Abstracts

Rationale: Functional near-infrared spectroscopy (fNIRS) is a non-invasive imaging technique of potential value in the study of epileptic patients (1, 2). Its temporal resolution (20Hz) offers the possibility to study the evolution of hemodynamic changes occurring during seizures. We report here on the hemodynamic behaviour observed in a group of patients with mesiotemporal epilepsy (MTLE). Methods: Patients were diagnosed with MTLE based on multimodal analysis of clinical history, video-EEG monitoring, ictal SPECT, EEG-fMRI, MEG-EEG and intracranial recordings. EEG-fNIRS recordings were obtained using 19 EEG in-house electrodes (EEG video-monitoring; Compumedics, USA) combined with 68 to 120 NIRS channels (ISS, USA) covering the frontal, temporal and parietal lobes bilaterally. Seizure-onset and seizure-end times were respectively defined as the earliest and latest clinical or electrographic evidence of seizure activity. Hemoglobin concentration variations were calculated using the Modified Beer Lambert Law. Results: Four patients with MTLE underwent simultaneous EEG-fNIRS recordings (age 19-49 y-o, 2 males/2 females). A total of 8 complex partial seizures from 3 patients were successfully recorded. All seizures showed significant increase of oxyhemoglobin concentration ([HbO]) compared to baseline starting in the temporal regions and then propagating to adjacent regions. When analyzing the hemodynamic signals during the rising slope (?8s after seizure onset), ipsilateral temporal [HbO] was higher then the controlateral side in 87% of seizures while ipsilateral temporal deoxyhemoglobin concentration ([HbR]) was lower than the controlateral side in 100%. When analyzing the hemodynamic signals at the peak of [HbO] intensity (?40s after onset) and as the seizure propagates, areas of maximal [HbO] changes were congruent with the epileptic region in only 50% of seizures. Time course analysis of [HbR] shows an initial decrease followed by a significant increase (after ?40-60s). The average duration of seizures as determined by EEG was 77s 13s while hemodynamic signals returned to baseline after an average of 181 27s. Conclusions: This study suggests that (a) mesiotemporal lobe seizures are easily detected by continuous EEG-fNIRS; (b) that earliest hemodynamic changes rather than peak changes are more accurate in identifying the region of seizure onset; (c) that the compensatory rise in CBV during seizures may not be enough to respond to the oxygen demand; (d) and that hemodynamic changes take several seconds to return to baseline after the seizure is over.