Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan.
Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan; Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan.
Neuroimage. 2014 Sep;98:258-65. doi: 10.1016/j.neuroimage.2014.04.050. Epub 2014 Apr 26.
Diffusion-weighted (DW) functional magnetic resonance imaging (fMRI) signal changes have been noted as a promising marker of neural activity. Although there is no agreement on the signal origin, the blood oxygen level dependent (BOLD) effect has figured as one of the most likely sources. In order to investigate possible BOLD and non-BOLD contributions to the signal, DW fMRI was performed on normal volunteers using a sequence with two echo-planar acquisitions after pulsed-gradient spin-echo. Along with the changes to the signal amplitude (ΔS/S) measured at both echo-times, this sequence allowed changes to the transverse relaxation rate (ΔR2) to be estimated for multiple b-values during hypercapnia (HC) and visual stimulation (VS). ΔS/S and ΔR2 observed during HC were relatively insensitive to increasing b-value. On the other hand, ΔS/S demonstrated a clear dependence on b-value at both echo-times for VS. In addition, ΔR2 during the latter half of VS was significantly more negative at b=1400s/mm(2) than for the time-courses at lower b-value, but ΔR2 during the post-stimulus undershoot was independent of b-value. The results have been discussed in terms of two models: the standard intravascular-extravascular model for fMRI and a three-compartment model (one intra- and two extravascular compartments). Within these interpretations the results suggest that the majority of the response is linked to changes in transverse relaxation, but possible contributions from other sources may not be ruled out.
弥散加权（DW）功能磁共振成像（fMRI）信号变化已被认为是神经活动的一个有前途的标志物。尽管对于信号的起源尚无共识，但血氧水平依赖（BOLD）效应已成为最有可能的来源之一。为了研究信号中可能存在的 BOLD 和非 BOLD 贡献，使用脉冲梯度自旋回波后进行两次回波平面采集的序列对正常志愿者进行了 DW fMRI 检查。除了在两个回波时间测量的信号幅度变化（ΔS/S）外，该序列还允许在高碳酸血症（HC）和视觉刺激（VS）期间为多个 b 值估计横向弛豫率变化（ΔR2）。在 HC 期间观察到的ΔS/S 和ΔR2 对 b 值的增加相对不敏感。另一方面，在 VS 期间，ΔS/S 在两个回波时间都显示出与 b 值的明显依赖性。此外，在 b=1400s/mm(2)时，VS 后半段的ΔR2 明显比低 b 值时的时间过程更负，但刺激后下冲期间的ΔR2 与 b 值无关。结果已根据两种模型进行了讨论： fMRI 的标准血管内外模型和三腔室模型（一个血管内和两个血管外腔室）。在这些解释中，结果表明，大多数反应与横向弛豫的变化有关，但不能排除其他来源的可能贡献。
