Laminar Perfusion Imaging

项目摘要 本项目的目标是进一步开发和优化下一代动脉自旋标记（ASL） 在皮质层和柱水平上定量绘制微血管灌注的技术， 第一个FDA批准的超高频（UHF）系统，7 T Terra。血氧水平依赖性（BOLD） 功能磁共振成像（fMRI）是研究宏观脑动力学的最广泛的非侵入性成像方式 网络和介观脑回路。然而，BOLD造影剂易受软脑膜静脉污染的影响 会严重干扰层状功能磁共振成像脑血流量（CBF）或微血管 通过ASL测量的灌注是用于体内评估神经血管功能的关键参数。的ASL 信号定位于接近神经激活的部位，并提供定量CBF的独特能力 在静止和任务激活期间的测量。我们开创了层流灌注成像，使用3D内- 容积GRASE（梯度和自旋回波）ASL，7 T，空间分辨率约为1 mm 3。然而，一个子- 毫米空间分辨率，并且理想地在~0.1mm3（或~0.5x0.5x0.5mm3）的水平，需要可靠的 神经活动在皮层层和列的分化，以及与状态的比较， 最先进的BOLD和CBV功能磁共振成像我们将利用我们实验室的一些最新技术突破： 用于7 T层流灌注成像的具有优化自旋标记策略的前沿ASL脉冲序列; 2)一种新的k-tCAIPIRANHA格式和TGV正则化 鲁棒欠采样模式和约束重构算法; 3）一种新的去噪算法 我们小组发明的称为k空间加权图像平均（KWIA）的技术， 热噪声降低50%，动态MRI的信噪比（SNR）提高一倍， 空间和时间分辨率。然后，我们将应用先进的ASL方法来精确测量 静息状态下脑组织跨皮层的灌注、动脉通过时间（ATT）和T1，以及 为了精确测量跨皮层层和列的任务引起的灌注信号变化， 感觉运动刺激和工作记忆任务。作为一个探索性的目标，我们将进一步开发一个 用于在7 T下同时测量T2 w BOLD、CBF和CBV对比度的创新脉冲序列 代谢活动的介观成像。已开发的ASL技术和研究成果将 对基础和临床神经科学研究都有很高的价值。我们还将评估开发的下一个- 在3 T下生成ASL脉冲序列和后处理算法，并将这些技术推广到 其他拥有3和/或7 T MR系统的研究中心，以促进我们的技术被 神经科学界

PROJECT SUMMARY The goal of this project is to further develop and optimize the next generation arterial spin labeling (ASL) technologies for quantitative mapping of microvascular perfusion at the level of cortical layers and columns on the first FDA approved ultrahigh magnetic (UHF) system, the 7T Terra. Blood oxygen level dependent (BOLD) fMRI is the most widely used non-invasive imaging modality for studying the dynamics of macroscopic brain networks and mesoscopic brain circuits. However, BOLD contrast is susceptible to contaminations of pial veins on the cortical surface that significantly confounds laminar fMRI. Cerebral blood flow (CBF) or microvascular perfusion measured by ASL is a key parameter for in vivo assessment of neurovascular function. The ASL signal is localized close to the site of neural activation and offers the unique capability for quantitative CBF measurements both at rest and during task activation. We pioneered laminar perfusion imaging using 3D inner- volume GRASE (Gradient and Spin Echo) ASL at 7T with a spatial resolution of ~1mm3. However, a sub- millimeter spatial resolution, and ideally at the level of ~0.1mm3 (or ~0.5x0.5x0.5mm3), is required for reliable differentiation of neural activities across cortical layers and columns, as well as for comparison with the state- of-the-art BOLD and CBV fMRI. We will take advantage of a few latest technical breakthroughs in our lab: 1) Cutting-edge ASL pulse sequences with optimized spin labeling strategies for laminar perfusion imaging at 7T; 2) A novel k-t CAIPIRANHA scheme in conjunction with a total-generalized-variation (TGV) regularized algorithm for robust under-sampling patterns and constrained reconstruction; and 3) A novel denoising technique termed k-space weighted image average (KWIA) invented by our group that is able to reduce the thermal noise by 50% and double the signal-to-noise ratio (SNR) of dynamic MRI without significantly affecting the spatial and temporal resolution. We will then apply the advanced ASL methods to precisely measure perfusion, arterial transit time (ATT) and T1 of brain tissue across cortical layers during resting state, as well as to precisely measure task induced perfusion signal changes across cortical layers and columns using sensorimotor stimulation and working memory tasks. As an exploratory aim, we will further develop an innovative pulse sequence for concurrent measurements of T2w BOLD, CBF and CBV contrasts at 7T for mesoscopic imaging of metabolic activities. The developed ASL technologies and research findings will be highly valuable to both basic and clinical neuroscientific research. We will also evaluate the developed next- generation ASL pulse sequences and post-processing algorithms at 3T, and disseminate these technologies to other sites with 3 and/or 7T MR systems to facilitate the widespread adoption of our technologies by the neuroscientific community.