Gradient Noise Reduction in EEG Acquired During MRI Scan

Lee, H R; Lee, H N; Han, J Y; Park, T S; Lee, S Y

Abstract

PURPOSE
Information about electrical activity inside the brain during fMRI scans is very useful in monitoring physiological function of the patient or locating the spatial position of the activated region in the brain. However, many additional noises appear in the EEG signal acquired during the MRI scan. Gradient induced noise is the biggest one among the noises. In this work, we propose a gradient noise reduction method using the independent component analysis (ICA) method. MATERIALS AND METHODS: We used a 29-channel MR-compatible EEG measurement system and a 3.0 Tesla MRI system. We measured EEG signals on a subject lying inside the magnet during EPI scans. We selectively removed the gradient noise from the measured EEG signal using the ICA method. We compared the results with the ones obtained with conventional averaging method and PCA method. RESULTS: All the noise reduction methods including the averaging and PCA methods were effective in re-moving the noise in some extent. However, the proposed ICA method was found to be superior to the oth-er methods. CONCLUSION: Gradient noise in EEG signals acquired during fMRI scans can be effectively reduced by the ICA method. The noise-reduced EEG signal can be used in fMRI studies of epileptic patients or combinatory studies of fMRI and EEG.