Fast MRI at the Limit of Biological Temporal Resolution

 描述（由申请人提供）：本项目的目的是测试联合假设，即更快地对功能性MRI（fMRI）信号进行一个数量级的采样可以帮助提取与神经元信号相关的信息;并且形成fMRI基础的血液动力学信号，而不是像通常认为的那样缓慢，对神经元活动做出快速准确的反应。快速采样通常被提倡，以使生理噪声去除，因为这些系统的噪声源，然后可以充分采样，所以没有混叠的原始fMRI信号，然而，我们的目标是证明，在短时间尺度的fMRI信号也包含波动，直接驱动的神经元激活。众所周知，血氧水平依赖性（BOLD）反应在神经元活动开始后6秒达到峰值，而初始血管反应在不到1秒内开始。在这里，我们挑战的概念，大胆的反应是“慢”。我们将利用我们最近开发的功能磁共振成像同步多切片（SMS）成像，它提供的时间采样比传统技术快12倍。使用SMS方法，fMRI测量具有时间分辨率，可以以亚秒级精度检测整个大脑的大脑激活。 先前的工作已经证明，以高采样率获得的功能磁共振成像时间序列数据可以用于将全球脑网络包裹成更小的节点，从而增加静息状态功能连接研究中的检测能力。在这里，我们建议扩展到其他常见的功能磁共振成像实验范例的关键好处。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式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2-3倍的显着增加。在这些情况下，更快的采样产生更高的灵敏度。这一推动将使新的实验类别，以及单一主题的分析和潜在的个性化诊断成为可能。最近的侵入性动物神经血管耦合研究和人类fMRI研究表明，BOLD反应的早期阶段是由局部血管反应精确控制的，并且BOLD反应随时间在空间上扩散。因此，高时空分辨率的fMRI采集可以通过对BOLD响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和（ii）解决神经元激活发生的时间密切相关。对于后者，我们将实施一种新的校准程序，旨在从BOLD响应的测量延迟中去除血管延迟的区域变化，以准确估计神经元激活开始。在这里，更快的采样产生关于神经元功能和大脑激活的额外信息。我们的目标是证明快速功能磁共振成像在这些领域的好处，并制定收购和分析框架的不可避免的广泛使用这种变革性的新方法功能磁共振成像。

 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.