Objective

This review article gives an account of the development of the MR-encephalography (MREG) method, which started as a mere ‘Gedankenexperiment’ in 2005 and gradually developed into a method for ultrafast measurement of physiological activities in the brain. After going through different approaches covering k-space with radial, rosette, and concentric shell trajectories we have settled on a stack-of-spiral trajectory, which allows full brain coverage with (nominal) 3 mm isotropic resolution in 100 ms. The very high acceleration factor is facilitated by the near-isotropic k-space coverage, which allows high acceleration in all three spatial dimensions.

Methods

The methodological section covers the basic sequence design as well as recent advances in image reconstruction including the targeted reconstruction, which allows real-time feedback applications, and—most recently—the time-domain principal component reconstruction (tPCR), which applies a principal component analysis of the acquired time domain data as a sparsifying transformation to improve reconstruction speed as well as quality.

Applications

Although the BOLD-response is rather slow, the high speed acquisition of MREG allows separation of BOLD-effects from cardiac and breathing related pulsatility. The increased sensitivity enables direct detection of the dynamic variability of resting state networks as well as localization of single interictal events in epilepsy patients. A separate and highly intriguing application is aimed at the investigation of the glymphatic system by assessment of the spatiotemporal patterns of cardiac and breathing related pulsatility.

Discussion

MREG has been developed to push the speed limits of fMRI. Compared to multiband-EPI this allows considerably faster acquisition at the cost of reduced image quality and spatial resolution.

中文翻译：

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15 年 MR 脑造影

客观的

这篇综述文章介绍了 MR 脑成像 (MREG) 方法的发展，该方法于 2005 年开始只是一个“Gedankenexperiment”，并逐渐发展成为一种超快速测量大脑生理活动的方法。在经历了用径向、玫瑰花结和同心壳轨迹覆盖 k 空间的不同方法之后，我们确定了螺旋轨迹堆栈，它允许在 100 毫秒内以（标称）3 毫米各向同性分辨率覆盖整个大脑。接近各向同性的 k 空间覆盖促进了非常高的加速因子，这允许在所有三个空间维度上实现高加速。

方法

方法部分涵盖了基本序列设计以及图像重建的最新进展，包括允许实时反馈应用的目标重建，以及最近的时域主成分重建 (tPCR)，它应用了主成分将获取的时域数据作为稀疏变换进行分析，以提高重建速度和质量。

应用

尽管 BOLD 响应相当缓慢，但 MREG 的高速采集允许将 BOLD 效应与心脏和呼吸相关的搏动分开。增加的灵敏度能够直接检测静息状态网络的动态变化以及癫痫患者单个发作间期事件的定位。一个单独且非常有趣的应用程序旨在通过评估心脏和呼吸相关搏动的时空模式来研究类淋巴系统。

讨论

MREG 已被开发用于推动 fMRI 的速度限制。与多波段 EPI 相比，这允许以降低的图像质量和空间分辨率为代价的更快的采集。