fMRI Technologies for Imaging at the Limit of Biological Spatiotemporal Resolution: Administrative Supplement

用于生物时空分辨率极限成像的 fMRI 技术：行政补充

• 批准号: 10833383
• 负责人: Jonathan Rizzo Polimeni
• 金额: $ 4.55万
• 依托单位: MASSACHUSETTS GENERAL HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2024-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10833383
• 关键词: Administrative Supplement; Animal Model; Biological; Blood Vessels; Blood flow; Brain; Cerebrovascular system; Coupled; Deposition; Echo-Planar Imaging; Endowment; Exhibits; Functional Magnetic Resonance Imaging; Funding; Goals; Human; Image; Imaging technology; Knowledge; Location; Magnetic Resonance Imaging; Measures; Methods; Motion; Neurons; Neurosciences; Oxygen; Phase; Physiologic pulse; Resolution; Sampling; Signal Transduction; Specificity; Technology; Testing; Time; blood oxygenation level dependent response; design; experimental study; imaging study; improved; novel; optical imaging; response; spatiotemporal; theories; tool; transmission process

PROJECT SUMMARY / ABSTRACT Functional MRI (fMRI) is the most widely-used tool to noninvasively measure brain function and has produced much of our current knowledge about the functional organization of the human brain. All fMRI methods, however, measure neuronal activity indirectly by tracking the associated local changes in blood flow and oxygenation. While this is often viewed as a limitation of fMRI, recent optical imaging studies in animal models have shown that, surprisingly, the smallest blood vessels in the brain respond rapidly to local neuronal activity, and are thus tightly coupled to neurons, suggesting that fMRI could provide a far more veridical picture of neuronal activity than previously believed—if one can measure fMRI signals such as BOLD exclusively from the microvasculature. In the previous funding cycle, we successfully tested our hypothesis that the neuronal specificity of fMRI can be improved by restricting analyses to the earliest phases of the standard gradient-echo BOLD response, thought to occur in the microvasculature, before the responses spread to larger blood vessels and become less spatially localized. The ability to reliably extract the earliest phases of the BOLD response was achieved through the fast temporal sampling made possible through the fMRI acquisition technologies we developed. Our findings were consistent with our hypothesis—the fastest component of the BOLD response provides the highest microvascular specificity. Here we test the converse hypothesis: that BOLD signals from the microvasculature are fastest and exhibit the highest temporal specificity, while signals from the macrovasculature are temporally delayed and smeared. To test this we will develop technologies for spin-echo BOLD, which exclusively measures from the microvasculature, with fast temporal sampling. In this cycle our central hypothesis is that spin-echo BOLD with exclusive sensitivity to the microvasculature, will yield higher temporal specificity than gradient-echo BOLD, which contains slower signals from the macrovasculature. The challenge is that spin-echo acquisitions in theory provide T2 weighting, endowing spin-echo BOLD with microvascular specificity, however in practice it is difficult to achieve pure T2 weighting. Thus, our goals are to develop and validate fMRI technologies for robust pure T2-weighted BOLD, and to test whether pure T2-weighted BOLD provides higher temporal specificity. These goals can only be achieved by combining several novel MRI technologies we have recently introduced. The core technology is Echo-Planar Time-Resolved Imaging (EPTI), an extension to Echo-Planar Imaging (EPI), which can provide pure T2-weighted BOLD—concurrently with T2*-weighted BOLD, enabling direct comparisons. We will combine this with our new methods for increasing temporal sampling efficiency through and motion-robustness, and maximizing signal when using fast sampling rates. Finally, all experiments will be performed at 7 Tesla, where BOLD exhibits stronger microvascular weighting and higher sensitivity compared to standard field strengths, using parallel transmit RF pulse designs to reduce power deposition and improve the spatial uniformity of fMRI sensitivity.

项目摘要 /摘要 功能性MRI（fMRI）是无创测量大脑功能的最广泛使用的工具，并已产生 我们当前关于人脑功能组织的知识。但是，所有fMRI方法 通过跟踪血流和氧合的相关局部变化，间接测量神经元活性。 虽然这通常被视为fMRI的限制，但动物模型中最近的光学成像研究已显示 令人惊讶的是，大脑中最小的血管对局部神经元活性迅速反应，因此 与神经元紧密耦合，表明fMRI可以提供更垂直的神经元活动图片 比以前认为的比以前认为的，如果可以测量仅来自微脉管系统的fMRI信号，例如仅大胆的信号。 在上一个资金周期中，我们成功地检验了我们的假设，即fMRI的神经元特异性可以 通过将分析限制为标准梯度回答的最早阶段，可以改善 在响应扩散到较大的血管之前，发生在微脉管系统中并变得越来越频繁 本地化。通过快速实现了可靠提取粗体响应的最早阶段的能力 通过我们开发的功能磁共振成像采集技术使临时抽样成为可能。我们的发现是 与我们的假设一致 - 大胆响应的最快组成部分提供了最高 微血管特异性。在这里，我们测试了相反的假设：来自微脉管系统的大胆信号 最快且暴露了最高的临时特异性，而来自大型的信号暂时是 延迟和涂抹。为了测试这一点，我们将开发用于Spin-Echo Bold的技术 来自微脉管系统，并具有快速的临时抽样。在这个周期中，我们的中心假设是自旋回波 大胆对微脉管系统具有独家敏感性，将产生比梯度回波更高的临时特异性 粗体，其中包含来自大型腔腔的信号较慢。挑战是自旋回波采集 理论上提供T2加权，以微血管特异性赋予Spin-Echo Bold，但实际上 很难实现纯T2加权。这是我们的目标是开发和验证功能磁共振成像技术的强大技术 纯T2加权大胆，并测试纯T2加权大胆是否提供了更高的临时特异性。 这些目标只能通过结合我们最近拥有的几种新型MRI技术来实现 引入。核心技术是回声 - 平面时间分辨成像（EPTI），一个Echo-Planar的扩展 成像（EPI），它可以提供纯T2加权大胆 - 与T2*加权大胆相处 直接比较。我们将将其与提高临时抽样效率的新方法结合起来 使用快速采样率时通过运动和运动型，并最大化信号。最后，所有实验 将在7特斯拉进行，大胆表现出更强的微血管加权和更高的灵敏度 与标准场强度相比，使用并行发射RF脉冲设计来减少功率沉积和 提高fMRI灵敏度的空间均匀性。