Laminar Perfusion Imaging

项目总结 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)。 皮质层和柱状层水平的微血管灌注定量标测技术 FDA批准的第一个超高磁(UHF)系统，7T Terra。血氧水平依赖(粗体) 功能磁共振成像是目前应用最广泛的研究宏观脑动力学的无创性成像手段。 网络和中观大脑回路。然而，大胆的对比容易受到软脑膜静脉的污染。 在皮质表面，这明显混淆了层状功能磁共振成像。脑血流量(CBF)或微血管 ASL测量的血流灌注是在体评估神经血管功能的关键参数。ASL 信号位于神经激活部位附近，为定量脑血流提供了独特的能力 在静止状态和任务激活期间进行测量。我们开创了层流灌注成像的先河，使用了3D内- 体积梯度(梯度和自旋回声)ASL在7T，空间分辨率~1 mm~3。然而，一个子- 需要毫米级的空间分辨率，理想情况下达到~0.1mm3(或~0.5x0.5x0.5mm3)的水平 皮质层和皮质柱之间的神经活动的差异，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几项最新技术突破：1) 用于7T层流灌注成像的具有优化自旋标记策略的尖端ASL脉冲序列； 2)结合完全广义变分(TGV)正则化的k-t Caipiranha格式 稳健欠采样模式和约束重构算法；3)一种新的去噪方法 我们的团队发明了一种称为k空间加权图像平均(KWIA)的技术，它能够减少 热噪声降低50%，是动态MRI的信噪比(SNR)的两倍，而不会对 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质的灌注量、动脉通过时间(ATT)和T1，以及 要精确测量任务引起的跨皮质层和柱的灌注信号变化，请使用 感觉运动刺激和工作记忆任务。作为一个探索性目标，我们将进一步开发一种 创新的脉冲序列，用于同时测量T2W BOLD、CBF和CBV在7T时的对比度 代谢活动的介观成像。开发的ASL技术和研究成果将是 对基础和临床神经科学研究都有很高的价值。我们还将评估已开发的NEXT- 在3T上产生ASL脉冲序列和后处理算法，并将这些技术推广到 配备3和/或7T磁共振系统的其他站点，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.