Garreffa G, Carnì M, Gualniera G, Ricci G B, Bozzao L, De Carli D, Morasso P, Pantano P, Colonnese C, Roma V, Maraviglia B
Department of Physics, University of Rome, La Sapienza, Rome, Italy.
Magn Reson Imaging. 2003 Dec;21(10):1175-89. doi: 10.1016/j.mri.2003.08.019.
The purpose of this study was the development of a real-time filtering procedure of MRI artifacts in order to monitor the EEG activity during continuous EEG/fMRI acquisition. The development of a combined EEG and fMRI technique has increased in the past few years. Preliminary "spike-triggered" applications have been possible because in this method, EEG knowledge was only necessary to identify a trigger signal to start a delayed fMRI acquisition. In this way, the two methods were used together but in an interleaved manner. In real simultaneous applications, like event-related fMRI study, artifacts induced by MRI events on EEG traces represent a substantial obstacle for a right analysis. Up until now, the methods proposed to solve this problem are mainly based on procedures to remove post-processing artifacts without the possibility to control electrophysiological behavior of the patient during fMRI scan. Moreover, these methods are not characterized by a strong "prior knowledge" of the artifact, which is an imperative condition to avoid any loss of information on the physiological signals recovered after filtering. In this work, we present a new method to perform simultaneous EEG/fMRI study with real-time artifacts filtering characterized by a procedure based on a preliminary analytical study of EPI sequence parameters-related EEG-artifact shapes. Standard EEG equipment was modified in order to work properly during ultra-fast MRI acquisitions. Changes included: high-performance acquisition device; electrodes/cap/wires/cables materials and geometric design; shielding box for EEG signal receiver; optical fiber link; and software. The effects of the RF pulse and time-varying magnetic fields were minimized by using a correct head cap wires-locked environment montage and then removed during EEG/fMRI acquisition with a subtraction algorithm that takes in account the most significant EPI sequence parameters. The on-line method also allows a further post-processing utilization.
本研究的目的是开发一种磁共振成像（MRI）伪影的实时滤波程序，以便在连续脑电图（EEG）/功能磁共振成像（fMRI）采集过程中监测EEG活动。在过去几年中，EEG和fMRI联合技术的发展有所增加。初步的“尖峰触发”应用已经可行，因为在这种方法中，仅需要EEG知识来识别触发信号以启动延迟的fMRI采集。通过这种方式，两种方法一起使用，但以交错的方式。在实际的同步应用中，如事件相关的fMRI研究，MRI事件在EEG迹线上引起的伪影是正确分析的一个重大障碍。到目前为止，为解决这个问题而提出的方法主要基于去除后处理伪影的程序，而无法在fMRI扫描期间控制患者的电生理行为。此外，这些方法没有以对伪影的强大“先验知识”为特征，这是避免滤波后恢复的生理信号信息丢失的必要条件。在这项工作中，我们提出了一种新的方法来进行同步EEG/fMRI研究，该方法具有实时伪影滤波功能，其特征在于基于对EPI序列参数相关的EEG伪影形状进行初步分析研究的程序。对标准EEG设备进行了修改，以便在超快MRI采集中正常工作。更改包括：高性能采集设备；电极/帽/电线/电缆材料和几何设计；EEG信号接收器的屏蔽盒；光纤链路；以及软件。通过使用正确的头帽电线锁定环境蒙太奇，将射频脉冲和时变磁场的影响降至最低，然后在EEG/fMRI采集中使用考虑了最重要的EPI序列参数的减法算法将其去除。在线方法还允许进一步的后处理利用。
