Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.
Magn Reson Med. 2010 Apr;63(4):1015-20. doi: 10.1002/mrm.22283.
In this study, the sensitivity of the S(2)-steady-state free precession (SSFP) signal for functional MRI at 7 T was investigated. In order to achieve the necessary temporal resolution, a three-dimensional acquisition scheme with acceleration along two spatial axes was employed. Activation maps based on S(2)-steady-state free precession data showed similar spatial localization of activation and sensitivity as spin-echo echo-planar imaging (SE-EPI), but data can be acquired with substantially lower power deposition. The functional sensitivity estimated by the average z-values was not significantly different for SE-EPI compared to the S(2)-signal but was slightly lower for the S(2)-signal (6.74 +/- 0.32 for the TR = 15 ms protocol and 7.51 +/- 0.78 for the TR = 27 ms protocol) compared to SE-EPI (7.49 +/- 1.44 and 8.05 +/- 1.67) using the same activated voxels, respectively. The relative signal changes in these voxels upon activation were slightly lower for SE-EPI (2.37% +/- 0.18%) compared to the TR = 15 ms S(2)-SSFP protocol (2.75% +/- 0.53%) and significantly lower than the TR = 27 ms protocol (5.38% +/- 1.28%), in line with simulations results. The large relative signal change for the long TR SSFP protocol can be explained by contributions from multiple coherence pathways and the low intrinsic intensity of the S(2) signal. In conclusion, whole-brain T(2)-weighted functional MRI with negligible image distortion at 7 T is feasible using the S(2)-SSFP sequence and partially parallel imaging.
在这项研究中，我们研究了在 7T 下 S(2)-稳态自由进动（SSFP）信号在功能磁共振成像中的灵敏度。为了达到必要的时间分辨率，采用了一种沿两个空间轴加速的三维采集方案。基于 S(2)-稳态自由进动数据的激活图显示了与自旋回波回波平面成像（SE-EPI）相似的激活和灵敏度的空间定位，但数据采集的功率沉积要低得多。通过平均 z 值估计的功能灵敏度在 SE-EPI 与 S(2)-信号之间没有显著差异，但在 S(2)-信号下略低（TR = 15ms 协议下为 6.74 +/- 0.32，TR = 27ms 协议下为 7.51 +/- 0.78），而 SE-EPI 分别为 7.49 +/- 1.44 和 8.05 +/- 1.67，使用相同的激活体素。在这些体素中，SE-EPI 的相对信号变化略低（2.37% +/- 0.18%），而 TR = 15ms S(2)-SSFP 协议的相对信号变化略高（2.75% +/- 0.53%），明显低于 TR = 27ms 协议（5.38% +/- 1.28%），与模拟结果一致。长 TR SSFP 协议的大相对信号变化可以用多个相干途径的贡献和 S(2)信号的低固有强度来解释。总之，使用 S(2)-SSFP 序列和部分并行成像，在 7T 下进行全脑 T(2)-加权功能磁共振成像，具有可忽略的图像失真，是可行的。
