Galiana Gigi, Peters Dana, Tam Leo, Constable R Todd
Yale University, Department of Diagnostic Radiology, Biomedical Engineering, Neurosurgery, New Haven, Connecticut, USA.
Magn Reson Med. 2014 Dec;72(6):1648-57. doi: 10.1002/mrm.25085. Epub 2014 Jan 23.
Nonlinear gradient encoding methods, such as O-Space imaging, have been shown to provide good images from very few echoes. Acquiring data in a train of spin or gradient echoes is a very flexible way to further speed acquisition time. However, combining these strategies presents significant challenges, both in terms of the contrast and artifacts. We present strategies in both pulse sequence design and image processing to mitigate these effects.
The three strategies include a new echo ordering that takes into account the unique way that O-Space samples the k-space of the image; a new postprocessing filter that allows tuning of T2-weighting by emphasizing the contribution of low frequency spatial information at selectable points in space and time; and an offset between linear and nonlinear gradients that makes the central point of each echo unique.
Simulations indicate that these strategies mitigate artifacts introduced by T2 (or T2*) decay and produce contrast that reflects relaxation at a given echo time.
Turbo spin echo O-Space is theoretically feasible, and the greater undersampling should make it possible to use shorter echo trains for a given scan time.
非线性梯度编码方法，如O空间成像，已被证明能从极少的回波中提供良好的图像。在一系列自旋或梯度回波中采集数据是进一步加快采集时间的非常灵活的方式。然而，将这些策略结合起来在对比度和伪影方面都带来了重大挑战。我们在脉冲序列设计和图像处理方面都提出了策略来减轻这些影响。
这三种策略包括一种新的回波排序，它考虑了O空间对图像k空间进行采样的独特方式；一种新的后处理滤波器，通过在空间和时间的可选点强调低频空间信息的贡献来实现对T2加权的调整；以及线性和非线性梯度之间的偏移，使每个回波的中心点具有唯一性。
模拟表明，这些策略减轻了由T2（或T2*）衰减引入的伪影，并产生了反映给定回波时间弛豫的对比度。
快速自旋回波O空间在理论上是可行的，更大程度的欠采样应该使得在给定扫描时间内使用更短的回波链成为可能。
