A multicoil array designed for cardiac SMASH imaging

Recently, several partially parallel acquisition (PPA) techniques have been presented which use spatial information inherent in an RF coil array to reconstruct an image from a reduced set of phase encoding steps. PPAs represent a change in paradigm for the RF coil designer since the focus for arrays to be used with PPAs is to optimize the spatial encoding that is provided by the array. One of the first practical implementations of PPA imaging was demonstrated using the SMASH technique. In this study, we present our results from the construction of the first array designed specifically for cardiac SMASH imaging. Additional design criteria are presented for SMASH arrays that are not considered in conventional array design. Using these design criteria, a four-element array was constructed and then tested in SMASH imaging experiments in the heart. This array has been used in all of our initial cardiac and head SMASH studies with good results.     

Moment method analysis of mutual interaction in MRI phased array coils

We describe the use of a computational method for determining the overlap distance minimizing the mutual interaction between two adjacent coils that constitute a part of a phased array system used in MRI. The method is based upon the method of moments, and the analysis is carried out at a target imaging frequency to obtain the overlap distance. For a variety of complex RF phased array coils, we can determine, using the proposed approach, the overlap distance between nearest neighbor block element RF coils such that the mutual interaction is nullified or minimized. We give experimental results to validate the proposed approach. When compared with the experimental data, our theoretical prediction is in excellent agreement.     

Multiple channel phased arrays for echo planar imaging

A new interface combining phased arrays and echo-planar imaging (EPI) technologies was developed for two channel breast MR EPI applications. A detailed design for a dual-channel. EPI-compatible, phased array breast coil is described. EPI digital data multiplexing, signal controlling and sampling schemes are also presented. Results from breast phantoms and patients demonstrate a 55% improvement in signal-to-noise ratio when compared to a conventional two-loop, single channel coil conliguration. This method can be easily expanded to a four or more channel. EPI-compatible, phased array system to improve field-of-view coverage and signal-to-noise ratio.     

A volume adjustable four-coil phased array for high resolution MR imaging of the hip

A four-coil phased array was specifically designed and built for MR imaging of the hip at 1.5 T. Its RF and imaging properties were evaluated using phantom and in-vivo studies and the results were compared to those of three different commercial coils commonly used for hip imaging. Our coil gave a significantly higher S/N at anatomic locations commonly evaluated for hip diagnosis. The increased S/N supports higher image spatial resolution and improves the visualization of fractures and lateral injuries.     

SMASH imaging with an eight element multiplexed RF coil array

SMASH (SiMultaneous Acquisition of Spatial Harmonics) is a technique which can be used to acquire multiple lines ofk-space in parallel, by using spatial information from a radiofrequency coil array to perform some of the encoding normally produced by gradients. Using SMASH, imaging speed can be increased up to a maximum acceleration factor equal to the number of coil array elements. This work is a feasibility study which examines the use of SMASH with specialized coil array and data reception hardware to achieve previously unattainable accelerations. An eight element linear SMASH array was designed to operate in conjunction with a time domain multiplexing system to examine the effectiveness of SMASH imaging with as much as eightfold acceleration factors. Time domain multiplexing allowed the multiple independent array elements to be sampled through a standard single-channel receiver. SMASH-reconstructed images using this system were compared with reference images, and signal to noise ratio and reconstruction artifact power were measured as a function of acceleration factor. Results of the imaging experiments showed an almost constant SNR for SMASH acceleration factors of up to eight. Artifact power remained low within this range of acceleration factors. This study demonstrates that efficient SMASH imaging at high acceleration factors is feasible using appropriate hardware, and that time domain multiplexing is a convenient strategy to provide the multiple channels required for rapid imaging with large arrays.     

基于超声相控线阵的缺陷全聚焦三维成像

在无损检测领域,缺陷三维成像能够还原材料内部缺陷的空间信息,与传统的二维成像相比有着明显的优势。目前实现超声相控阵缺陷三维成像主要依靠面阵探头,而这些设备往往十分复杂和昂贵。通过采取适当的数据采集方法和后处理成像算法,超声相控线阵系统能够实现低成本、高效率的三维超声检测成像。采用断层扫描和全矩阵捕捉的方法获取成像数据;再利用全聚焦成像算法绘制高分辨率的断层图像;根据这些图像在三维空间中真实的位置关系,插值还原出缺陷的三维图像。此外,针对全聚焦成像算法计算量大的问题,提出了一种加速算法。实验表明,这种检测方法能够快速得到目标空间区域的高质量三维图像,准确体现缺陷的空间分布情况,相比于借助B扫查图像和C扫查图像材料内部缺陷的方法,具有更强的直观性。     

Automatic coil selection for channel reduction in SENSE-based parallel imaging

OBJECTIVE: Coil arrays with large number of receive elements allow improved imaging performance and higher signal-to-noise-ratio. The MR systems supporting these arrays have to handle an increased amount of data and higher reconstruction burden. To overcome these problems, data reduction techniques need to be applied, realized either by linear combination of the original coil data prior to reconstruction or by discarding particular data from unimportant coil elements. MATERIALS AND METHODS: This work focuses on the latter approach and presents an efficient algorithm for automatic coil selection applicable to SENSE imaging. A singular value decomposition (SVD)-based coil selection is proposed that performs a coil element ranking quantifying the contribution of each coil element to the image reconstruction allowing appropriate coil selection. This approach makes use of the coil sensitivity information and takes reduction factor and phase encoding direction into account. RESULTS: Simulations, phantom and in vivo experiments were performed to validate the SVD-based coil selection algorithm. The proposed approach proved to be computationally efficient without remarkable image quality degradation. CONCLUSION: The SVD-based approach offers the opportunity for fast automatic coil selection. This could simplify clinical workflow and may, furthermore, pave the way for various 2D real-time and interventional applications.     

基于线阵列超声相控阵三维成像的实现研究

为进一步增强常规超声相控阵的检测能力,弥补二维检测图像对缺陷空间信息反映的单一性,获取更利于分析和评价的工业超声检测三维图像。采用携带编码器的一维线阵列换能器,借助Phascan平台及其二次开发模块采集原始扫查数据,合成带有位置信息的B扫图像,通过基于区域增长技术的混合绘制法实现缺陷的三维重建。人工缺陷对比试块的三维成像测量结果误差多小于5%,实验研究表明,该成像方法和系统能在空间上对缺陷形成一个直观体现,同时能够精确的反映缺陷的位置、形态以及尺寸等信息,为后续实验研究的开展奠定基础。     

改进的机载相控阵雷达JDL-STAP算法

机载相控阵雷达在下视工作时受地杂波的影响较大,虽然空时自适应处理(STAP)技术拥有良好的杂波抑制能力,但其性能依赖于大量的训练样本和高运算量,在现实工程中难以应用.为了弥补STAP算法的不足之处,提出了一种改进的局域联合处理(JDL)降维算法.该方法在构造降维矩阵时,调整了局域处理单元的选取策略,并在主通道对应的杂波...     

超声相控阵检测技术的发展及应用

超声相控阵是近年来发展起来的一门新的工业无损检测技术,通过对各阵元的有序激励可得到灵活的偏转及聚焦声束,联合线性扫查、扇形扫查、动态聚焦等独特的工作方式,使其比传统超声检测具有更快的检测速度与更高的灵敏度,成为目前无损检测领域的研究热点之一。介绍了超声相控阵的检测原理及特点,综述了其国内外发展及研究现状,总结了目前超声相控阵研究热点及发展趋势,最后以汽轮机叶轮轮缘裂纹的检测和焊缝的检测为例,介绍了超声相控阵在实际工程中的应用。     

管道超声相控阵全聚焦成像仿真及算法优化

针对厚壁管道内部缺陷识别困难、可视化差等问题,提出基于超声相控阵理论和全聚焦算法对厚壁管道内部缺陷进行图像重构。并针对全聚焦成像效率低的缺点,采用有限元法对外径为550 mm,壁厚为65 mm的厚壁管道超声相控阵全聚焦成像进行仿真,模拟缺陷检测过程和成像结果,并使用稀疏矩阵对算法进行优化。结果表明：在基本满足成像质量要求的情况下,采用激发中心频率为5 MHz,阵元宽度为 0.5 mm,阵元间距为1 mm,阵元数量为32时,稀疏激发矩阵比全矩阵全聚焦成像效率提高了74.81%,有效提高了成像速度,满足全聚焦快速成像的需求。     

开放式永磁磁共振成像系统中的平板式正交发射线圈的设计

为了提高平板式射频发射线圈的性能,设计了一种正交发射线圈.线圈的结构由优化过程确定,优化目标为产生单位磁场强度所需要的功率,约束条件为成像区域内磁场的均匀度和区域外磁场的快速衰减.为了减小线圈的发射电阻,采用实验方法对导体元件的尺寸和调谐点的分布进行了优化.为了解决单元线圈间的电磁耦合问题,采用了一种π型解耦电路.为一台0.3 T磁共振成像系统实际制作了一个发射线圈,并给出解耦电路的调试结果.     

相控阵天线故障诊断方法研究

随着相控阵天线阵列数目的增加和机载雷达尺寸的增大,故障单元快速诊断的需求日益迫切。本文基于相控阵天线故障诊断的原理,研究了一种相控阵天线故障信号的预处理和诊断方法。首先用矩量法构建了仿真环境;其次利用小波模极大值的方法对信号进行了降噪处理,并提取了时域统计特征和小波能量特征;最后运用层次 SVM诊断方法进行分类,获得更高的准确率。实验表明,在信噪比不同的情况下,分类正确率呈现稳步提高的趋势。理论上证明该方法能够有效诊断相控阵阵元故障。     

Basic considerations on the impact of the coil array on the performance of Transmit SENSE

Transmit SENSE adapts the idea of parallel imaging to RF transmission. Using multiple independent transmit coils, the duration of a spatially selective RF pulse can be reduced. It is known from parallel imaging that a suboptimal coil-array geometry might lead to an ill-conditioned sensitivity matrix and, thus, to a non-homogenous noise amplification in the resulting image. The current paper investigates the consequences of suboptimal coil arrays for Transmit SENSE. Two possible consequences of a suboptimal coil array are studied in the framework of numerical simulations: the incorrect excitation of the desired spatial pattern and the increase of the specific energy absorption rate (SAR), i.e. the RF power required to excite the desired pattern. Incorrect pattern excitation occurs only in pathologic coil-array scenarios. The increase of the SAR is very moderate for a large range of coil-array geometries. Using spiral excitation k-space trajectories leads to superior results compared to Cartesian trajectories. The problem of an ill-conditioned matrix inversion does not seem to play a major role in Transmit SENSE. Consequently, the freedom in designing coil arrays seems to be much larger in Transmit SENSE than in SENSE in the receive mode.     

A low-loss compact six-bit DMTL phase shifter for phased array antenna applications

A phase shifter is one of the main components of radars and phased array systems. In this paper, a novel three-state two-bridge unit cell is presented for a compact low-loss six-bit distributed microelectromechanical systems (MEMS) transmission line (DMTL) phase shifter. The proposed unit cell includes a coplanar waveguide (CPW) transmission line, a MEMS bridge on the signal line, two metal-air-metal (MAM) capacitors on a glass substrate, and two additional electrodes under the MEMS bridge, near the signal line. Using these electrodes, it is possible to generate two different phase states employing the MEMS bridge, and the third state is produced by a metal-air-metal (MAM) bridge. Hence, the designed structure can generate three different phase shifts per unit cell (i.e., 5.625°, 11.25°, and 22.5° phase shifts). The novelty of this design is that the number of unit cells is considerably reduced from 64 in a conventional six-bit phase shifter to only 17 in our design. Therefore, the total length of the six-bit phase shifter and average loss are considerably reduced. The designed structure is calculated and simulated at 32 GHz using MATLAB and ANSOFT HFSS, respectively. According to the calculation and simulation results, the lateral size of the phase shifter is only 8.5 mm, the root mean square (RMS) phase error is 1.38°, and the average loss is 1.1 dB. The feasibility of the proposed design is investigated using the proposed fabrication process. The designed phase shifter can be easily scaled to other frequencies for radar and satellite applications with more bits.     

Visualization of cardiac involvement in patients with systemic sarcoidosis applying contrast-enhanced magnetic resonance imaging

5. Summary Contrast-enhanced MRI may serve as a sensitive noninvasive tool for the detection and follow-up of myocardial involvement in patients with systemic sarcoidosis.     

基于压缩感知的稀疏阵列近景微波三维成像

近景微波成像技术在隐藏武器检测、生物医学成像、无损检测等领域具有广阔的应用前景.将压缩感知理论应用于近景微波成像系统,提出了基于稀疏阵列天线的三维成像几何及相应的回波模型,该几何通过高度向的稀疏阵列电子扫描、方位向的机械扫描及距离向发射宽带信号来实现三维分辨;文中将压缩感知理论应用于稀疏阵列三维成像,提出了基于压缩感知...     

基于一发多收线圈阵列的频域电磁法未爆弹探测技术

为了实现未爆弹目标的高效探测及定位,开发了一种小回线激励-阵列式线圈接收的主动电磁探测系统。采用偏心结构的收发线圈配置,实现了一次场的对消。通过接收线圈阵列排布,有效地提高了系统探测效率。提出了一种基于阵列线圈响应差分比较的未爆弹目标水平位置定位方法,并实验验证了可行性。研究结果表明,探测系统对于典型环状金属柱体的探测深度达到1 m,定位方法的计算值与真值误差在3.76 cm,实现了对未爆弹目标的准确探测和定位。     

Research on magnetron phased array with mutual injection locking for space solar power satellite/station

The SPS (Space Solar Power Satellite/Station) will be a clean base‐load power station in space. It will be the largest space system ever built and will require a high‐efficiency, large‐size, highly accurate, lightweight, inexpensive phased array in order to transmit energy generated in space to the ground. We have proposed and developed a phase‐controlled magnetron (PCM) with injection locking and PLL technique for the high‐efficiency, lightweight, inexpensive phased array. It still has several weak points: (1) approximately 10% power loss occurs at the circulator for injection locking, (2) phase shifter is needed in each PCM for the phased array. In order to correct the weak points, we propose a magnetron phased array with mutual injection locking. For the magnetron phased array, we only use two PCMs with phase shifters; the other components are self‐oscillated and mutual injection locked magnetrons. In this paper, we propose a new formula for use with the magnetron phased array with mutual injection locking. We also present the results of experiments on beam direction control with the magnetron phased array with mutual injection locking. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(2): 21–32, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20998     

基于CPCI总线的相控阵雷达波束调度系统设计

为了解决传统相控阵雷达波束调度系统工作不够灵活、不够高效,以及信息传输效率不高、易受干扰等缺点,提出了一种新型的基于CPCI总线的波束调度系统体系结构,采用了在实时系统VxWorks下的CPCI设备驱动、DMA数据传输等技术,充分利用了软件编程的灵活高效,提高了系统的传输效率和质量。工程实践表明,此体系结构可以高效、稳定的保证波束调度软件系统乃至相控阵雷达整机系统正常工作。