Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany.
Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany.
MAGMA. 2021 Feb;34(1):85-108. doi: 10.1007/s10334-020-00891-z. Epub 2020 Oct 20.
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.
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.
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.
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.
本文回顾了磁共振脑功能成像（MREG）方法的发展历程。该方法始于 2005 年的一个“思想实验”，逐渐发展成为一种用于测量大脑生理活动的超快方法。在经历了涵盖径向、梅花形和同心壳轨迹的 k 空间的不同方法之后，我们选择了螺旋堆栈轨迹，该轨迹允许在 100ms 内以（名义上）3mm 的各向同性分辨率覆盖整个大脑。非常高的加速因子得益于近各向同性的 k 空间覆盖，这允许在所有三个空间维度上进行高加速。
方法部分涵盖了基本序列设计以及图像重建的最新进展，包括实时反馈应用的靶向重建，以及最近的时域主成分重建（tPCR），它对采集的时域数据进行主成分分析作为稀疏变换，以提高重建速度和质量。
尽管 BOLD 反应相当缓慢，但 MREG 的高速采集允许从心脏和呼吸相关脉动中分离出 BOLD 效应。灵敏度的提高使得能够直接检测静息状态网络的动态变化，并定位癫痫患者的单个癫痫发作事件。一个单独的、非常有趣的应用是通过评估心脏和呼吸相关脉动的时空模式来研究糖质系统。
MREG 的发展旨在推动 fMRI 的速度极限。与多频带 EPI 相比，这允许以牺牲图像质量和空间分辨率为代价进行更快的采集。
