Abstracts

Rationale: High resolution dense electrode EEG (HR-dEEG) consists of 128 or 256 channel scalp EEG recording using DC amplifier with wide range frequency range between 0.1 to 150 Hz.  Greater number of scalp surface electrodes  and shorter inter-electrode distance, 2 cm, is factor to improve special resolution, so that it allows us to narrow down the area of irritable zone. Methods: In the HR-dEEG system (EGI by Eugene, OR), 128 electrodes were placed with normal saline contact by a convenient cap system.  Average inter-electrode distance is 1.8-2.0 cm while the conventional 10-20 system has 6.5- 7 cm.  10-10 system has 3-3.5 cm.  LFF and HFF settings were 100-150 Hz and 0.1 -1.0 Hz respectively. Sampling frequency was 1000 Hz. The recording montage was developed by the author for this specific 128 channel recording based on basic “double banana” montage as seen in picture insert.Three patients of chronic seizure disorder.  Interictal outpatient EEG was recorded for 30 minutes.  Three scalp recorded 128 channel EEG are presemted to demonstrate (1) evidence that HFO can be recorded distinguished from artifacts by known basis electrophysiology;  (2) infra-slow delta activity; (3)   narrowed electrical field and higher spatial resolution. Results: FINDINGS:Case #1:  It demonstrates dEEG capability which appreciated focal ISD and electrographic beta which evolved into gamma/HFO frequency range with clear delineated electrical field.  This is a demonstration that HFO can be seen in scalp recording evidenced by basic EEG electrophysiology.  The highest frequency which may be reasonably seen was approximately 120 to 150 Hz.Case #2 : dEEG demonstrates feature of sustained electrographic seizure in gamma frequency range up to 33 Hz, but having definite electrical field in nearby electrodesCase #3 : dEEG demonstrates multifocal electrographic seizure distribution, suggestive of existence of multiple epileptogenic networks without resorting invasive EEG recordings. Conclusions: HR-dEEG has technically uncomplicated in recording needing reasonable training, and convenient by cap system.  It does not require collodion for scalp fixation.  It shows better special resolution, and high fidelity in wide frequency range.  DC amplification allows us to identify wide range cortical activity from Infra-Slow Delta activity to low frequency range of HFO up to 120 Hz, and better localization of  abnormal discharge patterns by higher spatial resolution.  Funding: No funding for this study.