Strategies for inner volume 3D fast spin echo magnetic resonance imaging using nonselective refocusing radio frequency pulses
Strategies for inner volume 3D fast spin echo magnetic resonance imaging using nonselective refocusing radio frequency pulses
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DOI：
10.1118/1.2148331
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发表时间：
2006-01-01
期刊：
影响因子：
3.8
通讯作者：
Rybicki, FJ
中科院分区：
文献类型：
--
作者：
Mitsouras, D;Mulkern, RV;Rybicki, FJ
已经提出了由非选择性“硬”重聚焦射频（RF）脉冲引起的快速自旋回波（FSE）串作为使得能够将FSE方法应用于高分辨率3D磁共振成像（MRI）的手段。硬脉冲FSE（HPFSE）序列提供短（3-4 ms）回波间隔，但不幸的是，仅限于在线圈灵敏度内对整个样本进行成像，因此需要较长的成像时间，从而限制了临床应用。在这项工作中，我们制定和分析两个通用的组合，三维HPFSE与内部容积（IV）的MR成像，以规避这一限制。第一种方法采用2D选择性RF激励，然后是HPFSE序列，并侧重于空间激励分布的所需特性，以将RF脉冲持续时间限制在5-6 ms范围内。第二种方法采用两个正交选择的1D RF激励（90（x）度-180（y）度对），以从由它们的交叉点限定的体积内的磁化产生回波。随后的回波通过HPFSE序列形成，将该方法的重点放在（a）避免杂散回波和（B）避免由于RF脉冲施加的必然不同的间隔（在时间上）而引起的信号损失上，其中杂散回波可能在板交叉点外部的横向磁化受到非选择性重聚焦脉冲的影响时由横向磁化引起。使用Carr-Purcell-Meiboom-Gill（CPMG）多回波成像实验测量每种方法的性能，从而检查整个回波链的磁化演变。所实施的方法实现了95%至97%的外部体积信号抑制，并且通过选择性RF激励的进一步细化，更高的抑制似乎是完全可以达到的。每种技术都提供了人脑和脊柱的示例图像。我们得出结论，体积成像的SNR效率与硬脉冲串提供的短回波间隔相结合，使高分辨率3D HPFSE MRI的小视场（FOV），最小的混叠伪影。(c)2006年美国医学物理学家协会B。
Fast spin echo (FSE) trains elicited by nonselective "hard" refocusing radio frequency (RF) pulses have been proposed as a means to enable application of FSE methods for high-resolution 3D magnetic resonance imaging (MRI). Hard-pulse FSE (HPFSE) trains offer short (3-4 ms) echo spacings, but are unfortunately limited to imaging the entire sample within the coil sensitivity thus requiring lengthy imaging times, consequently limiting clinical application. In this work we formulate and analyze two general-purpose combinations of 3D HPFSE with inner volume (IV) MR imaging to circumvent this limitation. The first method employs a 2D selective RF excitation followed by the HPFSE train and focuses on required properties of the spatial excitation profile with respect to limiting RF pulse duration in the 5-6 ms range. The second method employs two orthogonally selective 1D RF excitations (a 90(x)degrees- 180(y)degrees pair) to generate an echo from magnetization within the volume defined by their intersection. Subsequent echoes are formed via the HPFSE train, placing the focus of the method on (a) avoiding spurious echoes that may arise from transverse magnetization located outside the slab intersection when it is unavoidably affected by the nonselective refocusing pulses and (b) avoiding signal losses due to the necessarily different spacing (in time) of the RF pulse applications. The performance of each method is experimentally measured using Carr-Purcell-Meiboom-Gill (CPMG) multi-echo imaging, enabling examination of the magnetization evolution throughout the echo train. The methods as implemented achieve 95% to 97% outer volume signal suppression, and higher suppression appears to be well within reach, by further refinement of the selective RF excitations. Example images of the human brain and spine are presented with each technique. We conclude that the SNR efficiency of volume imaging in conjunction with the short echo spacing afforded by hard pulse trains enables high-resolution 3D HPFSE MRI of a small field-of-view (FOV) with minimal aliasing artifact. (c) 2006 American b Association of Physicists in Medicine.