PexLoc-Parallel Excitation Using Local Encoding Magnetic Fields with Nonlinear and Nonbijective Spatial Profiles
PexLoc-Parallel Excitation Using Local Encoding Magnetic Fields with Nonlinear and Nonbijective Spatial Profiles
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DOI：
10.1002/mrm.24559
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发表时间：
2013-11-01
影响因子：
3.3
通讯作者：
Zaitsev, M.
中科院分区：
文献类型：
--
作者：
Haas, M.;Ullmann, P.;Zaitsev, M.
随着最近提出的使用通过空间编码设计为非线性的磁场，新的灵活性已经被引入到MR成像中。在对空间编码磁场（SEM）进行成形时的新的自由度可以用于使成像分辨率局部地适应于成像对象的特征，例如，在一些实施例中，梯度切换可以通过改变解剖结构来实现，以减少体内实验期间的外周神经刺激，或者通过减少产生SEM的线圈的电感来增加梯度切换速度，从而加速成像过程。在这项工作中，潜在的非线性和非双射SEM的空间编码在多维空间选择性激发传输过程中进行了探索。介绍了基于非线性编码场的多维空间选择性激励射频脉冲设计方法，并展示了如何使用并行传输解决编码模糊性。在模拟和幻影实验中，使用非线性，非双射SEM的选择性激励的可行性被证明，它示出的横向磁化的目标分布可以实现的空间分辨率局部变化。因此，与传统的线性编码相比，可以在某些区域中提高目标图案的分辨率。此外，实验证明的原理，加速二维空间选择性激发使用非线性SEM在这项研究中提供。Magn Reson Med 70：1220-1228，2013. (c)2012 Wiley Periodicals，Inc.
With the recent proposal of using magnetic fields that are nonlinear by design for spatial encoding, new flexibility has been introduced to MR imaging. The new degrees of freedom in shaping the spatially encoding magnetic fields (SEMs) can be used to locally adapt the imaging resolution to features of the imaged object, e.g., anatomical structures, to reduce peripheral nerve stimulation during in vivo experiments or to increase the gradient switching speed by reducing the inductance of the coils producing the SEMs and thus accelerate the imaging process. In this work, the potential of nonlinear and nonbijective SEMs for spatial encoding during transmission in multidimensional spatially selective excitation is explored. Methods for multidimensional spatially selective excitation radiofrequency pulse design based on nonlinear encoding fields are introduced, and it is shown how encoding ambiguities can be resolved using parallel transmission. In simulations and phantom experiments, the feasibility of selective excitation using nonlinear, nonbijective SEMs is demonstrated, and it is shown that the spatial resolution with which the target distribution of the transverse magnetization can be realized varies locally. Thus, the resolution of the target pattern can be increased in some regions compared with conventional linear encoding. Furthermore, experimental proof of principle of accelerated two-dimensional spatially selective excitation using nonlinear SEMs is provided in this study. Magn Reson Med 70:1220-1228, 2013. (c) 2012 Wiley Periodicals, Inc.