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.     

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.     

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。     

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.     

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...     

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.     

Basic pulse sequences for fast cardiac MR imaging

3. Summary Technical challenges of cardiac MRI include minimizing the effects of cardiac and respiratory motion and developing techniques that allow for both high spatial resolution and high SNR given the small size of small structures such as the coronary vessels. Fast imaging techniques provide considerable time savings and increased flexibility which allow to further optimize image quality.     

Prediction of pathological tumor volume in clinically localized prostate cancer: value of endorectal coil magnetic resonance imaging

The purpose of this study was to determine whether endorectal coil magnetic resonance imaging (MRI) enables accurate assessment of pathologic tumor volume in patients with clinically localized prostate carcinoma. Twenty-four patients with biopsy-proved prostate carcinoma underwent MRI at 0.5 T before radical prostatectomy. Tumor volumes were determined independently on axial fast-spin-echo (SE) T₂-weighted MR images and whole-mount pathology slides of the surgical specimens. At pathology, tumor volumes ranged from 0.17 to 9.42 cm³ (mean±SD, 3.11±2.99 cm³). A strong correlation (r=.944) was found between measurements of tumor volume based on MR images and pathological specimens. The error was less than 0.5 cm³ in 14 cases, in the range of 0.5–1 cm³ in 7 cases, and more than 1 cm³ in 3 cases. By using an MR tumor volume of 2 cm³ as cutoff value, extracapsular tumor spread could be predicted with a sensitivity of 81.2%, a specificity of 100%, and an accuracy of 87.5%. Tumor volume determinations based on MR images seem to be accurate enough to be helpful in clinical decision-making.     

Measurements of left ventricular dimensions using real-time acquisition in cardiac magnetic resonance imaging: comparison with conventional gradient echo imaging

This study investigates the use of real-time acquisition in cardiac magnetic resonance imaging (MRI) for measurements of left ventricular dimensions in comparison with conventional gradient echo acquisition. Thirty-one subjects with a variety of left ventricular morphologies to represent a typical clinical population were studied. Short-axis data sets of the left ventricle (LV) were acquired using a conventional turbo-gradient echo and an ultrafast hybrid gradient echo/echo planar sequence with acquisition in real-time. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF) and left ventricular mass (LV mass) were measured. The agreement between the two acquisitions and interobserver, intraobserver and interstudy variabilities were determined. The bias between the two methods was 5.86 ml for EDV, 0.23 ml for ESV and 0.94% for EF. LV mass measurements were significantly lower with the real-time method (mean bias 14.38 g). This is likely to be the result of lower spatial resolution and chemical shift artefacts with the real-time method. Interobserver, intraobserver and interstudy variabilities were low for all parameters. In conclusion, real time acquisition in MRI can provide accurate and reproducible measurements of LV dimensions in subjects with normal as well as abnormal LV morphologies, but LV mass measurements were lower than with conventional gradient echo imaging. Presented in abstract form at the International Society of Magnetic Resonance in Medicine meeting in Denver, Colorado in April 2000.     

孔径合成式辐射成像系统中阵列因子的作用

文中讨论了孔径合成式辐射成像系统中阵列因子的定义,并利用阵列因子分析了理想情况下成像系统中涉及到的一些性能指标,同时给出了相应的仿真结果。     

Recent advances in image reconstruction, coil sensitivity calibration, and coil array design for SMASH and generalized parallel MRI

Parallel magnetic resonance imaging (MRI) techniques use spatial information from arrays of radiofrequency (RF) detector coils to accelerate imaging. A number of parallel MRI techniques have been described in recent years, and numerous clinical applications are currently being explored. The advent of practical parallel imaging presents various challenges for image reconstruction and RF system design. Recent advances in tailored SiMultaneous Acquisition of Spatial Harmonics (SMASH) image reconstructions are summarized. These advances enable robust SMASH imaging in arbitrary image planes with a wide range of coil array geometries. A generalized formalism is described which may be used to understand the relations between SMASH and SENSE, to derive typical implementations of each as special cases, and to form hybrid techniques combining some of the advantages of both. Accurate knowledge of coil sensitivities is crucial for parallel MRI, and errors in calibration represent one of the most common and the most pernicious sources of error in parallel image reconstructions. As one example, motion of the patient and or the coil array between the sensitivity reference scan and the accelerated acquisition can lead to calibration errors and reconstruction artifacts. Self-calibrating parallel MRI approaches that address this problem by eliminating the need for external sensitivity references are reviewed. The ultimate achievable signal-to-noise ratio (SNR) for parallel MRI studies is closely tied to the geometry and sensitivity patterns of the coil arrays used for spatial encoding. Several parallel imaging array designs that depart from the traditional model of overlapped adjacent loop elements are described. Summary of material presented at the 2001 ISMRM workshop on MRI hardware, Cleveland, OH, USA.     

Breathhold imaging of the upper abdomen using a circular polarized-array coil: comparison with standard body coil imaging

Current studies emphasize the use of array coils to decrease noise and increase the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). We applied Tl-weighted and T2-weighted standard nonbreathhold spin echo (SE) sequences and Tl-weighted FLASH, TurboFLASH, T2-weighted spin-echo time (TSE), and heavily T2-weighted half Fourier acquisition single-shot TSE (HASTE) sequences during breathhold for abdominal imaging in 15 normal volunteers. The breathhold scans were performed using both a standard coil and a circular polarized array coil. We analyzed the signal intensity (SI), SNR, and CNR of abdominal organs in all sequences. SNRs increased in all cases by an overall factor of 3 due to an 8% increase in overall Sis and a 50% decrease in noise when applying the array coil. Although the array-coil FLASH sequence performed at least as well as the respective SE sequence, the SNRs of the array-coil TurboFLASH, TSE breathhold, and HASTE sequences were generally lower. We conclude that array-coil imaging significantly improves fast imaging of the abdomen.     

Magnetic resonance imaging of the female pelvic floor and urethra: body coil versus endovaginal coil

The anatomy of the female pelvic floor and urethra is complex. With the introduction of MRI, the discussion about the normal anatomy of this area has not diminished. The use of a body coil may be contributary to this. In the present study images obtained with an endovaginal coil are compared with those of a quadrature body coil series to study the possible advantages of endovaginal imaging. Axial and radial T₂-w TSE images at a 1.0-T machine were obtained in seven healthy volunteers. The pelvic floor structures as well as the levator ani muscle and the urogenital diaphragm are excellently demonstrated with the endovaginal coil. Also, the urethrovaginal sphincter could be recognized in six volunteers, but only in three with the body coil. In six volunteers a new ligamentous structure, the urethropelvic sling, connecting the urethra to the levator ani muscle and contributing to the supporting mechanism of the urethra is shown with the endovaginal coil. The zonal anatomy of the urethra is excellently shown with the endovaginal coil. The urethral length could only be accurately measured with this coil and ranged from 3.1 to 3.6 cm. Compared with the body coil, endovaginal MRI is excellent in demonstrating the anatomy of the pelvic floor and urethra.     

A novel MEMS-based focal plane array for infrared imaging

On the basis of opto-mechanical effect and micro electromechanical system (MEMS) technology, a novel substrate-free focal plane array (FPA) with the thermal isolated structure for uncooled infrared imaging is developed, even as alternate evaporated Au on SiN cantilever is used for thermal isolation. A human thermal image is obtained successfully by using the infrared imaging system composed of the FPA and optical detecting system. The experiment results show that the realization of thermal isolation structure in substrate-free FPA increases the temperature rise of the deflecting leg effectively, whereas the noise equivalent temperature difference (NETD) is about 200 mK. Translated from Chinese Journal of Semiconductors, 2006, 27(1): 150–155 [译自: 半导体学报]