Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Magn Reson Med. 2012 Nov;68(5):1383-9. doi: 10.1002/mrm.24172. Epub 2012 Jan 31.
Recently, spatially two-dimensional selective radiofrequency excitations based on the PROPELLER trajectory have been presented and were applied to minimize partial volume effects in single-voxel MR spectroscopy. Thereby, residual side excitations appeared due to limitations of the Voronoi diagram that was used to consider the nonconstant sampling density, and trajectory distortions caused by eddy currents varying between the differently rotated blades. In this extension, one of the refocusing radiofrequency pulses of a PRESS-based pulse sequence is applied in the blip direction of each segment to eliminate the side excitations. This corresponds to an infinitely dense sampling of the blade and the required sampling density correction can easily be calculated. Thus, signal contributions from outside the desired region-of-interest are completely avoided. The feasibility of this approach to acquire single-voxel MR spectra of anatomically defined regions-of-interest is demonstrated in the human brain in vivo on a 3T whole-body MR system.
最近，基于 PROPELLER 轨迹的空间二维选择性射频激发被提出，并被应用于最小化单体磁共振波谱中的部分容积效应。由此，由于 Voronoi 图的限制，出现了残留的旁侧激发，Voronoi 图用于考虑非恒定采样密度，而涡流引起的轨迹变形则发生在不同旋转叶片之间。在这个扩展中，一种基于 PRESS 的脉冲序列的重聚焦射频脉冲被应用于每个段的闪烁方向，以消除旁侧激发。这对应于叶片的无限密集采样，并且可以轻松计算所需的采样密度校正。因此，完全避免了来自期望的感兴趣区域之外的信号贡献。在 3T 全身磁共振系统上对人体大脑进行的体内实验证明了这种获取解剖定义的感兴趣区域的单体磁共振波谱的方法的可行性。
