Advanced MRI section, Laboratory of Functional and Molecular Imaging, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
Advanced MRI section, Laboratory of Functional and Molecular Imaging, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
Magn Reson Imaging. 2021 Dec;84:135-144. doi: 10.1016/j.mri.2021.09.014. Epub 2021 Oct 6.
The study of the brain's functional organization at laminar and columnar level of the cortex with blood oxygenation-level dependent (BOLD) functional MRI (fMRI) is affected by the contribution of large veins downstream from the microvascular response to brain activity. Blood volume- and especially perfusion-based techniques may reduce this problem because of their reduced sensitivity to venous effects, but may not allow the same spatial resolution because of smaller signal changes associated with brain activity. Here we investigated the practical resolution limits of perfusion-weighted fMRI in human visual stimulation experiments. For this purpose, we used a highly sensitive, single-shot perfusion labeling (SSPL) technique at 7 T and compared sensitivity to detect visual activation at low (2 mm, n = 10) and high (1 mm, n = 8) nominal isotropic spatial, and 3 s temporal, resolution with BOLD in 5½-minute-long experiments. Despite the smaller absolute signal change with activation, 2 mm resolution SSPL yielded comparable sensitivity to BOLD. This was attributed to a superior suppression of physiological noise with SSPL. However, at 1 mm nominal resolution, SSPL sensitivity fell on average at least 42% below that of BOLD, and detection of visual activation was compromised. This is explained by the fact that at high resolution, with both techniques, typically thermal noise rather than physiological noise dominates sensitivity. The observed sensitivity loss implies that to perform 1-mm resolution, perfusion weighted fMRI with a robustness similar to BOLD, scan times that are almost 3 times longer than the comparable BOLD experiment are required. This is in line with or slightly better than previous comparisons between perfusion-weighted fMRI and BOLD. The lower sensitivity has to be weighed against the spatial fidelity advantages of high-resolution perfusion-weighted fMRI.
利用血氧水平依赖（BOLD）功能磁共振成像（fMRI）研究皮层的层状和柱状水平的大脑功能组织，会受到大脑活动微血流反应下游的大静脉贡献的影响。由于其对静脉效应的敏感性降低，基于血容量和灌注的技术可能会减少这个问题，但由于与大脑活动相关的信号变化较小，可能无法实现相同的空间分辨率。在这里，我们在人类视觉刺激实验中研究了灌注加权 fMRI 的实际分辨率限制。为此，我们在 7T 下使用了一种高灵敏度的单次激发灌注标记（SSPL）技术，并比较了在低（2mm，n=10）和高（1mm，n=8）空间分辨率和 3s 时间分辨率下，SSPL 和 BOLD 检测视觉激活的灵敏度，实验时间为 5 分半钟。尽管激活时的绝对信号变化较小，但 2mm 分辨率 SSPL 的灵敏度与 BOLD 相当。这归因于 SSPL 对生理噪声的更好抑制。然而，在 1mm 名义分辨率下，SSPL 的灵敏度平均下降至少 42%，低于 BOLD，从而影响了视觉激活的检测。这是因为在高分辨率下，两种技术通常是热噪声而不是生理噪声主导灵敏度。观察到的灵敏度损失意味着，要以与 BOLD 相似的稳健性进行 1mm 分辨率的灌注加权 fMRI，需要的扫描时间几乎是可比 BOLD 实验的 3 倍。这与灌注加权 fMRI 和 BOLD 之间的先前比较一致或稍好。必须权衡低灵敏度与高分辨率灌注加权 fMRI 的空间保真度优势。
