Abstracts

Rationale: Improved noise reduction methods that did not distort the underlying signal could be useful for electroencephalography (EEG) interpretation during high-noise events such as seizures. Recently, a tripolar concentric ring electrode (TCRE) consisting of a central disc, a middle ring, and an outer ring concentric to the disc has been developed to allow highly localized differential TCRE EEG (tEEG) recordings that reduce noise1. We demonstrate the noise reduction effect of TCREs on EEG at the start of a seizure and during a spike-wave burst. The tEEG recordings are compared to simultaneously recorded conventional EEG (cEEG).Methods: A set of 26 conventional disc electrodes was placed on the scalp in the usual manner with collodion and electrode paste. Another set of 20 TCREs was positioned posterior to each conventional disc electrode. The tEEG signals obtained from the TCREs (CREmedical Corp.) were conditioned by a custom high common-mode-rejection preamplifier (CREmedical Corp.). The tEEG from that preamplifier and the cEEG were led to the same Nihon-Kohden jackbox and linked to a common ground. Samples were digitized at 1000 Hz.Results: Figure 1 illustrates the cEEG (top 4 tracings) during a spike-wave burst, compared to tEEG (bottom 4 tracings). Each tEEG channel represents the differential output from adjacent electrodes, with the preamplifier combining the potentials as: 16*(middle ring – central disc) - (outer ring – central disc)1. With both sets of signals band-pass filtered at 1.6-70 Hz, the tEEG channels reproduce the EEG potentials but with less noise than with the cEEG. Figure 2 shows rhythmical ictal activity in cEEG (top 4 tracings) and tEEG (bottom 4 tracings) at the start of a clinically-apparent complex partial seizure. The tEEG shows less muscle artifact and periods of low-amplitude, high-frequency activity not discernable in the cEEG.Conclusions: In conclusion, we found that the tEEG reduces noise and clarifies certain EEG signals. Further experience will be needed to document validity of the recordings in various circumstances and conditions in which they may provide useful supplementary information to conventional recordings. References: Besio WG., Martínez-Juárez IE., Makeyev O., Gaitanis JN., Blum AS., Fisher RS., and Medvedev AV., High-Frequency Oscillations Recorded on the Scalp of Patients with Epilepsy Using Tripolar Concentric Ring Electrodes, IEEE J. Translational Eng. in Health and Med. (J-TEHM), vol. 2, 2014, 10.1109/JTEHM.2014.2332994. Acknowledgements: This work was sponsored by the NSF award IIP-1430833 to Walter Besio of CREmedical Corp. with a subaward to Robert Fisher at Stanford University. Dr. Fisher was also sponsored in part by the Anderson Research Fund for Epilepsy and in part by the Maslah Saul MD Chair.