度模块,由一个三轴超导量子干涉器(SQUID)磁强计和6个低温超导平面一阶SQUID梯度计组成.测试结果表明,在该多通道系统中,SQUID之间的串扰明显,对测量结果造成影响.本文对该超导全张量磁梯度仪的串扰进行了分析,并测量了串扰数据.分析了影响串扰的因素后,通过增加SQUID间的间距和改变接线方式等措施,对全张量模块结构进行了优化.实验结果表明,新构型模块对串扰改善在一个数量级以上,极大地提高了超导全张量磁梯度仪的精度和实用性.     

低温超导全张量磁梯度计不平衡度补偿研究

超导全张量磁梯度仪因其信息量丰富、磁场灵敏度高、体积小等特点,被认为是第三代航磁探测的发展方向.全张量梯度仪可由多个不共面的平面一阶超导量子干涉器件(SQUID)梯度计构成.目前,采用微纳加工工艺制备的超导平面梯度计能获得最好的平衡度,其共模抑制比可达103~104,但仍然不能满足运动条件下的应用需求.在实际应用中,可采用三轴SQUID磁强计对梯度计进行补偿,达到抑制运动噪声的目的.本文基于最小二乘(LMS)自适应滤波算法,通过数值仿真分析了平面梯度计的不平衡度、环境磁场大小以及环境剩余磁梯度对补偿效果的影响.同时,我们构建了六棱锥构型的全张量超导梯度仪,并采用三轴磁强计作为补偿通道,在野外均匀地球磁场下进行了测试.结果表明,该补偿方法能够大幅减小均匀磁场下的梯度计的不平衡输出,可以将梯度值补偿约2个数量级,极大提高了超导全张量磁梯度仪在运动状态下的实用性.     

在SQUID心磁测量中基于奇异值分解和自适应滤波的噪声消除法

采用矩阵奇异值分解(singular value decomposition, SVD)的方法，对高温射频超导量子干涉仪(HTc rf-SQUID)采集到的单通道心磁信号进行处理.证明了对于近似周期性的心磁信号，在无参考噪声的情况下矩阵奇异值分解的方法与自适应窄带陷波相结合有较好的消除广谱噪声的效果. 关键词： 高温射频超导量子干涉仪 心磁信号 奇异值分解 噪声消除     

HT_c rf SQUID用于磁异常移动测量的初步研究

高温超导量子干涉器(HTcSQUID)磁强计的基本特点是噪声低、低频响应好、工作带宽大,在需要微弱磁场测量的许多技术领域发挥着重要作用,将其用于磁异常探测(MAD)是搜索地下/水下磁性目标物的有效技术。本文采用国产射频高温超导量子干涉器(HTcrf SQUID)磁强计,在非磁屏蔽环境中开展了移动状态下的磁异常探测实验,初步结果表明,基于HTcrf SQUID磁强计的MAD技术是一项具有研究和使用价值的新技术。     

Cardiac magnetic source imaging based on current multipole model

It is widely accepted that the heart current source can be reduced into a current multipole. By adopting three linear inverse methods, the cardiac magnetic imaging is achieved in this article based on the current multipole model expanded to the first order terms. This magnetic imaging is realized in a reconstruction plane in the centre of human heart, where the current dipole array is employed to represent realistic cardiac current distribution. The current multipole as testing source generates magnetic fields in the measuring plane, serving as inputs of cardiac magnetic inverse problem. In the heart-torso model constructed by boundary element method, the current multipole magnetic field distribution is compared with that in the homogeneous infinite space, and also with the single current dipole magnetic field distribution. Then the minimum-norm least-squares (MNLS) method, the optimal weighted pseudoinverse method (OWPIM), and the optimal constrained linear inverse method (OCLIM) are selected as the algorithms for inverse computation based on current multipole model innovatively, and the imaging effects of these three inverse methods are compared. Besides, two reconstructing parameters, residual and mean residual, are also discussed, and their trends under MNLS, OWPIM and OCLIM each as a function of SNR are obtained and compared.     

The forward and inverse problem of cardiac magnetic fields based on concentric ellipsoid torso-heart model

<正>This paper constructs a concentric ellipsoid torso-heart model by boundary element method and investigates the impacts of model structures on the cardiac magnetic fields generated by both equivalent primary source—a current dipole and volume currents.Then by using the simulated magnetic fields based on the torso-heart model as input,the cardiac current sources—an array of current dipoles by optimal constrained linear inverse method are constructed.Next, the current dipole array reconstruction considering boundaries are compared with that in an unbounded homogeneous medium.Furthermore,the influence of random noise on reconstruction is also considered and the reconstructing effect is judged by several reconstructing parameters.     

基于贪婪稀疏方法的心脏磁场源重构

心脏磁场源重构, 即通过人体胸腔表面的磁场阵列测量信号反演产生该磁场的电流源分布, 是一种无创地研究心脏电活动的方法. 本文用线性化方程描述测量磁场与心脏内部电流源的关系, 并通过一种贪婪优化的方法得到了源重构的稀疏解. 通过近似正交化过程和改变迭代算法中原子的选择方式, 降低了优化算法的复杂度, 可在保证源重构精度的情况下, 快速搜索源空间中强度比较大的位置. 文中通过一组正常人的心磁测量数据, 说明了源重构方法的有效性. 这组数据的研究结果表明, 强度大于65%的重构电流源的空间移动轨迹与心脏除极和复极电活动的传导过程基本符合. 其QRS 和ST-T 段的实测心磁图与重构电流源产生的磁场图的平均拟合优度分别为99.36%和99.78%. 关键词： 心磁图 逆问题 稀疏解 正交匹配追踪     

Forward and inverse problem for cardiac magnetic field and electric potential using two boundary element methods

This paper discusses the forward and inverse problem for cardiac magnetic fields and electric potentials.A torso-heart model established by boundary element method(BEM) is used for studying the distributions of cardiac magnetic fields and electric potentials.Because node-to-node and triangle-to-triangle BEM can lead to discrepant field distributions,their properties and influences are compared.Then based on constructed torso-heart model and supposed current source functional model-current dipole array,the magnetic and electric imaging by optimal constrained linear inverse method are applied at the same time.Through figure and reconstructing parameter comparison,though the magnetic current dipole array imaging possesses better reconstructing effect,however node-to-node BEM and triangleto-triangle BEM make little difference to magnetic and electric imaging.     

Inverse computation for cardiac sources using single current dipole and current multipole models

Two cardiac functional models are constructed in this paper. One is a single current model and the other is a current multipole model. Parameters denoting the properties of these two models are calculated by a least-square fit to the measurements using a simulated annealing algorithm. The measured signals are detected at 36 observation nodes by a superconducting quantum interference device (SQUID). By studying the trends of position, orientation and magnitude of the single current dipole model and the current multipole model in the QRS complex during one time span and comparing the reconstructed magnetocardiography (MCG) of these two cardiac models, we find that the current multipole model is a more appropriate model to represent cardiac electrophysiological activity.     

用于心脏电活动成像的空间滤波器输出噪声抑制方法

利用人体表面测量的心脏磁场数据无创成像心脏电活动,需要解决的关键问题是提高其重建分布电流源偶极矩强度的分辨率.本文在最小方差波束成形(MVB)方法的基础上,提出了一种可抑制空间滤波器输出噪声功率增益(SONG)的波束成形方法,目的是通过构造一种新的滤波器权矩阵,约束空间滤波器的输出噪声功率增益,提高重建分布电流源偶极矩强度的分辨率,即分布电流源空间谱估计的源分辨能力,从而增强心脏电活动磁成像的分辨率.文中给出了电流源重建的理论分析和仿真结果;比较了该方法与MVB方法的差别;并给出了两个健康人36通道心脏磁场数据的电活动成像.结果表明,SONG方法分辨电流源的能力较强,能够观察到心脏电磁场信号R峰时刻健康人的心室电活动较强,心房电活动较弱等特征.     

具有Washer型输入线圈的超导量子干涉放大器的制备与表征

超导量子干涉仪(SQUID)放大器具有低输入阻抗、低噪声、低功耗等优点, 目前被广泛用于微弱信号的检测领域. 与其他工艺相比, Nb/Al-AlO_x/Nb结构的约瑟夫森结具有相对较高的转变温度(T_c)、高的磁通电压调制系数以及良好的热循环能力、较宽的临界电流范围, 因此是制备SQUID放大器的很好选择. 设计并制作了欠阻尼、过阻尼约瑟夫森结以及具有Washer型输入线圈的单SQUID放大器, 通过在He³制冷机3 K温区下对器件电流-电压特性进行测量, 得到良好的结I-V特性曲线、SQUID调制特性, 初步实现利用SQUID进行放大作用, 并计算了SQUID的电流分辨率. 此项工作对于超导转变边沿传感器读出电路的实现具有重要的意义.     

Measurements, characteristics, and origin of new electromagnetic interference on magnetocardiographic measurements

In order to eliminate the influence of the large-amplitude magnetic field noise that has complicated magnetocardio-graphic studies since October 2009, we have performed high-accuracy measurement of the environmental magnetic field noise in the vicinity of Beijing Subway Line 4 using a three-component height T c radio frequency (rf) superconducting quantum interference device (SQUID). By analysing the spatial form and other characteristics of the time and the frequency domains and by calculating the circumferential magnetic field distribution based on a duel-end feeding system model, we reach the following conclusions: (i) the main source of magnetic field noise is the magnetic field generated by the subway trains, and (ii) the magnetic field interference results mainly from the imbalance between traction current and return rail current that is caused by the leakage current.