Ultra-fast cerebral blood flow imaging for quantifying brain dynamics

摘要/项目摘要 血氧水平依赖（BOLD）功能磁共振成像广泛应用于神经科学研究。技术 近年来的进展使得能够在亚秒时间获得BOLD信号 分辨率，打开一个新的窗口，用于检查人脑的功能动态，例如休息- 功能磁共振成像。BOLD信号来源于脑血流量（CBF）和 代谢的变化，是复杂的;它作为神经活动的间接措施。直接 CBF变化的观察可以提供与神经活动更紧密耦合的信息。 动脉自旋标记（ASL）功能磁共振成像测量CBF的变化无创和定量，因此， 可以提供仅用BOLD不容易测量的有价值的动态信息。目前 现有的ASLFMRI方法受到低时间分辨率和信噪比（SNR）的限制， 主要是由于标记的血液到达脑组织所需的采集延迟。速度- 选择性（VS）ASL显示出减少延迟的承诺，但现有的标记策略不是 对于以高时间分辨率成像CBF是最佳的，例如低于2s，或者不具有足够的时间分辨率。 覆盖大脑。在这个概念验证开发项目中，我们提出了一个全新的VS 标记策略，以克服现有标记方法的问题，针对功能性CBF 测量具有大幅提高的时间分辨率（~ 1.5 s），SNR效率和良好的 覆盖在这个项目中开发的超快速和定量CBF成像方法应该有助于 推进我们对健康和疾病条件下大脑动力学的理解， 用于个体比较和/或纵向研究的首选成像工具。

Abstract/Project Summary Blood oxygenation level dependent (BOLD) fMRI is widely used in neuroscience studies. Technical advancement in the recently years has enabled BOLD signals to be acquired at sub-second temporal resolution, opening a new window for examining functional dynamics of the human brain, e.g. resting- state fMRI. The BOLD signal originates from the mismatch between cerebral blood flow (CBF) and metabolism changes, and is complex; it serves as an indirect measure of neural activities. A direct observation of CBF changes can provide information that is more closely coupled to neural activities. Arterial spin labeling (ASL) fMRI measures CBF changes noninvasively and quantitatively, therefore may provide valuable dynamic information that is not readily measured with BOLD alone. Currently the existing ASL fMRI methods are limited by low temporal resolution and signal-to-noise ratio (SNR), mainly due to acquisition delays required for the labeled blood to reach the brain tissue. Velocity- selective (VS) ASL shows promises in reducing the delays, but the existing labeling strategies are not optimal for imaging CBF at high temporal resolution, such as below 2 s, or do not have sufficient coverage of the brain. In this proof-of-concept development project, we propose a completely new VS labeling strategy to overcome the problems of existing labeling methods, aiming for functional CBF measurements with substantially increased temporal resolution (~ 1.5 s), SNR efficiency and a good coverage. The ultra-fast and quantitative CBF imaging method developed in this project should help advance our understanding of brain dynamics under healthy and diseased conditions, and may be an imaging tool of choice for individual comparison and/or longitudinal studies.