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1.
李磊  徐俊成  蔡昕  蒋瑜 《磁共振成像》2016,7(6):449-453
目的介绍一种用于消除磁共振线圈通道间耦合的仿真方法,指导猕猴脑部线圈的设计。材料与方法通过电磁场及电路仿真软件,计算线圈周围的空间电磁场分布及S参数,以观测通道间的耦合影响。结果在猕猴脑部接收线圈的设计过程中,通过仿真通道间的耦合可知:当相邻一组线圈的几何中心相距42.2 mm时,其耦合影响可以忽略不计,达到了线圈的设计要求。结论利用本文介绍的仿真方法,实现了猕猴脑部多通道线圈的去耦设计。在线圈的制作过程中,该方法可以明确优化方向,降低线圈的研发成本。  相似文献   

2.
背景:目前的核磁共振图像不可避免会有灰度偏差场存在,会对医学图像的计算机数字处理产生非常不利的影响,如分割、配准、量化等.因此对于这种不利的空间密度变化的修正成为许多图像分析任务必要的预处理步骤.目的:提出一种以图像数据为基础不依赖于模板的复杂图像信号偏差场的修正方法.方法:数据是来源于首都医科大学复兴医院放射影像科,采集于美国GE公司核磁共振设备,所有图像来源于志愿者的核磁共振图像.成像视野250 mm×250 mm,矩阵256×256,层厚1 mm.对核磁共振图像处理目标进行锁定的Mask方法,并借助信息熵的方法实现对核磁共振图像灰度偏差场的有效修正. 结果与结论:通过核磁共振图像实验,证明该方法可以有效准确地修正核磁共振图像灰度偏差场的伪影.实验结果为核磁共振图像计算机分析提供了一种有效的修正灰度偏差场方法,提高了图像分析的准确性和鲁棒性.  相似文献   

3.
目的 提出一种适用于小动物整个头部成像的高场射频线圈设计方法,以解决表面线圈在脑深部区域信噪比低的问题.方法 采用微波传输带结构,并集成了猫头部固定系统.根据设计结果制作的原型线圈由16个微波传输带单元构成.分别采集了矿物油、水模以及猫脑图像验证线圈性能.结果 猫脑感兴趣区域内信噪比及敏感度分布均匀;功能磁共振成像结果清楚显示了连接外侧膝状核及初级视皮层的丘脑皮层视觉网络.结论 MTL线圈的动物固定系统能够稳定地固定猫头部,减小运动伪影,提高图像质量;该线圈适用于脑功能磁共振研究,尤其是脑深部区域的fMRI研究.  相似文献   

4.
磁共振成像射频线圈的设计及仿真   总被引:3,自引:1,他引:2  
目的 探讨0.3T永磁MRI系统中笼式线圈的计算机模拟和优化.方法 运用毕奥-萨伐尔定律,通过计算分析,设计了针对3H,129Xe共振频率的8列高通笼式线圈,利用IDL软件进行相关计算和仿真.结果 仿真结果证明了在低场条件下所设计的8列笼式高通线圈产生的射频磁场的均匀性和对称性.当列线数目减少为6列及4列时,笼式线圈产生的磁场均匀性和对称性大大降低.结论 仿真精确度较好,误差较低.线圈列数的降低对B1场均匀性造成破坏.  相似文献   

5.
目的 利用1.5T MR扫描仪寻求简单易行的体外冠状动脉管壁成像程序.方法 对10个猪心行冠状动脉MR检查.以3D FIESTA序列行前降支成像,分别选择8通道头部线圈、膝关节线圈、颞下颌关节表面线圈行2D SE T1WI, 成像参数均相同,之后用颞下颌关节表面线圈,采用384×256和512×512的矩阵行T1WI.注入对比剂后,分别使用不同的NEX行SE T1WI、PDWI和frFSE T2WI.测量前降支近段管壁、管腔、前降支周围心外膜下的脂肪结缔组织、前降支邻近的室间隔心肌的信号强度,并测量周围空气的信号强度作为背景噪声,计算图像的信噪比(SNR)和冠状动脉管壁对管腔的对比噪声比(CNR1)及冠状动脉管壁对周围心外膜下脂肪结缔组织的对比噪声比(CNR2).结果 颞下颌关节表面线圈成像前降支管壁SE T1WI的SNR和CNR1、CNR2明显高于8通道头线圈和膝关节线圈.384×256矩阵所得的SE T1WI的SNR和CNR1、CNR2明显高于512×512矩阵.NEX为3时图像的SNR和CNR1、CNR2最高.结论 选择颞下颌关节表面线圈、384×256的矩阵、3个NEX可以得到良好的SNR和CNR.  相似文献   

6.
扩散加权像变形矫正技术的相关多因素分析   总被引:1,自引:0,他引:1  
目的探讨扩散加权像变形的矫正模具位置、扩散敏感梯度大小、方向、匀场方式对扩散参数图原始图像变形的影响,为开发矫正装置与方法提供依据.方法采用自制25点空间定位模具,分别放置在环形极化线圈的中心与偏中心位置,针对每个位置(β因素),在测量前进行主动匀场,在三个垂直方向(α因素)施加b(扩散敏感系数) 为0~1000 s/mm2的Gb,b大小以100 s/mm2步进增加(γ因素).利用坐标变换得到各图的变形矫正公式,通过多因素方差分析明确各个因素与矫正公式各个系数间的关系.结果在X,Y方向的变形矫正公式如下:X=X1 X2X' X3Y'; Y=Y1 Y2X' Y3Y'.除X3外,各个系数均与方向(α)、位置(β)有关.刚体位移与b值有关.弹性位移与b值(γ)无关(P无显著性差异).位置(β)与b值(γ)的交互作用影响刚体位移.在扩散敏感系数在700的情况下,Gb s不引起明显的层面内位移, 而Gb r,p主要导致在Y方向的位移.模具中心匀场情况下变形最小.结论在扩散敏感系数在模具中心匀场700的情况下,Gb r,p的作用主要表现为沿相位编码方向的刚性平移.当取0~1000 s/mm2范围内的其他Gb值时,可以得到同一类型校正公式,只是刚体位移值会不同.匀场情况下,对各个DWI图像的层层对应配准是有效的变形矫正方法.  相似文献   

7.
目的 研究3.0T磁共振成像系统中大鼠脑部射频线圈.方法 提出一种设计线圈结构的方案,采用高等于直径的鞍型线圈,研究直径为5 cm的大鼠脑部线圈减小电容和分布电容,可使线圈带宽减小,提高线圈品质的因素(Q).将线圈与人体头部线圈和体部线圈分别对自制的模型利用同一序列进行扫描,对三组图像选择同一位置的图像,比较各线圈的信噪比(SNR).观察图像的质量,应用大鼠颅脑模型分别进行轴位、矢状位和冠状位T1W FLAIR或T2W扫描.结果 线圈的SNR比现有的头部线圈高5倍以上.大鼠图像能很好地显示脑室结构,可清楚分辨脑部的灰质和白质.结论 利用所设计的线圈可获得具有很高SNR的图像,在大鼠脑部影像研究中取得了很好的效果.  相似文献   

8.
利用逆向迭代法修正MRI图像中刚性运动伪影的研究   总被引:2,自引:1,他引:1  
目的提出逆向迭代修正法(IIC)和基于直方图的熵准则函数,消除MRI图像中刚性平移运动伪影.方法利用该熵函数建立的准则,IIC方法通过两个连续的步骤来消除仿真运动伪影:①在所有可能的运动方向上添加逆向相位差;②利用熵判断函数估计出实际的运动方向和位移,从而消除运动伪影.结果为了检验方法的可行性,通过对模板和医学图像的仿真实验,验证了逆向迭代修正法(IIC)和基于直方图的熵准则函数的有效性和精确性.结论 IIC方法能够有效消除MR图像刚性平移运动伪影.  相似文献   

9.
目的 评价双源射频发射技术在提高3.0TMR心脏局部射频场均匀性和心脏成像质量中的优势.方法 对14名健康成年志愿者行双源和单源射频发射左心室短轴位射频场匀场和电影成像(B-TFE序列),其中双源电影成像采用不同TR/TE和FA分别得到3组图像.利用配对t检验评价射频场的均匀性,以单因素方差分析比较心室腔-室间隔信号对比度(CR)之间的差异.由2名医师对图像伪影进行评分,采用Wilcoxon秩和检验比较评分差异,对评价者间的一致性采用Kappa检验.结果 双源射频发射技术显著改善了B1场的均匀性,提高了B-TFE序列心室腔-室间隔的CR(P<0.05),应用短TR双源射频发射技术图像伪影明显减少(P<0.05),评价者间的一致性均高度一致.结论 双源射频发射技术在3.0TMR心脏成像中有一定优势,可以提高射频场均匀性,增加血池-心肌CR,减少伪影.  相似文献   

10.
文章提出了一种基于手术空间和图像空间自动配准的手术计划系统设计和实现方法:①选取3个有一定间隔的横断面.②使用模板匹配法自动识别每一个横断面上的标志点.③用识别的数据建立手术空间和图像空间的刚体变换模型,再用最小二乘法解方程组得到两个空间的最优变换矩阵和平移矩阵.最后再通过建立脑空间和图像空间映射关系来计算功能靶点坐标.基于以上算法设计了手术计划系统软件,对比了手动和自动方法识别标志点的运行时间,并设计系统改进前后功能靶点计算值和手术空间实际测量值对比实验.结果证明以上方法有较好的靶点计算速度和精度.  相似文献   

11.
Radiative antenna techniques, e.g., dipole and monopole, have been proposed for radiofrequency (RF) coil array designs in ultrahigh field MRI to obtain stronger B1 field and higher signal‐to‐noise ratio (SNR) gain in the areas deep inside human head or body. It is known that element decoupling performance is crucial to SNR and parallel imaging ability of array coil and has been a challenging issue in radiative antenna array designs for MR imaging. Magnetic wall or induced current elimination (ICE) technique has proven to be a simple and effective way of achieving sufficient decoupling for radiative array coils experimentally. In this study, this decoupling technique for radiative coil array was analyzed theoretically and verified by a simulation study. The decoupling conditions were derived and obtained from the theory. By applying the predicated decoupling conditions, the isolation of two radiative elements could be improved from about ? 8 dB to better than ? 35 dB. The decoupling performance has also been validated by current distribution along the radiative elements and magnetic field profiles in a water phantom. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 183–190, 2015  相似文献   

12.
Fetal MRI on 1.5T clinical scanner has been increasingly becoming a powerful imaging tool for studying fetal brain abnormalities in vivo. Due to limited availability of dedicated fetal phased arrays, commercial torso or cardiac phased arrays are routinely used for fetal scans, which are unable to provide optimized SNR and parallel imaging performance with a small number coil elements, and insufficient coverage and filling factor. This poses a demand for the investigation and development of dedicated and efficient radiofrequency (RF) hardware to improve fetal imaging. In this work, an investigational approach to simulate the performance of multichannel flexible phased arrays is proposed to find a better solution to fetal MR imaging. A 32 channel fetal array is presented to increase coil sensitivity, coverage and parallel imaging performance. The electromagnetic field distribution of each element of the fetal array is numerically simulated by using finite-difference time-domain (FDTD) method. The array performance, including B(1) coverage, parallel reconstructed images and artifact power, is then theoretically calculated and compared with the torso array. Study results show that the proposed array is capable of increasing B(1) field strength as well as sensitivity homogeneity in the entire area of uterus. This would ensure high quality imaging regardless of the location of the fetus in the uterus. In addition, the paralleling imaging performance of the proposed fetal array is validated by using artifact power comparison with torso array. These results demonstrate the feasibility of the 32 channel flexible array for fetal MR imaging at 1.5T.  相似文献   

13.
Design of magnetic resonance imaging (MRI) radiofrequency (RF) coils using lumped circuit modeling based techniques begins to fail at high frequencies, and therefore more accurate models based on the electromagnetic field calculations must be used. Field calculations are also necessary to understand the interactions between the RF field and the subject inside the coil. Furthermore, observing the resonance behavior of the coil and the fields at the resonance frequencies have importance for design and analysis. In this study, finite element method (FEM) based methods have been proposed for accurate time‐harmonic electromagnetic simulations, estimation of the tuning capacitors on the rungs or end rings, and the resonant mode analysis of the birdcage coils. Capacitance estimation was achieved by maximizing the magnitude of the port impedance at the desired frequency while simultaneously minimizing the variance of RF magnetic field in the region of interest. In order for the proposed methods to be conveniently applicable, two software tools, resonant mode and frequency domain analyzer (RM‐FDA) and Optimum Capacitance Finder (OptiCF), were developed. Simulation results for the validation and verification of the software tools are provided for different cases including human head simulations. Additionally, two handmade birdcage coils (low‐pass and high‐pass) were built and resonance mode measurements were made. Results of the software tools are compared with the measurement results as well as with the results of the lumped circuit modeling based method. It has been shown that the proposed software tools can be used for accurate simulation and design of birdcage coils. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 13–32, 2015  相似文献   

14.
目的 选择合适的脉冲线圈以获得清晰的腹部磁共振图像。方法 14例病人采用体线圈和体部相控阵线圈分别进行腹部磁共振扫描,两种线圈 的扫描序列完全一致,比较两种线圈所获图像的质量。结果 用相控阵线圈采集的腹部磁共振图像的平均信噪比明显高于体线圈所获图像(P<0.05)。结论 利用体部相控阵线圈可明显提高腹部磁共振图像的质量。  相似文献   

15.
Both higher magnetic field strengths (> or =3 T) and multiple receiver "array coils" can provide increased signal-to-noise ratio (SNR) for MRI. This increase in SNR can be used to obtain images with higher resolution, enabling better visualisation of structures within the human brain. However, high field strength systems also suffer from increased B(1) non-uniformity and increased power deposition, reaching specific absorption rate (SAR) limits more quickly. For these problems to be mitigated, a careful choice of both the pulse sequence design and transmit RF coil is required. This paper describes the use of a prototype array coil consisting of 4 irregularly shaped coils within a standard configuration for neuroimaging at 4.7 T (a head transmit/receive volume coil to minimise SAR and a head gradient insert for maximum gradient performance). With a fast spin echo (FSE) pulse sequence optimised for 4.7 T, this provides dramatically increased quality and resolution over a large brain volume. Using the array coil, a SNR improvement relative to the volume coil of 1-1.5 times in central brain areas and 2-3 times in cortical regions was obtained. Array coil images with a resolution of 352 x 352 x 2000 mum had a SNR of 16.0 to 26.2 in central regions and 19.9 to 34.8 in cortical areas. Such images easily demonstrate cortical myeloarchitecture, while still covering most of the brain in a approximately 12 min scan.  相似文献   

16.
The 3D geometry of the RF coil in use is often unavailable when the RF coil is a commercial one or the RF coil has been developed through ad hoc modification of the coil shape at the laboratory. Without the coil geometry information, making a 3D model of the RF coil may be necessary to simulate the RF coil performance using a finite difference time domain (FDTD) solver. We used a stylus‐type 3D tracker to measure the 3D positions of the landmarks on the coil wires. From the measured landmark positions, we built 3D models of the coil wires using a 3D design tool. We also carried out FDTD simulation of the RF coil performances after transferring the 3D model data to the FDTD solver. For demonstration, we built 3D models of a shoulder coil and a 36‐channel helmet‐style array coil, and we computed B1 field maps of the coils using the FDTD solver. We think the proposed method can be greatly used for FDTD simulation of the RF coils in use whose geometries are unknown. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 43B: 126–132, 2013  相似文献   

17.
In magnetic induction tomography reducing the influence of the primary excitation field on the sensors can provide a significant improvement in SNR and/or allow the operating frequency to be reduced. For the purposes of imaging, it would be valuable if all, or a useful subset, of the detection coils could be rendered insensitive to the primary field for any excitation coil activated. Suitable schemes which have been previously suggested include the use of axial gradiometers and coil-orientation methods (Bx sensors). This paper examines the relative performance of each method through computer simulation of the sensitivity profiles produced by a single sensor, and comparison of reconstructed images produced by sensor arrays. A finite-difference model was used to determine the sensitivity profiles obtained with each type of sensor arrangement. The modelled volume was a cuboid of dimensions 50 cmx50 cmx12 cm with a uniform conductivity of 1 S m-1. The excitation coils were of 5 cm diameter and the detection coils of 5 mm diameter. The Bx sensors provided greater sensitivity than the axial gradiometers at all depths, other than on the surface layer of the volume. Images produced using a single-planar array were found to contain distortion which was reduced by the addition of a second array.  相似文献   

18.
In most clinical magnetic resonance imaging systems, only commercial receive coils with the appropriate connector and encoding can be plugged in. When willing to use a dedicated receive coil for a specific study which cannot be achieved with commercial coils, the researcher faces the connecting issue related to the specificity of the proprietary connector. In this work, a universal device is proposed which allows for the connection of any single channel dedicated coil on any magnetic resonance (MR) system, as long as it is provided with at least one commercial receive coil. Technical feasibility of the universal connecting device was demonstrated on a 3 T MR clinical imager. The device included an independent active decoupling circuit while signal transmission to the data cabinet was achieved by electromagnetic coupling with a commercial receive coil plugged to the MR device. The universal connecting device was notably characterized in terms of signal‐to‐noise ratio (SNR) and compared to the standard connection. Image SNR was comparable using both means of connection. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 125–133, 2015  相似文献   

19.
An 8-channel receive coil array was constructed and implanted adjacent to the skull in a male rhesus monkey in order to improve the sensitivity of (functional) brain imaging. The permanent implant was part of an acrylic headpost assembly and only the coil element loop wires were implanted. The tuning, matching, and preamplifier circuitry was connected via a removable external assembly. Signal-to-noise ratio (SNR) and noise amplification for parallel imaging were compared to single-, 4-, and 8-channel external receive-only coils routinely used for macaque fMRI. In vivo measurements showed significantly improved SNR within the brain for the implanted versus the external coils. Within a region-of-interest covering the cerebral cortex, we observed a 5.4-, 3.6-fold, and 3.4-fold increase in SNR compared to the external single-, 4-, and 8-channel coils, respectively. In the center of the brain, the implanted array maintained a 2.4×, 2.5×, and 2.1× higher SNR, respectively compared to the external coils. The array performance was evaluated for anatomical, diffusion tensor and functional brain imaging. This study suggests that a stable implanted phased-array coil can be used in macaque MRI to substantially increase the spatial resolution for anatomical, diffusion tensor, and functional imaging.  相似文献   

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