About this Research Topic
The application of non-invasive imaging methodologies in the study of epilepsy is quite used, but often these techniques are separately considered. Indeed, because of the different nature of the investigation methods, their combination is difficult although would allow to obtain a more specific diagnosis of the epileptic patient. The chance to investigate the pathophysiology of different mechanisms involved in epilepsy and to find different therapeutic approaches is allowed by the used of new multimodal examinations.
Different techniques such as electroencephalography-functional magnetic resonance imaging (EEG-fMRI) coregistration, high density EEG (hdEEG), Arterial Spin Labeling (ASL), Positron Emission Tomography (PET) can be combined to non-invasively map abnormal brain activation elicited by epileptic processes. EEG-fMRI can provide information on the pathophysiological processes underlying interictal activity, since the hemodynamic changes are a consequence of the abnormal neural activity generating interictal epileptiform discharges (IEDs). The source analysis estimates the current density of the source that generates a measured electric potential and it yields a plausible dipole localization of irritative regions. ASL allows the non-invasive estimation of cerebral blood flow values, mapping hemodynamic changes that can occur over the epileptic focus.
Presurgical evaluation of patients with epilepsy is one of the areas where EEG and fMRI integration and electrical source imaging have considerable clinical relevance: in many patients with drug-resistant focal seizures undergoing epilepsy surgery, standard magnetic resonance imaging (MRI) scans fail to visualize a clear epileptic source and thus a preliminary invasive stereo EEG analysis is required. Simultaneous EEG and fMRI recording and Electric Source Imaging (ESI) offer a less invasive alternative, since they provide valuable information to localize the brain regions generating interictal epileptiform activity. From EEG-fMRI and hdEEG registration, insights can be gained into networks associated with interictal epileptic activity. Nuclear medicine techniques, as PET in combination with the [18F]FDG tracer, can also add important information for the accurate localization of the epileptic area in the light of its different metabolic activity in comparison to the other brain tissues. Other neuroimaging techniques, as ASL, are less employed but may offer information complementary to that provided by imaging techniques already in use.
Thus, a multimodal approach to the investigation of brain changes related to interictal epileptiform discharges is needed. In this issue new methods of integration could be utilized to localize the epileptic activity and verify the reliability of the localization. The aim of this topic is to develop methods to integrate the results of these techniques and quantify the performance of new multimodal approaches of analysis compared with the conventional ones in order to improve the identification of activated area. We encourage researchers with expertise in this area to contribute to the research topic.
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