Next-Generation fMRI with MB-SWIFT: Insights into the Origins of Contrast

摘要 我们的长期目标是建立新开发的名为多波段的零回波时间磁共振脉冲序列 傅里叶变换扫描成像(MB-SWIFT)作为人工制品的下一代选择方法- 人体内自由、安静、高分辨率的功能磁共振成像，适用于通过与细胞机制相连的细胞机制检测神经元活动 到使用标准读出序列本质上无法达到的电事件。MB-SWIFT已被 已经证明，与目前的fMRI技术相比，它具有显著的优势，因为它是最低限度的 受易感性伪影的影响，对运动有很高的耐受性，并产生几乎无声的、连续的 由于使用了缓慢切换的梯度，采集过程中的声学噪声。然而，这一现象的起源 到目前为止，功能对比仍然难以捉摸。我们的一般假设是MB-SWIFT功能信号 密切反映了局部场势的变化。我们还提出了这样的假设，即不可忽略的部分 这种对比可能产生于T1对比机制，该对比机制涉及最有可能的固定自旋池 对神经元电流敏感。在进行一项全面的研究来阐明放松机制是如何 与膜电位和离子再分布影响MB-SWIFT信号有关，我们首先需要验证 MB-SWIFT信号是神经元活动的敏感指标，并决定它们是否实质上 由松弛机制调节，而不是由血流或氧合变化来解释。因此，目前的证据是- 啮齿动物的概念研究将首先确定MB-SWIFT信号在多大程度上反映神经元的变化 通过MB-SWIFT和电生理采集fMRI信号的清醒、生理条件下的活动 在不同持续时间和频率的胡须刺激下，在躯体感觉皮层进行记录。那么，我们会 评估MB-SWIFT信号对氧合水平和脑血液变化的敏感程度 通过在气体挑战期间进行机理研究来流动，使用不同的线圈设计旨在隔离 流入贡献，并与不同的磁场，意在验证T1的存在-可能的机制 组织起源。通过实现这些目标，我们将深入了解MB-SWIFT功能磁共振成像的基本原理 信号，并将达到最初的里程碑，将推动MB-SWIFT在检测神经元电流方面取得进展 这个目标已经被守护了20多年。此外，机械论研究的意义 将扩展到MB-SWIFT之外，并且它们将与几乎零回波时间的其他MRI方法相关。

ABSTRACT Our long term goal is to establish the newly developed zero echo time MRI pulse sequence entitled Multi-Band SWeep Imaging with Fourier Transformation (MB-SWIFT) as the next-generation method of choice for artefact- free, quiet, high-resolution fMRI in humans, suitable for detecting neuronal activity via cellular mechanisms linked to electrical events that are intrinsically unattainable with standard readout sequences. MB-SWIFT has been already proven to offer remarkable advantages as compared to current fMRI techniques, since it is minimally impacted by susceptibility artefacts, has high tolerance for movement, and produces a nearly silent, continuous acoustic noise during acquisitions thanks to the use of slowly switching gradients. However, the origin of the functional contrast has remained elusive so far. Our general hypothesis is that MB-SWIFT functional signals closely reflect changes in local field potentials. We also advance the hypothesis that a non-negligible portion of the contrast may arise from T1 contrast mechanisms involving the pool of immobilized spins that are most likely sensitized to neuronal currents. Before undertaking a full-blown study that elucidates how relaxation mechanisms linked to membrane potentials and ions redistributions impact MB-SWIFT signals, we first need to validate that MB-SWIFT signals are sensitive proxies of neuronal activity, and determine whether they are substantially mediated by relaxation mechanisms not explained by blood flow or oxygenation changes. Ergo, the current proof- of-concept study in rodents will first establish to what extent MB-SWIFT signals reflect changes in neuronal activity under awake, physiological conditions by acquiring fMRI signals with MB-SWIFT and electrophysiological recording in somatosensory cortex during whisker stimulations of different duration and frequency. Then, we will evaluate to what extent MB-SWIFT signals are sensitive to changes in oxygenation levels and cerebral blood flow by conducting mechanistic studies during gas challenges, with different coil designs meant to isolate the inflow contribution, and with different magnetic fields, meant to verify the presence of T1-mechanisms of possible tissue origin. By achieving these aims we will gain pivotal insights into the substrates of the MB-SWIFT fMRI signals, and will reach initial milestones that will advance MB-SWIFT towards detection of neuronal currents, a goal that has been looked after for more than 20 years. In addition, the implications of the mechanistic studies will expand beyond MB-SWIFT, and they will be relevant to other MRI approaches with virtually zero echo time.