Real-time MR artifacts filtering during continuous EEG/fMRI acquisition.
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.
Garreffa
G
G
Department of Physics, University of Rome, La Sapienza, Rome, Italy.
Carnì
M
M
Gualniera
G
G
Ricci
G B
GB
Bozzao
L
L
De Carli
D
D
Morasso
P
P
Pantano
P
P
Colonnese
C
C
Roma
V
V
Maraviglia
B
B
D000465:Algorithms; D016477:Artifacts; D017352:Echo-Planar Imaging / Q000379:methods; D004569:Electroencephalography / Q000379:methods; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D012815:Signal Processing, Computer-Assisted