Simultaneous eeg-fmri with epi and spiral k-space trajectories. Clinical application in fixation-off epilepsy

Laburpena

Acquisition of electroencephalogram (EEG) during functional Magnetic Resonance Imaging (fMRI) provides, non-invasively, the simultaneous capture of cerebral hemodynamic response as well as the registered electric cerebral activity on the scalp. This new multimodal technique provides an ideal combination of the excellent spatial resolution of fMRI with the millisecond temporal resolution of EEG. However, there are four major challenges related to this multimodal technique, which must be addressed to improve the simultaneous combination of these two neuroimaging techniques: o EEG instrumentation and patient safety o EEG signal quality preservation because the simultaneous acquisition inside the MR scanner introduces several different and specific types of EEG artifacts, among them, the gradient artifact and the cardiac pulse-related artifact. o MR images SNR and CNR that will be dependent on the used fMRI pulse sequence o Interrelation of both signals is challenging because the electrical signals measured by the EEG system and hemodynamic signals measured by the MR scanner come from different physiological events whose coupling is still not fully understood. From the point of view of the clinical applications of this multimodal technique, one of the most interesting ones is the study of the abnormal electrical activity in patients with epilepsy. This work differs from most applications of fMRI because the stimulus is internally generated, in a random and infrequent way in most of the cases. In this thesis project, it is aimed to develop an improved experimental setup for simultaneous EEG-fMRI and test the influence of different key acquisition strategies: the influence of using different k-space trajectories fMRI pulse sequences and the impact of synchronization. The first necessary step for these aims consisted of the development of a modified spiral EPI pulse sequence from its basic form in order to improve the quality of both signals: EEG and fMRI. On the other hand, and in a more practical part of this PhD thesis, the use of an improved simultaneous EEG-fMRI experimental setup and a proper preprocessing and analysis of both kinds of data was applied in a clinical study. A rare epileptic syndrome known as Fixation-off Sensitivity (FoS) Cryptogenic Generalized Epilepsy (CGE) was examined. This syndrome has not been intensively studied due to scarce number of cases and limitations of other techniques; in fact, there are only three previous works in the literature where FoS discharges were examined with simultaneous EEG-fMRI. This thesis project aims to obtain novel results in the study of Fixation-Off CGE patients using simultaneous EEG-fMRI.