Aso Toshihiko, Urayama Shin-ichi, Poupon Cyril, Sawamoto Nobukatsu, Fukuyama Hidenao, Le Bihan Denis
Human Brain Research Center, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Neuroimage. 2009 Oct 1;47(4):1487-95. doi: 10.1016/j.neuroimage.2009.05.027. Epub 2009 May 18.
To disentangle the temporal profiles of the diffusion and BOLD components of diffusion-weighted functional MRI (DfMRI) during visual activation, we extracted the raw signal from an anatomically defined volume of interest encompassing the visual cortex of 16 subjects. Under the assumption of a linear, time invariant system we were able to define an intrinsic diffusion response function (DRF) from neural tissue, as a counterpart to the hemodynamic response function (HRF) commonly used in BOLD-fMRI. The shape of the DRF response was found to be very similar to the time courses of optical imaging transmittance signals, thought to originate from local geometric changes in brain tissue at the microscopic scale. The overall DfMRI signal response was modeled as the convolution of the stimulation paradigm time course with a DhRF, which is the sum of the DRF and a fractional HRF resulting from residual tissue T2-BOLD contrast. The contribution of the HRF to the DfMRI signal was found to be 26% at peak amplitude, but the DRF component which has a much steeper onset contributed solely at beginning of the response onset. The suitability of this model over the canonical HRF to process DfMRI data was then demonstrated on datasets acquired in 5 other subjects using a rapid event-related design. Some non-linearities in the responses were observed, mainly after the end of the stimulation.
为了厘清视觉激活期间扩散加权功能磁共振成像（DfMRI）中扩散和血氧水平依赖（BOLD）成分的时间特征，我们从16名受试者视觉皮层的解剖学定义感兴趣区域提取了原始信号。在线性、时不变系统的假设下，我们能够从神经组织中定义一个内在扩散响应函数（DRF），作为BOLD功能磁共振成像中常用的血流动力学响应函数（HRF）的对应物。发现DRF响应的形状与光学成像透射率信号的时间进程非常相似，据认为这源于微观尺度上脑组织的局部几何变化。整体DfMRI信号响应被建模为刺激范式时间进程与DhRF的卷积，DhRF是DRF与由残余组织T2-BOLD对比度产生的分数HRF之和。发现HRF对DfMRI信号的贡献在峰值幅度时为26%，但具有更陡峭起始的DRF成分仅在响应起始时起作用。然后，在使用快速事件相关设计对其他5名受试者采集的数据集上，证明了该模型相对于标准HRF处理DfMRI数据的适用性。在响应中观察到一些非线性，主要在刺激结束后。
