Cao Peng, Hyder Fahmeed, Zhou Iris Y, Zhang Jevin W, Xie Victor B, Tsang Adrian, Wu Ed X
Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong, SAR, China.
Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong, SAR, China.
NMR Biomed. 2017 Sep;30(9). doi: 10.1002/nbm.3745. Epub 2017 Jun 2.
This study aimed to dissociate the intravascular and extravascular contributions to spin-echo (SE) and gradient-echo (GE) blood oxygenation level-dependent (BOLD) signals at 7 T, using dynamic diffusion-weighted MRS. We simultaneously acquired SE and GE data using a point-resolved spectroscopy sequence with diffusion weightings of 0, 600, and 1200 s/mm . The BOLD signals were quantified by fitting the free induction decays starting from the SE center to a mono-exponential decay function. Without diffusion weighting, BOLD signals measured with SE and GE increased by 1.6 ± 0.5% (TE = 40 ms) and 5.2 ± 1.4% (nominal TE = 40 ms) during stimulation, respectively. With diffusion weighting, the BOLD increase during stimulation measured with SE decreased from 1.6 ± 0.5% to 1.3 ± 0.4% (P < 0.001), whereas that measured by GE was unaffected (P > 0.05); the post-stimulation undershoots in the BOLD signal time courses were largely preserved in both SE and GE measurements. These results demonstrated the feasiblity of simultaneous SE and GE measurements of BOLD signals with and without interleaved diffusion weighting. The results also indicated a predominant extravascular contribution to the BOLD signal time courses, including post-stimulation undershoots in both SE and GE measurements at 7 T.
本研究旨在利用动态扩散加权磁共振波谱技术，在7T场强下区分血管内和血管外因素对自旋回波（SE）和梯度回波（GE）血氧水平依赖（BOLD）信号的贡献。我们使用点分辨波谱序列同时采集了扩散权重为0、600和1200 s/mm²的SE和GE数据。通过将从SE中心开始的自由感应衰减拟合为单指数衰减函数来量化BOLD信号。在没有扩散加权的情况下，刺激期间SE和GE测量的BOLD信号分别增加了1.6±0.5%（TE = 40 ms）和5.2±1.4%（标称TE = 40 ms）。在有扩散加权的情况下，刺激期间SE测量的BOLD信号增加量从1.6±0.5%降至1.3±0.4%（P < 0.001），而GE测量的增加量未受影响（P > 0.05）；在SE和GE测量中，刺激后BOLD信号时间曲线中的负向波在很大程度上得以保留。这些结果证明了在有和没有交错扩散加权的情况下同时进行SE和GE测量BOLD信号的可行性。结果还表明，血管外因素对BOLD信号时间曲线起主要作用，包括在7T场强下SE和GE测量中的刺激后负向波。
