Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan; Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland.
Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan; School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
Neuroimage. 2011 Jul 1;57(1):140-148. doi: 10.1016/j.neuroimage.2011.04.006. Epub 2011 Apr 12.
Spin-echo diffusion-weighted functional MRI (DW-fMRI) was performed on a rat forepaw electrostimulation model at 7 T. This small animal model used electric (rather than visual) stimulation and allowed DW-fMRI experiments to be performed over a broader range of acquisition parameters than previous work on humans and cats. Resting state experiments with injections of ultra-small superparamagnetic iron oxide (USPIO) were also used to investigate the effects of gradient coupling on the signal change. The experiments were performed over five b-values (0, 200, 800, 1400 and 2000s/mm(2)) and three echo-times (30, 60 and 90 ms). Alterations to the stimulation-induced response with respect to TE and b-value were evaluated in two intervals: the positive stimulus-correlated response (5-20s after stimulus onset) and the post-stimulus undershoot (27-40s). There was no strong dependence of the signal change on b-value for any of the intervals or TEs. Similarly, changes to the apparent transverse relaxation rate showed no clear dependence on b-value. In contrast to previous DW-fMRI studies, the simplest explanation for the observed data is a single-compartment signal model with the functional signal changes probably corresponding to extravascular SE-BOLD. Experiments with USPIO suggested that at 7 T and within the range of parameters used, the influence of gradient coupling may be sufficient to explain minor DW-fMRI signal changes.
在 7T 大鼠前爪电刺激模型上进行了自旋回波扩散加权功能磁共振成像（DW-fMRI）。该小动物模型使用电刺激（而非视觉刺激），并允许在比以前在人类和猫身上进行的工作更广泛的采集参数范围内进行 DW-fMRI 实验。还使用超小超顺磁氧化铁（USPIO）注射进行静息状态实验，以研究梯度耦合对信号变化的影响。实验在五个 b 值（0、200、800、1400 和 2000s/mm²）和三个回波时间（30、60 和 90ms）下进行。在两个间隔内评估了 TE 和 b 值对刺激诱导响应的改变：正刺激相关响应（刺激开始后 5-20s）和刺激后下冲（27-40s）。对于任何间隔或 TE，信号变化都没有强烈依赖于 b 值。同样，表观横向弛豫率的变化也没有明显依赖于 b 值。与以前的 DW-fMRI 研究相反，观察到的数据的最简单解释是单室信号模型，功能信号变化可能对应于血管外 SE-BOLD。USPIO 实验表明，在 7T 且在使用的参数范围内，梯度耦合的影响可能足以解释较小的 DW-fMRI 信号变化。
