Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
Magn Reson Med. 2012 Dec;68(6):1755-63. doi: 10.1002/mrm.24506. Epub 2012 Sep 24.
In this work, diffusion weighting and parallel imaging is combined with a vertical gradient and spin echo data readout. This sequence was implemented and evaluated on healthy volunteers using a 1.5 and a 3 T whole-body MR system. As the vertical gradient and spin echo trajectory enables a higher k-space velocity in the phase-encoding direction than single-shot echo planar imaging, the geometrical distortions are reduced. When combined with parallel imaging such as generalized autocalibrating partially parallel acquisition, the geometric distortions are reduced even further, while also keeping the minimum echo time reasonably low. However, this combination of a diffusion preparation and multiple refocusing pulses during the vertical gradient and spin echo readout, generally violates the Carr-Purcell-Meiboom-Gill condition, which leads to interferences between echo pathways. To suppress the stimulated echo pathway, refocusing pulses with a sharper slice profiles and an odd/even crusher variation scheme were implemented and evaluated. Being a single-shot acquisition technique, the reconstructed images are robust to rigid-body head motion and spatially varying brain motion, both of which are common sources of artifacts in diffusion MRI.
在这项工作中，扩散加权和并行成像与垂直梯度和自旋回波数据读出相结合。该序列已在健康志愿者中使用 1.5T 和 3T 全身磁共振系统进行了实施和评估。由于垂直梯度和自旋回波轨迹使相位编码方向上的 k 空间速度高于单次回波平面成像，因此可以减少几何变形。当与并行成像（如广义自校准部分并行采集）结合使用时，即使保持最小回波时间相当低，也可以进一步减少几何变形。然而，这种扩散准备和多个重聚焦脉冲在垂直梯度和自旋回波读出过程中的组合通常会违反 Carr-Purcell-Meiboom-Gill 条件，从而导致回波路径之间的干扰。为了抑制受激回波路径，实施并评估了具有更陡峭的切片轮廓和奇数/偶数破碎机变化方案的重聚焦脉冲。作为单次采集技术，重建图像对刚体头部运动和空间变化的大脑运动具有鲁棒性，这两者都是扩散 MRI 中伪影的常见来源。
