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磁共振成像系统中射频线圈的优化设计 总被引:2,自引:2,他引:2
射频线圈是磁共振成像系统中拾取信号的核心元件。在线圈设计过程中,可以以优化信噪比为目标求解源电流的分布。文中利用磁偶极子的概念,将分布在有限的平面或圆柱面上的电流进行分解,构造基线圈,并引入一个环路基线圈处理圆柱面上的环形电流情况;然后通过源电流分布和基线圈电流分布之间的映射关系,求解使得来自空间某点信号的信噪比最优时的源电流分布。应用这一原理计算了一个源电流分布在圆柱表面上的实例以及工程实际中射频线圈信噪比的物理上限,并讨论如何利用这一结果对线圈的信噪比性能进行评估。 相似文献
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梯度线圈是磁共振系统的核心部件之一,其产生的梯度磁场是成像空间定位的物理基础。在开放式磁共振系统中,大量铁磁介质会导致实际梯度磁场偏离设计值,因此需要对实际梯度磁场进行校验。本文针对开放式磁共振的结构特点,提出了一种基于扇环形状单元的积分方程法,可以计算二维/三维模型中的梯度磁场。针对两种常见的开放式磁共振结构,通过将本文方法的计算结果与其他三种方法(直接法、镜像法和有限元法)进行对比,证明了本文方法在保证计算精度的同时,可以大幅减少计算时间,在重复计算和迭代优化中具有显著优势。实验结果证明了该算法具有良好的可靠性。 相似文献
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MRI射频线圈的发射效率 总被引:3,自引:0,他引:3
随着磁共振成像技术的发展 ,发射线圈的效率也要求提高 ,正交线圈能产生高效率的圆极化磁场 ,圆极化发射与传统的线极化发射相比 ,功率消耗减小一半 ,而且发射磁场的均匀度很高 ,椭圆极化的发射效率介于线极化和圆极化之间 ,采用圆极化发射方式 ,能提高射频线圈的发射效率 相似文献
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射频(RF)线圈是磁共振成像(MRI)系统的关键部件之一,用于射频信号的发射或接收,乳腺3 T MRI中采用专用的射频线圈可进一步提高磁共振成像的质量。为了获得简单的线圈绕线形状并使得射频磁场分布均匀,研究利用了L曲线自动选取和手动选取惩罚因子对线圈绕线形状和磁场分布均匀性的影响,并结合目标场方法和流函数方法,提出了一种用于3 T(磁感应强度为3 T)乳腺磁共振成像的射频线圈设计方法。研究结果表明:1×1、2×1、2×2、4×1等4种半球形相控阵射频线圈的绕线形状随着阵列增加而变复杂;惩罚因子取利用L曲线自动选取的值时,磁感应强度线性方程的解最精确,阵列1×1在[10-25,10-18]区间内无论怎样选取惩罚因子,灵敏区内的磁场分布误差(即实际值与理想值之间的误差)都40%,阵列2×2和4×1的磁场分布误差10%,但是线圈绕线形状非常复杂,工程上难以实现;手动选取惩罚因子的值,可以使得磁场分布误差40%,而且线圈的绕线形状简单;与相同半径和高度的圆柱型射频线圈相比,所提出的半球型射频线圈磁场分布更为均匀。可得结论:惩罚因子越小,则线圈绕线越复杂,而磁场分布越均匀;反之,惩罚因子越大,则线圈绕线越简单,而磁场分布越不理想。在简单的线圈绕线形状和保证射频磁场分布均匀之间取得平衡需要根据L曲线手动调节选取惩罚因子的值。 相似文献
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磁共振模式无线电能传输系统建模与分析 总被引:5,自引:0,他引:5
针对磁共振模式无线电能传输系统功率和效率计算问题,利用互感耦合模型,对磁共振模式电能传输系统的4种拓扑进行分析,得出了系统的传输功率及其计算模型,并进一步分析了系统传输效率与线圈谐振频率、互感系数、线圈内阻等参数之间的关系,为磁共振模式无线电能传输系统的设计及参数优化提供了理论依据。为验证理论分析的正确性,制作了一个磁共振模式无线电能传输装置,该装置实现了80 cm内60 W的无线能量传输,且传输效率达到了52%。 相似文献
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采用目标场方法设计了一组超导核磁共振成像系统梯度线圈.该梯度线圈固定在半径为0.8 m、长3m的圆柱形骨架上,目标区域位于该圆柱中心,半径为0.2 m,梯度场强为40 mT/m.在该方法中,电流密度在柱坐标系下被分解为三角级数之和,接着通过Biot-Savart定律求出轴向磁场强度表达式,再通过基于目标场的Tikhonov正则化算法把待定三角系数的求解问题转化成线性方程组的求解,并通过流函数技术得到线圈的实际绕线分布,最后进行磁场偏差分析,分析结果表明,所设计线圈的磁场偏差远远小于通常所要求的5%.此外,该方法不仅适用于柱面梯度线圈设计,对于超导磁共振成像系统的有源匀场线圈设计也同样适用. 相似文献
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目前临床上烧伤深度判断缺少合适的检测设备和方法,主要由烧伤科医生主观判断,准确率不高。该文设计了一种用于烧伤深度判断的单边核磁共振浅层成像磁体系统,对该磁体系统的单边磁体结构、平面梯度线圈、射频线圈以及射频屏蔽进行了优化设计。采用该磁体系统对橡皮模型和猪皮烧伤模型进行成像实验,获得了两种模型的二维成像。结果表明由该磁体系统获得的图像与橡皮实验模型的形状相似,且图像中不同烧伤深度部分和正常对照部分的信号强度呈鲜明对比,初步证明该文设计的单边磁共振浅层成像磁体系统可用于皮肤烧伤深度的检测。 相似文献
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电流域标量处理法在横向磁场电机三维磁场分析中的应用 总被引:1,自引:0,他引:1
横向磁场电机具有电磁解耦、设计灵活、输出力密度大等优点,引起广泛关注.但是该种电机磁路复杂,需采用三维场分析.在三维有限元磁场中如果对电流区域进行适当处理,采用标量磁位进行分析,可以比采用矢量磁位大大提高计算速度.本文首先对任意形状的电流区域在不同坐标系下的一般处理方法进行了系统推导;然后,将该一般方法进一步应用于特殊情况下的电流区域,使得问题得到简化;最后,根据所推导的原理编制三维有限元软件,利用该软件对样机磁场进行计算,试验结果表明了该方法的正确性. 相似文献
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ABSTRACT This paper presents a general finite element method for the solution of fields due to general three-dimensional vector-valued sources in terms of the magnetic scalar potential, between boundaries of axisymmetric shape. In the space occupied by the sources, and there only, a correction field defined by a vector quantity must be added. This correction field is obtained by using a vector potential ā, subject to the Coulomb convention. The latter convention may be relaxed to allow ā to be divergenceless in the mean. In many magnetic field problems, the sources (current-carrying coils), occupy only a small part of the problem region. Since the correction field is non-zero only in the current-carrying space, it is computationally relatively cheap to find. Use of the procedure is illustrated by the end winding model of an electric machine. 相似文献
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本文探索了一种适用于工程计算的温升计算方法,它避免了用有限元法计算时因种种假定所带来的误差。提供了分析1000MW级水氢氢汽轮发电机转子端部线圈各段的压力损失和节点单元温升的分析计算方法。考虑到电机绕组的对称性;将二分之一极绕组分成mxn个温度计算单元,建立了准三维热模型,给出了绕组节点单元热等效网络和任一节点单元导体的热2方程,用数值法计算了一 台930MW4极水5氢氢汽轮发电机,将计算值与试验 相似文献
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Background Quadrature surface MRI/MRS detectors comprised of circular loop and figure-8 or butterfly-shaped coils offer improved signal-to-noise-ratios
(SNR) compared to single surface coils, and reduced power and specific absorption rates (SAR) when used for MRI excitation.
While the radius of the optimum loop coil for performing MRI at depth d in a sample is known, the optimum geometry for figure-8 and butterfly coils is not.
Materials and methods The geometries of figure-8 and square butterfly detector coils that deliver the optimum SNR are determined numerically by
the electromagnetic method of moments. Figure-8 and loop detectors are then combined to create SNR-optimized quadrature detectors
whose theoretical and experimental SNR performance are compared with a novel quadrature detector comprised of a strip and
a loop, and with two overlapped loops optimized for the same depth at 3 T. The quadrature detection efficiency and local SAR
during transmission for the three quadrature configurations are analyzed and compared.
Results The SNR-optimized figure-8 detector has loop radius r
8 ~ 0.6d, so r
8/r
0 ~ 1.3 in an optimized quadrature detector at 3 T. The optimized butterfly coil has side length ~ d and crossover angle of ≥ 150° at the center.
Conclusions These new design rules for figure-8 and butterfly coils optimize their performance as linear and quadrature detectors.
This work is supported by NIH grant R01 RR15396. 相似文献
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Object Internal MRI coils have important applications in diagnostic and interventional studies. Since they can be placed very close
to the region of interest in the body, they are favored over external coils in applications where high-resolution images are
required. In this paper it is demonstrated that ultimate intrinsic SNR (UISNR) and the optimum coil sensitivity solutions
can be used to make new coil designs with higher intrinsic SNR.
Materials and methods In this study, UISNR, which is the maximum attainable value of the intrinsic SNR, is used as a measure of performance and
as a design criterion. As an example, a novel endorectal MRI coil is designed. The design is tested with phantom and patient
studies.
Results An endorectal coil is built to demonstrate the effectiveness of the design strategy. ISNR of the endorectal coil approximates
the UISNR to 72%.
Conclusion An internal coil design method that takes advantage of the UISNR and optimum coil sensitivity calculations was presented.
This method can also be used to design better internal MRI coils for different applications. 相似文献
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We describe the use of liquid helium-cooled (4.2 K) gradiometer coils and a DC superconducting quantum interference device
(SQUID) preamplifier to improve the SNR of magnetic resonance imaging (MRI) at 0.01 T. Gradiometer windings are used both
to reduce lossy interactions with the MRI system's room temperature magnet and gradient coils and also to reject interference
from more distant sources, which reduces the need for RF shielding. We have tested both axial and planar (figure-of-eight)
gradiometer configurations. The figure-of-eight gradiometer has a more rapid fall-off in sensitivity with increasing distance
from its windings than the axial gradiometer, but this is compensated for by reduced lossy interactions and improved interference
rejection. We have used the system to image the human arm. 相似文献
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Trumper D.L. Won-Jong Kim Williams M.E. 《Industry Applications, IEEE Transactions on》1996,32(2):371-379
This paper presents a design and analysis framework for the general class of permanent magnet electric machines. In the authors' analysis, surface-mounted linear motors consisting of permanent magnets and ironless current-carrying coils are treated in a uniform way via the magnetic vector potential. This analysis is developed to design novel linear magnetic levitators for driving precision motion control stages such as those used in wafer steppers. For one such motor structure, they give analytical formulae for its magnetic field, force, flux linkage, inductance of the winding, and back electromotive force. They provide experimental results with a six degree-of-freedom magnetic levitator. These results are in good agreement with analytical estimations. The levitator uses a permanent-magnet Halbach array in order to improve its power efficiency. By analogy, there also exists an electromagnetic dual of the Halbach array. One such dual utilizes a triangular winding pattern in order to achieve a primarily single-sided magnetic field 相似文献