Direct parallel image reconstructions for spiral trajectories using GRAPPA
Direct parallel image reconstructions for spiral trajectories using GRAPPA
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DOI：
10.1002/mrm.20951
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发表时间：
2006-08-01
影响因子：
3.3
通讯作者：
Jakob, Peter M.
中科院分区：
文献类型：
--
作者：
Heidemann, Robin M.;Griswold, Mark A.;Jakob, Peter M.
在磁共振成像（MRI）中，螺旋轨迹的使用是覆盖所需k空间分区的有效方法。与传统的笛卡尔k空间采样相比，它允许更快的采集，并在快速动态扫描（如功能MRI (fMRI)）中略微减少高梯度需求。然而，螺旋图像更容易受到非共振效应的影响，从而导致模糊的伪影和点扩散函数（PSF）的扭曲，从而降低图像质量。由于非共振效应与读出持续时间有关，因此可以通过缩短读出轨迹来减少相应的伪影。多镜头实验是减少螺旋成像中这些伪影的一种方法，但会导致扫描时间更长，并可能增加流动和运动伪影。并行成像方法是通过提高采集速度来提高图像质量的另一种有前途的方法。然而，非笛卡尔平行图像重建被认为是计算耗时，这是禁止临床应用。本文提出了一种基于广义自校准部分平行采集（GRAPPA）方法的螺旋成像快速并行图像重建新方法。通过这种方法，计算负担减少了，使其与加速笛卡尔过程所需的计算量相当。具有2到8倍加速度的螺旋图像显然受益于并行成像的优势，例如实现了并行MRI单次螺旋成像与多次采集的非共振行为。
The use of spiral trajectories is an efficient way to cover a desired k-space partition in magnetic resonance imaging (MRI). Compared to conventional Cartesian k-space sampling, it allows faster acquisitions and results in a slight reduction of the high gradient demand in fast dynamic scans, such as in functional MRI (fMRI). However, spiral images are more susceptible to off-resonance effects that cause blurring artifacts and distortions of the point-spread function (PSF), and thereby degrade the image quality. Since off-resonance effects scale with the readout duration, the respective artifacts can be reduced by shortening the readout trajectory. Multishot experiments represent one approach to reduce these artifacts in spiral imaging, but result in longer scan times and potentially increased flow and motion artifacts. Parallel imaging methods are another promising approach to improve image quality through an increase in the acquisition speed. However, non-Cartesian parallel image reconstructions are known to be computationally time-consuming, which is prohibitive for clinical applications. In this study a new and fast approach for parallel image reconstructions for spiral imaging based on the generalized autocalibrating partially parallel acquisitions (GRAPPA) methodology is presented. With this approach the computational burden is reduced such that it becomes comparable to that needed in accelerated Cartesian procedures. The respective spiral images with two- to eightfold acceleration clearly benefit from the advantages of parallel imaging, such as enabling parallel MRI single-shot spiral imaging with the off-resonance behavior of multishot acquisitions.