SPATIO-TEMPORAL POINT-SPREAD FUNC OF FMRI SIGNAL IN HUMAN GRAY MATTER AT 7 TESLA

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者的研究机构。 本研究探讨了灰质中血氧水平依赖（BOLD）功能性MRI（fMRI）信号的时空特性，排除了大血管的混杂、不准确的贡献。我们量化了BOLD反应的空间特异性，并研究了这种特异性是否随刺激开始的时间而变化。在7特斯拉（T）下进行fMRI，其中容易检测到实质起源的映射信号。两个相邻的视觉刺激进行了调整，以引起集中在一个平坦的灰质区域在V1的反应。fMRI信号以高分辨率正交于刺激表示之间的视网膜定位边界进行采样。来自大血管的信号被掩盖。主成分分析显示，空间中的第一个成分占随时间变化的96.2+/-1.6%。该时不变响应的空间分布与由阶跃函数和高斯点扩散函数（PSF）的卷积组成的模型拟合。拟合PSF的平均半高全宽为2.34+/-0.20 mm。基于混杂效应的模拟，我们估计，BOLD PSF在人类灰质是小于2毫米。一个时间点到时间点的分析表明，PSF获得的第三个刺激第5秒（1.52 mm）和第4秒（1.99 mm）的平均PSF比刺激第5秒（2.42+/-0.15 mm）获得的平均PSF窄。响应区域的边缘位置从刺激区域的边界偏移（1.72+/-0.07 mm），指示空间非线性。模拟显示，当使用宽度等于成像的柱状组织的周期的PSF成像时，活性柱和非活性柱之间的有效对比度降低25倍。因此，在人类灰质中的高氧BOLD响应的PSF比在1.5 T下报告的窄，其中大血管占主导地位的映射信号。这种响应的初始阶段比以后的阶段更具有空间特异性。抑制大血管信号的数据采集方法应增加BOLD fMRI的空间特异性。最佳刺激持续时间的选择代表了空间特异性和与短刺激持续时间相关的开销之间的权衡。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study investigated the spatio-temporal properties of blood-oxygenation level-dependent (BOLD) functional MRI (fMRI) signals in gray matter, excluding the confounding, inaccurate contributions of large blood vessels. We quantified the spatial specificity of the BOLD response, and we investigated whether this specificity varies as a function of time from stimulus onset. fMRI was performed at 7 Tesla (T), where mapping signals of parenchymal origin are easily detected. Two abutting visual stimuli were adjusted to elicit responses centered on a flat gray matter region in V1. fMRI signals were sampled at high-resolution orthogonal to the retinotopic boundary between the representations of the stimuli. Signals from macro-vessels were masked out. Principal component analysis revealed that the first component in space accounted for 96.2+/-1.6% of the variance over time. The spatial profile of this time-invariant response was fitted with a model consisting of the convolution of a step function and a Gaussian point-spread-function (PSF). The mean full-width at half-maximal-height of the fitted PSF was 2.34+/-0.20 mm. Based on simulations of confounding effects, we estimate that BOLD PSF in human gray matter is smaller than 2 mm. A time-point to time-point analysis revealed that the PSF obtained during the 3rd (1.52 mm) and 4th (1.99 mm) seconds of stimulation were narrower than the mean PSF obtained from the 5th second on (2.42+/-0.15 mm). The position of the edge of the responding region was offset (1.72+/-0.07 mm) from the boundary of the stimulated region, indicating a spatial non-linearity. Simulations showed that the effective contrast between active and non-active columns is reduced 25-fold when imaged using a PSF whose width is equal to the cycle of the imaged columnar organization. Thus, the PSF of the hyper-oxygenated BOLD response in human gray matter is narrower than that reported at 1.5 T, where macro-vessels dominate the mapping signals. The initial phase of this response is more spatially specific than later phases. Data acquisition methods that suppress macro-vascular signals should increase the spatial specificity of BOLD fMRI. The choice of optimal stimulus duration represents a trade-off between the spatial specificity and the overhead associated with short stimulus duration.