Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany.
Magn Reson Med. 2012 Feb;67(2):300-9. doi: 10.1002/mrm.23018. Epub 2011 Jun 30.
Parallel excitation is being studied intensively for applications in MR imaging and in particular for selecting arbitrary shapes as regions of interest. In this work, parallel excitation was applied to arbitrarily shaped voxel selection in spectroscopy and investigated for different excitation k-space trajectories (radial, rectilinear, and spiral) and acceleration factors. Each trajectory was segmented into multiple excitations to increase the overall bandwidth during target selection. Acceleration by parallel excitation was used to decrease the number of segments. Evaluation of spatial and spectral localization of the target of interest was performed in simulation and phantom experiments, and was compared with the point resolved spectroscopy (PRESS) experiment with standard voxels. The selective excitation experiments demonstrated excellent spatial localization and a broad frequency response, although PRESS was superior in direct comparisons with respect to signal-to-noise ratio (SNR) and outer volume suppression. Extensive SNR variation was observed dependent on trajectory (8%-90%), with the preferred radial case producing approximately 40%-60% SNR of the PRESS case. Accelerated trajectories at R = 4 provided comparable artifact signal and target excitation accuracy compared with their nonaccelerated counterparts; however, further acceleration (R = 8) resulted in increased artifact (33% increase at R = 8).
并行激发在磁共振成像中的应用研究十分活跃，特别是在选择任意形状的感兴趣区域方面。在这项工作中，并行激发被应用于光谱学中任意形状的体素选择，并研究了不同的激发 k 空间轨迹（径向、直线和螺旋）和加速因子。每条轨迹都被分成多个激发，以在目标选择期间增加整体带宽。通过并行激发来加速减少段数。在模拟和体模实验中对感兴趣的目标的空间和光谱定位进行了评估，并与使用标准体素的点分辨光谱（PRESS）实验进行了比较。选择性激发实验表现出极好的空间定位和宽的频率响应，尽管在信噪比（SNR）和外部体积抑制方面，PRESS 直接比较具有优势。观察到轨迹依赖性的 SNR 广泛变化（8％-90％），优选的径向情况产生的 SNR 约为 PRESS 情况的 40％-60％。在 R = 4 处加速轨迹与非加速轨迹相比提供了可比的伪影信号和目标激发精度；然而，进一步的加速（R = 8）导致了伪影的增加（在 R = 8 时增加了 33％）。
