Optimization and validation of methods for mapping of the radiofrequency transmit field at 3T.
Optimization and validation of methods for mapping of the radiofrequency transmit field at 3T.
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DOI：
10.1002/mrm.22421
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发表时间：
2010-07
影响因子：
3.3
通讯作者：
Weiskopf, Nikolaus
中科院分区：
文献类型：
--
作者：
Lutti, Antoine;Hutton, Chloe;Finsterbusch, Juergen;Helms, Gunther;Weiskopf, Nikolaus
定量成像和并行发射等MRI技术需要精确了解射频发射场（）。优化了三种已发表的方法，用于在人脑中进行3 T下的稳健标测：三维（3D）实际翻转角成像（AFI）、3D回波平面成像（EPI）和二维（2D）受激回波采集模式（STEAM）。我们对这些方法进行了全面比较，重点是与参考2D双角度方法相比的伪影、再现性和准确性。对于3D AFI方法，增加用于扩散阻尼的流量补偿梯度降低了生理伪影的水平，并改善了横向相干性的破坏。校正可磁化率引起的伪影减轻了图像失真，提高了3D EPI成像方法的准确性。对于2D STEAM方法，多次采集的平均值降低了生理噪声的影响，新的校准方法提高了标测图的准确性。优化后，所有方法都产生了低噪声图（低于2个百分比单位），标称翻转角值（p.u.）系统偏差小于5 p.u.单位在不到5分钟的时间内获得全脑覆盖。3D AFI方法需要最少的后处理，对非共振和生理效应的敏感性很小。3D EPI方法显示出最高水平的再现性。2D STEAM方法是最省时的技术。Magn Reson Med，2010年。© 2010 Wiley-Liss公司。
MRI techniques such as quantitative imaging and parallel transmit require precise knowledge of the radio-frequency transmit field (). Three published methods were optimized for robust mapping at 3T in the human brain: three-dimensional (3D) actual flip angle imaging (AFI), 3D echo-planar imaging (EPI), and two-dimensional (2D) stimulated echo acquisition mode (STEAM). We performed a comprehensive comparison of the methods, focusing on artifacts, reproducibility, and accuracy compared to a reference 2D double angle method. For the 3D AFI method, the addition of flow-compensated gradients for diffusion damping reduced the level of physiological artifacts and improved spoiling of transverse coherences. Correction of susceptibility-induced artifacts alleviated image distortions and improved the accuracy of the 3D EPI imaging method. For the 2D STEAM method, averaging over multiple acquisitions reduced the impact of physiological noise and a new calibration method enhanced the accuracy of the maps. After optimization, all methods yielded low noise maps (below 2 percentage units), of the nominal flip angle value (p.u.) with a systematic bias less than 5 p.u. units. Full brain coverage was obtained in less than 5 min. The 3D AFI method required minimal postprocessing and showed little sensitivity to off-resonance and physiological effects. The 3D EPI method showed the highest level of reproducibility. The 2D STEAM method was the most time-efficient technique. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.
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