Data analysis for dynamic contrast-enhanced MRI-based cerebral perfusion measurements: correcting for changing cortical CSF volumes

The time evolution of the histogram (number of pixels versus signal intensity) is used to calculate ΔR ₂ parameters from dynamic contrast-enhanced magnetic resonance (MR) imaging of the brain. This method partially corrects for partial volume effects and is an improvement over the approach using the signal intensity as a function of time when confounding factors such as changing cortical cerebrospinal fluid volumes are involved. The maximum value for ΔR ₂ is found to correlate with relative cerebral blood flow as assessed by xenon inhalation and can be used to discriminate between vascular dementia and healthy volunteers. With this method, the normal range for ΔR ₂ values is found to be the same for both young (19–40 years old) and elderly (65–85 years old) healthy volunteers.     

Signal injection method without torque ripple based on maximum torque control frame

This paper presents a new signal injection method without torque ripple for sensorless controls of salient‐pole synchronous motors at low speeds. At low speeds, since the back electromotive force (EMF) including position information decreases, additional signals are injected to estimate position information of saliency. The torque ripple caused by the injections of signal currents can be represented by a cross product of a virtual flux and a differential current vector. An f‐axis of maximum torque control frame is defined to the direction of the virtual flux. Therefore, signal injection without torque ripple is realized by using the f‐axis current. In this paper, a signal injection method with f‐axis current is proposed, and the effects of the estimation error are discussed to apply the method for position‐sensor‐less controls. The proposed injection method allows us to flexibly design frequencies of the signal current. The validity of the proposed method and applicability to position estimation are confirmed by experimental tests. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于超声波方法的管内气固两相流浓度测量技术

对一种基于超声波被动接收原理的管内气固两相流浓度测量方法进行了研究。在煤粉的弯头外侧装设超声波接收器，通过接收气固两相流内固体颗粒撞击弯头管壁产生的超声波信号，经过增益器将信号传送到计算机，计算机对超声波信号处理后，根据不同固体浓度下信号特征的变化获得管内气固两相流的浓度。试验结果表明，该方法可实现气固两相流中固体浓度的连续在线测量，采用方均根电压作为超声信号的分析具有最佳的分辨率。     

Small‐signal analysis of interleaved dual boost converter

This paper presents a systematic development of steady‐state, small‐signal models of interleaved dual boost converter operating in a continuous current mode. These models are derived by employing the well‐known signal flow graph method. This signal flow graph approach provides a means to directly translate the switching converter into its equivalent graphic model, from which a complete behaviour of the converter can easily be studied. Steady‐state performance, small‐signal characteristic transfer functions are derived using Mason's gain formula. The bode plots of audiosusceptibility, input impedance, output impedance, and control‐to‐output transfer functions are determined and illustrated using MATLAB for different values of load resistances, duty ratios. Small‐signal frequency responses obtained from the signal flow graph method are validated with PSPICE simulator results. To validate the signal flow graph modelling equations, sample steady‐state experimental results are provided. Copyright © 2001 John Wiley & Sons, Ltd.     

Comparison of breath-hold 2D phase-contrast with non breath-hold cine phase-contrast MRA in the assessment of azygos venous blood flow in portal hypertension

Azygos venous blood flow as an index of blood flow through the gastroesophageal collaterals and varices is of value in the prediction of gastrointestinal bleeding. Measurement of azygos venous blood flow has been achieved by non breath-hold (NBH) cine phase-contrast magnetic resonance imaging. The objective of this study was to compare the faster breath-hold (BH) phase-contrast technique with the standard (NBH) cine phase-contrast technique in the measurement of azygos blood flow. Thirty-two cirrhotic patients with esophageal varices were examined by magnetic resonance imaging using a BH technique and a NBH cine phase-contrast technique to measure the flow velocity, flow volume and calibre of the azygos vein at the mid-right atrial level. The flow values were obtained on the velocity image of the phase-contrast study. Values obtained from the two methods were evaluated statistically for the strength and significance of correlation by the Pearson test. Measurement by the BH method performed at full-inspiration as well as end-expiration was also obtained in 15 healthy volunteers. The breath-hold phase-contrast method has significant but weak correlation with non BH cine phase-contrast method in the measurement of azygos venous blood flow volume (r=0.55, p<0.01) and flow velocity (r=0.43, p=0.01). However, the calibre of the azygos vein gave a strong correlation in these two methods (0.82). In the subgroup of patients whose azygos blood flow velocity was greater than 7.4 cm/s, the correlation of azygos blood flow volume is strong (r=0.80, p<0.01). The azygos vein calibre remains highly correlated between the BH and NBH method, in both high flow velocity (r=0.73) and low flow velocity (r=0.83) groups. Breath-hold sequence leads to higher values for flow velocity and flow volume in the cirrhotic patients and also the control group. In patients with portal hypertension, BH 2D phase-contrast (PC) magnetic resonance angiography (MRA) could give a comparable estimation of the calibre of the azygos vein as the NBH 2D cine PC MRA but not for azygos flow volume. In patients with high azygos flow velocity, the strong correlation in flow volume between the BH and NBH method suggests that the BH method may be a time-saving alternative to the NBH method.     

规则法和混合法相结合的遥信错误辨识方法

针对遥信错误辨识问题,提出了一种基于规则和混合法的遥信错误辨识方法。首先制定规则剔除简单的遥信错误;对于无法通过简单规则辨识的遥信,提出采用转移潮流法和新息图法相结合的拓扑错误混合辨识方法进行辨识,该混合辨识方法具有如下特点:以前一断面的状态估计结果作为基态,避免转移潮流法在实际工程中基态选择的困难;通过新息图法中的修正预估比判断拓扑可疑支路,避免转移潮流法中用转移潮流判定拓扑可疑支路可能导致的误判;引入转移潮流法中注入功率对转移潮流的影响量,避免采用新息图法出现较大负荷预测误差产生负荷突变问题。最后,以算例证明了所述方法的有效性。     

Ultra-fast three dimensional imaging of hyperpolarized 13C in vivo

Objective: PASADENA, a chemical method of enhancing nuclear spin polarization has demonstrated ¹³C polarizations of order unity for the nascent products of molecular addition by parahydrogen. The extreme brevity of signal enhancement obtained by hyperpolarization requires improved ¹³C MR in vivo imaging techniques for their optimum utility. Materials and Methods: ¹³C imaging sequences, including ¹³C 3D FIESTA, were compiled for a GE LX 1.5 T clinical MR scanner. Two water soluble ¹³C imaging agents were hyperpolarized utilizing parahydrogen and an automated polarizer. ¹³C polarization was quantified in flow phantoms and in rats with jugular vein catheters. Results: Fast 3D FIESTA ¹³C MR imaging technique acquired sequential 3D images (3.66 s/acquisition) with superior SNR. Hyperpolarized ¹³C solutions and vascular phantoms achieved a maximum signal of 26,624±593. In vivo ¹³C MR images of the cardiopulmonary circulation showed maximum ¹³C signal of 2,402±158. ¹³C images acquired within 3.66 s showed signal enhancement over 10,000 compared to equilibrium polarization. Conclusion: 3D-FIESTA was effective for sub-second in vivo imaging of hyperpolarized ¹³C reagents produced in a custom-built parahydrogen polarizer. Application to ¹³C hyperpolarized by parahydrogen is demonstrated in vitro and in vivo     

基于坐标旋转变换的配电系统快速解耦潮流计算方法

配电系统中各支路的电阻与其电抗的比值较大,因此,经典的快速解耦潮流计算方法不适用于配电系统潮流计算。提出了一种坐标旋转变换方法,并将这种变换方法与经典的隐式Zbus高斯方法相结合,导出了配电系统的解耦潮流计算方法。以IEEE 33节点、IEEE 69节点和一个实际的145节点配电系统为例,对提出的解耦潮流算法进行了测试。结果表明,所提出的解耦方法不影响经典的隐式Zbus高斯方法的收敛性,因而是一种高效、实用的快速潮流计算方法。     

Hybrid-type stability control method based on combination of conventional PSS and fuzzy control

This paper presents a hybrid-type stability control method based on fuzzy control to improve power system stability. The proposed method consists of a speed deviation input fuzzy controller (F1), an electrical power deviation input analog-type PSS (ΔP-type PSS), and a fuzzy judgment mechanism (F2). By using the membership function of the magnitude of speed deviation/acceleration of the generator, the following control schemes are considered. If the magnitude is large, then the supplementary stabilizing signal computed by F1 is used to damp oscillations as fast as possible. Otherwise, the output signal of ΔP-type PSS is used to avoid undesirable noise effect due to noisy input signal of the speed deviation of F1. The proposed control method increases the power system stability greatly, and it is simple to implement. The effectiveness of the method is demonstrated by one-machine infinite-bus and multi-machine model systems.     

Relaxation for online frequency estimator of bias‐affected damped sinusoidal signals based on Dynamic Regressor Extension and Mixing

This paper considers the problem of continuous‐time online frequency estimation for a biased damped sinusoidal signal. The previous result for a sinusoidal signal with time‐varying amplitude requires a persistency of excitation condition for regressor, which is not satisfied in the considered case. To relax this condition, we propose to use Dynamic Regressor Extension and Mixing method on the first step to replace nth‐order regression with n first‐order regression models. On the second step, two simple relaxation methods are proposed to establish necessary excitation for the first‐order gradient‐based estimator. The efficiency of the proposed approach is demonstrated through the set of numerical simulations for the exponentially damped sinusoidal signal.     

Semiautomatic Analysis of Phase Contrast Magnetic Resonance Imaging of Cerebrospinal Fluid Flow through the Aqueduct of Sylvius

Objective: Quantification of the cerebrospinal fluid (CSF) flow through the aqueduct of Sylvius by means of magnetic resonance imaging (MRI) is subject to interobserver variability due to the region of interest (ROI) selection. Our objective is to develop a semiautomatic measurement method to achieve reproducible quantitative analysis of CSF flow rate and stroke volume. Material and methods: MR examinations were performed using a 1.5 T scanner with a phase contrast sequence (velocity encoding [V _enc] of 20 cm/s, FOV = 160, 3 mm slice thickness, image matrix size = 256×256, TR = 53 ms, TE = 11 ms, NSA = 2, flip angle = 15° and 23 frames per cardiac cycle with peripheral retrospective pulse gating). Our method was developed using MATLAB R7. Errors introduced by background offset and possible aliased pixels were automatically detected and corrected if necessary in order to calculate the flow parameters that characterize CSF dynamics. The semiautomatic seed method reproducibility was evaluated and compared with the radius method by two observers analysing 21 healthy subjects. Results: The measurements using the semiautomatic seed method reduced the interobservers variability (intra-class correlation [ICC] = 1.0 for stroke volume and for volumetric flow rate) versus the radius method (ICC = 0.46 for stroke volume and 0.65 for flow rate). Normal stroke volume (39.19 ± 20.13 μl/cycle), flow rate (3.81 ± 2.81 ml/min), maximal mean systolic velocity (5.27 ± 1.3 cm/s) and maximal mean diastolic velocity (4.20 ± 1.4 cm/s) were calculated with the half moon and aliasing corrected seed method. Conclusions: Semiautomatic measurements (seed method with half moon background and aliasing correction) allow a generalization of the calculus of flow parameters with great consistency and independency of the operator.     

A new formulation and solution method for the maximum loading point in electrical power systems

This paper proposes a new efficient formulation and solution method for a maximum loading point or saddle node bifurcation point in electrical power systems. This point, corresponding to a tip of the P(Q)-V curve, is characterized by singularity of the load flow Jacobian. The proposed formulation is of dimension n + 1, instead of 2n + 1 in the standard formulation, for n-dimensional load flow equations. The proposed method uses a 1-dimensional singularity condition, obtained from a reduction of the standard n + 1-dimensional singularity conditions. For this reduction, one of the diagonal elements of the load flow Jacobian is selected. We also propose an index for this selection to make the proposed method reliable. The solution for the proposed formulation can effectively be obtained based on the Newton-Raphson method with sparse matrix techniques. The computational performance of the proposed method is demonstrated on 6, 14, and 118 bus test systems. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(1): 17–25, 1997     

基于功率潮流分析的电能计量新方法

针对非平稳畸变信号条件下电能准确合理计量问题,在非线性负载泛函级数模型的基础上,进行了功率潮流分析并提出畸变信号条件下电能计量新方法。根据泛函级数理论中Wiener核与Volterra核转换定理求得负载的Volterra核,应用Volterra级数理论将正弦输入信号条件下负载输出电流与电压用Volterra泛函级数表示。利用小波分解与重构算法对电流与电压信号进行分解与重构,求出功率潮流分析所需电流与电压的基波分量与畸变分量。结合IEEE-Std1459-2010标准定义,以半导体整流器、电力机车及两者组成的复合系统为例,对非线性负载进行功率潮流分析,依据各功率潮流的物理意义及潮流方向,提出畸变信号条件下电能计量新方法。仿真结果表明非线性负载功率潮流仿真结果与理论结果一致,基于功率潮流分析的电能计量新方法能够实现畸变信号条件下电能的合理计量。     

A new pulse sequence to visualize slow flow

The purpose of this paper is to present a new pulse sequence for visualizing slow flow. The new sequence consists of an initial Stejskal–Tanner flow sensitization part followed by a DEFT pulse and a spoiler gradient. A single-shot TSE readout train is then applied to sample the NMR signal. The sequence was initially tested using a simple flow phantom. To verify potential clinical use, both flow-sensitive MRCP and cerebrospinal fluid (CSF) images were produced. The phantom study proved the sequence sensitivity to flow in the range 0–1 cm/s. b_VE-factors 1.5, 3, 6 and 12 were chosen. Within this flow velocity range, the signal dropped as predicted theoretically. This indicates that the method can be used to quantify flow. All anatomical features seen in a standard MRCP sequence were identified and the methods sensitivity to CSF flow was demonstrated by sagital images of the head. A new pulse sequence sensitive to slow flow has been developed.     

基于稀疏表示的TQWT在低频振荡信号去噪中应用

为了改善低频振荡信号的去噪效果,为低频振荡信号的检测与分析提供准确可靠的数据,在分析可调Q小波变换和稀疏表示原理的基础上,给出了一种基于稀疏表示的可调Q小波变换去噪方法。该方法先利用可调Q小波变换对含噪的低频振荡信号进行稀疏分解,得到初始的小波系数。再利用基追踪去噪算法对得到的小波系数进行优化处理。最后对优化的小波系数进行重构,获取干净无噪的低频振荡信号。通过仿真分析验证了该方法的去噪效果和可靠性优于目前广泛使用的小波软、硬阈值去噪法。     

Multi‐component instantaneous frequency estimation using locally adaptive directional time frequency distributions

This paper presents a locally adaptive time‐frequency (t,f) method for estimating the instantaneous frequency (IF) of multi‐component signals. A high‐resolution adaptive directional time‐frequency distribution (ADTFD) is defined by locally adapting the direction of its smoothing kernel at each (t,f) point based on the direction of the energy distribution in the (t,f) domain. The IF of signal components is then estimated from the ADTFD using an image processing algorithm. Using the mean square error between the original IF and estimated IF as a performance criterion, experimental results indicate that the ADTFD gives better IF estimation performance compared with other TFDs for a multi‐component signal. For example, for signal‐to‐noise ratio of 12dB, the IF estimate obtained using the ADTFD achieves a mean square error of ?42dB for a weak signal component, which is an improvement of ?12dB compared with other TFDs. Copyright © 2015 John Wiley & Sons, Ltd.     

基于双阈值比较法超声波流量计信号处理

选择时差法超声波流量计为研究对象,以其包络超声波信号为基础研究信号处理方法,进一步提高时差法超声波流量计的测量精准度和稳定度。针对超声波流量计信号的特点,提出了双阈值法,利用此方法进行信号畸形与否的判断,再在良好的信号基础上进行流速流量计算。利用双阈值进行5个时间点的采集,同时采集过高阈值的脉冲个数,通过这些条件进行信号判断,满足指定条件的将再此基础上,按照指定的标准进行流速流量计算。实验验证证明该方法提高了流量计的测量精度和稳定度。     

Complex diffusion process for noise reduction

Signal de-noising and restoration is an essential step for many signal processing algorithms and applications. One of the most common problems is the removal of some interesting structures in the signal during the restoration process. The capability of methods based on partial differential equations (PDEs) in image restoration and de-noising prompted many researchers to search for an improvement in the technique. In this paper, a new method is presented for signal de-noising, based on PDEs and Schrodinger equations, named as complex diffusion process (CDP). This method assumes that variations on signals are like geometric heat flow, in which heat transfers from a warm environment to a cooler one, until temperatures of the two environments are balanced. In this model, sudden variations in a signal not explained by PDEs are considered as noise. Results of our study show that CDPs are very suitable for signal de-noising. To evaluate the performance of the proposed method, a number of experiments have been performed using Sinusoid, multi-component and FM signals cluttered with noise. The results indicate that the proposed method outperforms the approaches for signal de-noising known in prior art.     

Digital filter design with state space method for 1‐bit signal processing based on delta‐sigma modulation

One‐bit signal processing based on delta‐sigma modulation has been studied for hardware implementation of signal processing systems. In the 1‐bit signal processing, finite word‐length problems such as overflow and coefficient quantization error occur. To solve the problems, a new design method with state space is proposed in this paper. Digital filters are designed to show the feasibility of the method. First, the L₁/L₂‐sensitivity is shown to evaluate coefficient quantization error and L₂ scaling constraints to prevent overflow. Second, a state space equation is presented and the L₁/L₂‐sensitivity and L₂‐scaling constraints are extended to take the filter structure and oversampling effects into account. Finally, the proposed method is shown to attain a higher SNR than conventional ones. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 48–56, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21075     

基于气体超声波流量计的间歇激励和信号处理

为了提高气体超声波流量计系统的响应速度,提出一种新的基于相邻峰值最大差值的气体超声流量计信号处理方法。为了进一步提高该信号处理方法的测量精度,又提出一种新的间歇式激励方法。采用间歇式激励方法能得到相邻峰值差值较大的回波信号,并且在不同流量下,相邻峰值最大差值的相对位置始终保持不变。在实际测量中,通过回波信号中相邻峰值最大差值的位置,确定回波信号的到达时刻,进而计算出超声波传播时间,得到气体流量。将间歇式激励方法和基于相邻峰值最大差值的信号处理方法在硬件系统上进行实时实现,并进行标定实验,结果验证了激励方法配合信号处理方法的高效性。