State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, and Graduate University, Chinese Academy of Sciences, Beijing, People's Republic of China.
Neuroimage. 2010 Jan 1;49(1):457-66. doi: 10.1016/j.neuroimage.2009.07.044. Epub 2009 Jul 28.
For more than a decade, turbo spin echo (TSE) pulse sequences have been suggested as an alternative to echo planar imaging (EPI) sequences for fMRI studies. Recent development in parallel imaging has renewed the interest in developing more robust TSE sequences for fMRI. In this study, a modified half Fourier acquisition single-shot TSE (mHASTE) sequence has been developed with a three-fold GRAPPA to improve temporal resolution as well as a preparation time to enhance BOLD sensitivity. Using a classical flashing checkerboard block design, the BOLD signal characteristics of this novel method have been systematically analyzed as a function of several sequence parameters and compared to those of gradient-echo and spin-echo EPI sequences. Experimental studies on visual cortex of five volunteers have provided evidence suggesting that mHASTE can be more sensitive to extra-vascular BOLD effects around microvascular networks, which leads to more accurate function localization. The studies also show that the activation cluster size in mHASTE increases with the refocusing RF flip angle and TE while decreasing with the echo number (n(center)) used to sample the k-space center. Compared to spin-echo EPI, mHASTE incurs an approximately 50% reduction in activation cluster size and an approximately 20% decrease in BOLD contrast. However a higher signal-to-noise ratio and a spatially more uniform temporal stability have been observed in mHASTE as compared to the EPI sequences when the scan times are held constant. With further refinement and optimization, mHASTE can become a viable alternative for fMRI in situations where the conventional EPI sequences are limited or prohibitive.
十多来，涡轮自旋回波（TSE）脉冲序列已被提议作为 fMRI 研究中替代回波平面成像（EPI）序列的方法。并行成像技术的最新发展重新激发了为 fMRI 开发更强大的 TSE 序列的兴趣。在这项研究中，开发了一种改进的半傅里叶采集单次激发 TSE（mHASTE）序列，采用三重 GRAPPA 提高时间分辨率和准备时间以增强 BOLD 灵敏度。使用经典闪烁棋盘块设计，系统地分析了该新方法的 BOLD 信号特征作为几个序列参数的函数，并与梯度回波和自旋回波 EPI 序列进行了比较。在五名志愿者的视觉皮层的实验研究提供了证据，表明 mHASTE 可以更敏感地检测到微血管周围的血管外 BOLD 效应，从而更准确地定位功能。研究还表明，mHASTE 中的激活簇大小随重聚焦 RF 翻转角和 TE 增加而增加，而随用于采样 k 空间中心的回波数（n(center)) 减少而减少。与自旋回波 EPI 相比，mHASTE 的激活簇大小减少约 50%，BOLD 对比度降低约 20%。然而，当扫描时间保持不变时，与 EPI 序列相比，mHASTE 具有更高的信噪比和空间更均匀的时间稳定性。随着进一步的改进和优化，mHASTE 可以成为传统 EPI 序列有限或不可行情况下 fMRI 的可行替代方法。
