Correction of gradient echo images for first and second order macroscopic signal dephasing using phase derivative mapping
Correction of gradient echo images for first and second order macroscopic signal dephasing using phase derivative mapping
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DOI：
10.1016/j.neuroimage.2011.11.083
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发表时间：
2012-03-01
期刊：
影响因子：
5.7
通讯作者：
Bakker, C. J. G.
中科院分区：
文献类型：
--
作者：
de Leeuw, H.;Bakker, C. J. G.
由于系统缺陷（匀场）或物体引起的磁场扰动（出血性病变、钙化组织、空气-组织界面），导致宏观相位扰动，梯度回波技术经常受到信号相移的阻碍。已经提出了许多技术来减少宏观相位变化的影响。这些技术包括调谐脉冲序列、拟合技术和重建算法。然而，这些方法存在以下一个或多个缺点：它们需要较长的采集时间、需要额外的采集、仅在本地进行补偿、只能应用于多梯度回波数据或可能导致不准确的结果。在这项工作中，提出了一种普遍适用的后处理技术来评估和补偿由一阶和二阶宏观相位不相干引起的信号改变。在该技术中，通过对复数数据应用傅立叶导数定理来确定信号相位的导数。因此，无需相位展开且不会影响分辨率即可获得相位导数。通过在具有已知宏观场扰动的同轴圆柱体模型上进行实验，对该方法进行了单回波和多回波采集的验证。该方法的潜力在人类志愿者头部的多梯度回波采集中得到了证明。一般来说，一阶校正被证明是足够的，然而，发现更高阶校正在磁场的急剧转变附近是有益的。 (C) 2011 Elsevier Inc. 保留所有权利。
Gradient echo techniques are often hampered by signal dephasing due to macroscopic phase perturbations because of system imperfections (shimming) or object induced perturbations of the magnetic field (hemorrhagic lesions, calcified tissue, air-tissue interfaces). Many techniques have been proposed to reduce the effects of macroscopic phase variations. Among these techniques are tuned pulse sequences, fitting techniques and reconstruction algorithms. These methods, however, suffer from one or more of the following draw-backs: they require longer acquisition times, require additional acquisitions, compensate only locally, can only be applied to multi-gradient echo data or may result in inaccurate results.In this work a generally applicable post-processing technique is presented to evaluate and compensate signal alterations invoked by first and second order macroscopic phase incoherences. In this technique, the derivatives of the signal phase are determined by applying the Fourier derivative theorem on the complex data. As a result, the phase derivatives are obtained without phase unwrapping and without compromising the resolution. The method is validated for single and multi-echo acquisitions by experiments on a co-axial cylinder phantom with known macroscopic field disturbances. The potential of the method is demonstrated on a multi-gradient echo acquisition on the head of a human volunteer. In general a first order correction is shown to be sufficient, however higher order correction is found to be beneficial near sharp transitions of the magnetic field. (C) 2011 Elsevier Inc. All rights reserved.