Abstracts

Rationale: Electroencephalography (EEG) allows long-term monitoring of the brain's electrical activity notably abnormal epileptiform discharges and seizures. However, it does not provide information on cerebral blood volume (CBV) and oxygenation. Functional near-infrared spectroscopy (fNIRS) is a relatively novel technique (based on the same principles underlying pulse oximetry) which allows one to monitor non-invasively and continuously superficial cerebral hemodynamic changes [including oxygenated hemoglobin (HbO), reduced hemoglobin (HbR) and total hemoglobin (HbT) changes]. Combining fNIRS and EEG for brain monitoring could provide useful complementary information. Unfortunately, current commercial fNIRS systems are bulky, lack portability, provide poor spatial coverage, and lack simultaneous EEG recordings. Our goal was to develop a light, portable, wireless and user-friendly simultaneous fNIRS-EEG system with high channel count for long-term monitoring of epileptic patients. Methods: The EEG-fNIRS system is composed of a) a helmet made of elastic fabric; b) 32 light emitting diodes (LED emitters ) (2 wavelenghts : 735 nm and 850 nm); c) 32 avalanche photodiodes (APD detectors); d) 32 EEG electrodes; e) a control module composed of 3 printed circuit boards (PCB); f) a transmission system through Bluetooth (BT) or Universal Serial Bus (USB) cable; and g) a personalized graphical user interface (LabVIEW). The prototype was tested on three healthy subjects using a visual task and analyzed with Vision Analyzer 2 (Brain Vision, Munich) software and a MATLAB-based graphical user interface program (HomER). Results: The system weighs 650 g, measures 12x9x7 cm³, can operate on battery supply for up to 24h, and is adapted to include 32 EEG channels and fNIRS 32 emitters and 32 detectors (providing up to 128 channels for full head coverage). In all 3 subjects, our prototype was able to visualise the expected rise in HbO/HbT and decrease in HbR over bilateral occipital areas following the visual stimulus. The EEG signal was of good quality. Conclusions: Preliminary results indicate that our light portable EEG-fNIRS can be used to detect simultaneous electrical and hemodynamic information. Recordings in the epilepsy monitoring and neurological intensive care units are currently underway.