Bilgic Berkin, Ye Huihui, Wald Lawrence L, Setsompop Kawin
Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA.
State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, Zhejiang, China; Center for Brain Imaging Science and Technology, Key Laboratory for Biomedical Engineering of Ministry of Education, College of Biomedical Engineering & Instrument Science, Zhejiang University, Hangzhou, Zhejiang, China.
Neuroimage. 2017 Jul 15;155:577-586. doi: 10.1016/j.neuroimage.2017.04.036. Epub 2017 Apr 20.
T* weighted 3D Gradient Echo (GRE) acquisition is the main sequence used for Susceptibility Weighted Imaging (SWI) and Quantitative Susceptibility Mapping (QSM). These applications require a long echo time (TE) to build up phase contrast, requiring a long repetition time (TR), and leading to excessively lengthy scans. The long TE acquisition creates a significant amount of unused time within each TR, which can be utilized for either multi-echo sampling or additional image encoding with the echo-shift technique. The latter leads to significant saving in acquisition time while retaining the desired phase and T* contrast. In this work, we introduce the Simultaneous Time Interleaved MultiSlice (STIMS) echo-shift technique, which mitigates slab boundary artifacts by interleaving comb-shaped slice groups with Simultaneous MultiSlice (SMS) excitation. This enjoys the same SNR benefit of 3D signal averaging as previously introduced multi-slab version, where each slab group is sub-resolved with kz phase encoding. Further, we combine SMS echo-shift with Compressed Sensing (CS) Wave acceleration, which enhances Wave-CAIPI acquisition/reconstruction with random undersampling and sparsity prior. STIMS and CS-Wave combination thus yields up to 45-fold acceleration over conventional full encoding, allowing a 15sec full-brain acquisition with 1.5 mm isotropic resolution at long TE of 39 ms at 3T. In addition to utilizing empty sequence time due to long TE, STIMS is a general concept that could exploit gaps due to e.g. inversion modules in magnetization-prepared rapid gradient-echo (MPRAGE) and fluid attenuated inversion recovery (FLAIR) sequences.
T加权三维梯度回波（GRE）采集是用于磁敏感加权成像（SWI）和定量磁敏感图谱（QSM）的主要序列。这些应用需要较长的回波时间（TE）来建立相位对比度，这就需要较长的重复时间（TR），从而导致扫描时间过长。长TE采集在每个TR内产生大量未使用的时间，这些时间可用于多回波采样或采用回波移位技术进行额外的图像编码。后者在保留所需相位和T对比度的同时，可显著节省采集时间。在这项工作中，我们引入了同步时间交错多层（STIMS）回波移位技术，该技术通过将梳状切片组与同步多层（SMS）激发交错排列来减轻层板边界伪影。这与之前引入的多板版本具有相同的三维信号平均信噪比优势，其中每个板组通过kz相位编码进行子分辨。此外，我们将SMS回波移位与压缩感知（CS）波加速相结合，通过随机欠采样和稀疏先验增强波控阵成像采集/重建。因此，STIMS和CS波的组合比传统的全编码加速高达45倍，在3T场强下，以39 ms的长TE实现1.5毫米各向同性分辨率的15秒全脑采集。除了利用长TE导致的空序列时间外，STIMS是一个通用概念，它可以利用例如磁化准备快速梯度回波（MPRAGE）和液体衰减反转恢复（FLAIR）序列中的反转模块所产生的间隙。
