Fast MRI at the Limit of Biological Temporal Resolution

 描述(申请人提供)：本项目的目标是测试联合假设，即更快地对功能磁共振(FMRI)信号进行更快数量级的采样可以帮助提取与神经元信号相关的信息；构成功能磁共振基础的血流动力学信号，而不是通常认为的迟缓，对神经元活动做出快速而准确的反应。通常提倡快速采样以实现生理性噪声去除--因为这些系统噪声源可以被充分采样，因此在原始fMRI信号中不会混叠--然而，我们的目标是证明短时间尺度的fMRI信号也包含由神经元激活直接驱动的波动。虽然众所周知，血氧水平依赖性(BOLD)反应在神经元活动开始后达到峰值6 S，但最初的血管反应开始于不到1 S。在这里，我们挑战这种BOLD反应是“慢”的观点。我们将利用我们最近开发的用于fMRI的同步多层(SMS)成像技术，它提供的时间采样速度比传统技术快12倍。使用短信方法，fMRI测量具有时间分辨率，可以检测整个大脑的激活，精确度为亚秒。以前的工作已经证明，以高采样率获取的fMRI时间序列数据可以用于将全球脑网络划分为更小的节点，从而在静息状态功能连通性研究中增加检测能力。在这里，我们建议将这一关键优势扩展到其他常见的功能磁共振实验范式。我们的初步数据表明，通过使用传统的任务驱动的块设计范例在更精细的时间尺度上获取fMRI数据，可以实现检测灵敏度的显著提高，最高可达2-3倍。在这些情况下，更快的采样产生更高的灵敏度。这一改进将使新的实验类别成为可能，以及单一受试者分析和潜在的个性化诊断。最近的侵袭性动物神经血管偶联研究和人类fMRI研究表明，BOLD反应的早期阶段精确地受局部血管反应的控制，并且BOLD反应随着时间在空间上传播。因此，高时空分辨率的功能磁共振成像采集可以通过对大胆反应的早期阶段进行采样来实现更高的准确性。在这些情况下，更快的采样产生更高的特异性。最后，我们将测试快速功能磁共振成像是否可以帮助(I)从连续的、时间编码的刺激设计中提取信息，以及(Ii)解决发生在时间上的神经元激活。对于后者，我们将实施一种新的校准程序，旨在从BOLD反应中测量的延迟中消除血管延迟的区域差异，以准确估计神经元激活的开始。在这里，更快的采样产生关于神经元功能和大脑激活潜伏期的额外信息。我们的目标是展示快速功能磁共振成像在这些领域的好处，并为不可避免地广泛使用这一变革性的新功能磁共振成像方法开发获取和分析框架。

 DESCRIPTION (provided by applicant): The objective of this project is to test the joint hypotheses that sampling the functional MRI (fMRI) signals up to an order of magnitude more rapidly can help extract information related to neuronal signaling; and that the hemodynamic signals that form the basis of fMRI, rather than being sluggish as is commonly believed, respond rapidly and precisely to neuronal activity. Rapid sampling is commonly advocated to enable physiological noise removal-because these systemic noise sources can then be adequately sampled and so are not aliased in the raw fMRI signal-however our goal is to demonstrate that the fMRI signal at short time scales also contains fluctuations that are directly driven by neuronal activation. While the blood-oxygen-level-dependent (BOLD) response is well known to peak 6 s following the onset of neuronal activity, the initial vascular response begins in less tha 1 s. Here we challenge the notion that the BOLD response is "slow". We will capitalize on our recent development of Simultaneous Multi-Slice (SMS) imaging for fMRI, which provides temporal sampling that is 12× faster than that of conventional techniques. With the SMS method, the fMRI measurement possesses the temporal resolution to detect brain activation over the entire brain with sub-second precision. Previous work has demonstrated that fMRI time series data acquired with high sampling rates can be used to parcellate global brain networks into smaller nodes, and therefore increase detection power in resting- state functional connectivity studies. Here we propose to extend this key benefit to other common fMRI experimental paradigms. Our preliminary data suggests that, by acquiring fMRI data on a finer time scale using a conventional task-driven block-design paradigm, dramatic increases in detection sensitivity up to factors of 2-3 are achievable. In these cases, faster sampling yields increased sensitivity. This boost will enable new classes of experiments, as well as single-subject analyses and potentially individualized diagnosis. Recent invasive animal neurovascular coupling studies and human fMRI studies have shown that the early stages of the BOLD response are precisely controlled by local vascular responses, and the BOLD response spreads spatially with time. High spatio-temporal resolution fMRI acquisitions can therefore enable higher accuracy by sampling the early phases of the BOLD response. In these cases, faster sampling yields increased specificity. Finally, we will test whether rapid fMRI can help (i) extrac information from continuous, temporally- encoded stimulus designs and (ii) resolve neuronal activations occurring closely in time. For the latter, we will implement a novel calibration procedure designed to remove regional variations in vascular delay from the measured delays in the BOLD response to accurately estimate the neuronal activation onset. Here, faster sampling yields additional information about neuronal function and activation latencies of the brain. Our aim is to demonstrate the benefits of rapid fMRI in these domains and to develop acquisition and analysis frameworks for the inevitable widespread use of this transformative new approach to fMRI.