Paley Martyn N J, Wild James M, Lee Kuan J, Griffiths Paul D, Whitby Elspeth H
Academic Radiology, University of Sheffield, Royal Hallamshire Hospital, Sheffield, UK.
Magn Reson Imaging. 2007 Dec;25(10):1402-8. doi: 10.1016/j.mri.2007.03.033. Epub 2007 Jun 13.
A method of determining the phase-encode order for MR Fourier-encoded imaging is described, which provides an additional option for optimizing images from samples with signals that change during data acquisition. Examples are in hyperpolarized helium gas imaging of the lungs where polarization is lost with each RF pulse or the signal changes observed in rapid dynamic studies with T(1) or T(2)* contrast agents when mixing is taking place. The method uses a single frequency-encoded projection in the proposed phase-encoding direction. The projection is subsequently sorted into signal-to-noise ratio (SNR) order. The indices of the sorted array are then used to create the phase-encode table to be used for the scan. This phase table is sorted in descending SNR order for signals that decrease during data acquisition and in ascending order for signals that increase during data acquisition. Simulations suggest that this technique can produce higher resolution than centric-ordered phase encoding at the expense of increased modulation (ghosting) artifact for dynamically changing signals. Initial practical implementation of the technique has been carried out on a dedicated 0.2-T Niche MR system, and the test object results agree well with simulations. Hyperpolarized 3-He lung images have also been acquired and postprocessed using the SNR phase order k-space encoding (SPOKE) methodology and show potential for improved imaging with high flip angles where polarization is rapidly lost. Applications may also be found for 3D volumetric acquisitions where two dimensions can be SPOKE encoded.
描述了一种用于磁共振傅里叶编码成像确定相位编码顺序的方法，该方法为优化来自在数据采集期间信号发生变化的样本的图像提供了额外选项。例如在肺部的超极化氦气成像中，每次射频脉冲都会导致极化丧失，或者在使用T(1)或T(2)*造影剂的快速动态研究中，当发生混合时会观察到信号变化。该方法在所提议的相位编码方向上使用单个频率编码投影。随后将该投影按信噪比（SNR）顺序排序。然后使用排序后数组的索引来创建用于扫描的相位编码表。对于在数据采集期间信号降低的情况，此相位表按SNR降序排序；对于在数据采集期间信号增加的情况，则按升序排序。模拟表明，对于动态变化的信号，该技术可以产生比中心排序相位编码更高的分辨率，但代价是增加了调制（鬼影）伪影。该技术的初步实际应用已在专用的0.2-T Niche磁共振系统上进行，测试对象的结果与模拟结果非常吻合。还使用信噪比相位顺序k空间编码（SPOKE）方法采集并后处理了超极化3-He肺部图像，结果表明在高翻转角度下，极化迅速丧失时，该方法在改善成像方面具有潜力。对于三维容积采集，其中两个维度可以进行SPOKE编码，也可能会有应用。
