Wild Jim M, Paley Martyn N J, Viallon Magalie, Schreiber Wolfgang G, van Beek Edwin J R, Griffiths Paul D
Section of Academic Radiology, Royal Hallamshirw Hospital, University of Sheffield, Sheffield, UK.
Magn Reson Med. 2002 Apr;47(4):687-95. doi: 10.1002/mrm.10134.
In this work some of the factors that can influence the signal-to-noise ratio (SNR) and spatial resolution in MR images of inhaled hyperpolarized gases are systematically addressed. In particular, the effects of RF depletion of longitudinal polarization and image gradient diffusion dephasing were assessed in terms of their contribution to a k-space filter. By means of theoretical simulations and a novel method of experimental validation using a variable transverse magnetization of the 1H signal, systematic quantitative and qualitative investigations of the effects of k-space filtering intrinsic to imaging of hyperpolarized gas were made. A 2D gradient-echo image is considered for a range of flip angles with centric, sequential, and half-Fourier Cartesian phase-encoding strategies, and the results are assessed in terms of SNR and spatial resolution in the reconstructed images. Centric phase encoding was found to give the best SNR at higher flip angles, with a trade-off in spatial resolution compared to sequential phase encoding. A half-Fourier approach potentially offers increased SNR through the use of higher flip angles without compromising the spatial resolution, which is comparable to that achieved with sequential encoding.
在这项工作中，系统地探讨了一些可能影响吸入超极化气体的磁共振图像中信噪比（SNR）和空间分辨率的因素。特别是，从纵向极化的射频损耗和图像梯度扩散去相移对k空间滤波器的贡献方面评估了它们的影响。通过理论模拟和一种使用1H信号可变横向磁化的新型实验验证方法，对超极化气体成像固有的k空间滤波效应进行了系统的定量和定性研究。对于一系列具有中心、顺序和半傅里叶笛卡尔相位编码策略的翻转角，考虑了二维梯度回波图像，并根据重建图像中的SNR和空间分辨率对结果进行了评估。发现在较高翻转角下，中心相位编码能给出最佳的SNR，但与顺序相位编码相比，在空间分辨率上有所权衡。半傅里叶方法通过使用更高的翻转角有可能提高SNR，同时不影响空间分辨率，其空间分辨率与顺序编码所达到的相当。
