Spin-echo fMRI in humans using high spatial resolutions and high magnetic fields
Spin-echo fMRI in humans using high spatial resolutions and high magnetic fields
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DOI：
10.1002/mrm.10433
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发表时间：
2003-04-01
影响因子：
3.3
通讯作者：
Hu, XP
中科院分区：
文献类型：
--
作者：
Yacoub, E;Duong, TQ;Hu, XP
Hahn自旋回波（HSE）为基础的BOLD效应在高磁场预计提供功能图像，完全源于微血管。在低磁场下主导HSE BOLD对比度的血液贡献（例如，1.5 T），并降低特异性，在高磁场下被高度衰减，因为HSE实验中静脉血的表观T-2随着磁场的增加而二次降低。相反，HSE BOLD对比度被认为是由微血管系统产生的，并且随着磁场强度超线性地增加。在这项工作中，我们报告的HSE BOLD信号变化的详细和定量评估的结果，在人类视觉皮层的功能成像在4和7 T。本研究使用了高空间分辨率（由较高场强和表面线圈的信噪比（SNR）增加提供），以避免部分容积效应（PVE），并证明了较高场强下的对比度噪声比（CNR）和空间特异性增加。由视觉刺激引起的HSE BOLD信号变化主要是线性依赖于回波时间（TE）。当使用Stejskal-Tanner梯度抑制血液贡献时，由于血液的不均匀流动和相对于组织的更高扩散常数，它们的幅度在从4 T到7 T的过程中几乎以二次方的方式增加。在7 T的HSE信号的变化，准确地建模使用的血管体积为1.5%，与灰质的毛细血管体积。此外，高分辨率采集表明，由于白色物质或脑脊液空间相对于灰质PVE的减少，CNR随着体素尺寸< 1 mm而增加（3）。得出的结论是，高场HSE功能性MRI（fMRI）信号主要来源于毛细血管，并且与脑功能相关的信号变化的幅度在7 T时达到足够高的水平，使其成为在毫米到亚毫米空间尺度上进行映射的有用方法。(C)2003 Wiley-Liss，Inc.
The Hahn spin-echo (HSE)-based BOLD effect at high magnetic fields is expected to provide functional images that originate exclusively from the microvasculature. The blood contribution that dominates HSE BOLD contrast at low magnetic fields (e.g., 1.5 T), and degrades specificity, is highly attenuated at high fields because the apparent T-2 of venous blood in an HSE experiment decreases quadratically with increasing magnetic field. In contrast, the HSE BOLD contrast is believed to arise from the microvasculature and increase supralinearly with the magnetic field strength. In this work we report the results of detailed and quantitative evaluations of HSE BOLD signal changes for functional imaging in the human visual cortex at 4 and 7 T. This study used high spatial resolution, afforded by the increased signal-to-noise ratio (SNR) of higher field strengths and surface coils, to avoid partial volume effects (PVEs), and demonstrated increased contrast-to-noise ratio (CNR) and spatial specificity at the higher field strengths. The HSE BOLD signal changes induced by visual stimulation were predominantly linearly dependent on the echo time (TE). They increased in magnitude almost quadratically in going from 4 to 7 T when the blood contribution was suppressed using Stejskal-Tanner gradients that suppress signals from the blood due to its inhomogeneous flow and higher diffusion constant relative to tissue. The HSE signal changes at 7 T were modeled accurately using a vascular volume of 1.5%, in agreement with the capillary volume of gray matter. Furthermore, high-resolution acquisitions indicate that CNR increased with voxel sizes < 1 mm(3) due to diminishing white matter or cerebrospinal fluid-space vs. gray matter PVEs. It was concluded that the high-field HSE functional MRI (fMRI) signals originated largely from the capillaries, and that the magnitude of the signal changes associated with brain function reached sufficiently high levels at 7 T to make it a useful approach for mapping on the millimeter to submillimeter spatial scale. (C) 2003 Wiley-Liss, Inc.