Wyatt Cory R, Guimaraes Alexander R
Department of Diagnostic Radiology, Oregon Health & Sciences University, Portland, Oregon, USA.
Advanced Imaging Research Center, Oregon Health & Sciences University, Portland, Oregon, USA.
Magn Reson Med. 2022 Jul;88(1):151-163. doi: 10.1002/mrm.29197. Epub 2022 Mar 24.
Seiffert spirals were recently explored as an efficient way to traverse 3D k-space compared to traditional 3D techniques. Several studies have shown the ability of 3D MR fingerprinting (MRF) techniques to acquire T and T relaxation maps in a short period of time. However, these sequences do not sample across a large region of 3D k-space every TR, especially in the way that Seiffert trajectories can.
A 3D MRF sequence was designed using 8 Seiffert spirals rotated in 3D k-space, with flip angle modulation for T and T sensitivity. The sequence was compared to an MRF sequence using a 2D spiral rotated in 3D k-space using the tiny golden angle acquisition with similar resolution/readout duration. Both sequences were evaluated using simulations, phantom validation, and in vivo imaging.
In all experiments, the Seiffert spiral MRF sequence performed similar to if not better than the multi-axis 2D spiral MRF sequence. Strong intraclass correlation coefficients (> 0.9) were found between conventional and MRF sequences in phantoms, whereas the in vivo results showed slightly less aliasing artifact with the Seiffert trajectory.
In this study, Seiffert spirals were used within the MRF framework to acquire high-resolution T and T relaxation time maps in less than 2.5 min. The reduced aliasing artifacts seen with the Seiffert sequence suggests that sampling over 3D k-space evenly each TR can improve quantification or shorten scan times.
与传统的3D技术相比，最近人们探索了赛弗特螺旋作为一种遍历3D k空间的有效方法。多项研究表明，3D磁共振指纹识别（MRF）技术能够在短时间内获取T1和T2弛豫图。然而，这些序列并非每个重复时间（TR）都对3D k空间的大片区域进行采样，尤其是不像赛弗特轨迹那样进行采样。
设计了一种3D MRF序列，该序列使用在3D k空间中旋转的8个赛弗特螺旋，并对翻转角进行调制以实现T1和T2灵敏度。将该序列与使用在3D k空间中旋转的2D螺旋并采用微小黄金角采集且具有相似分辨率/读出持续时间的MRF序列进行比较。使用模拟、体模验证和活体成像对这两种序列进行评估。
在所有实验中，赛弗特螺旋MRF序列的表现即便不比多轴2D螺旋MRF序列更好，也与之相似。在体模中，传统序列和MRF序列之间发现了很强的组内相关系数（>0.9），而活体成像结果显示，赛弗特轨迹产生的混叠伪影略少。
在本研究中，赛弗特螺旋被用于MRF框架内，以在不到2.5分钟的时间内获取高分辨率的T1和T2弛豫时间图。赛弗特序列中观察到的混叠伪影减少表明，每个TR均匀地对3D k空间进行采样可以改善定量分析或缩短扫描时间。
