256-channel electroencephalographic data-acquisition system for electrical source imaging

vi256-CHANNEL ELECTROENCEPHALOGRAPHICDATA-ACQUISITION SYSTEM FOR ELECTRICAL SOURCE IMAGING(Ph.D.Thesis)Ali Bülent UŞAKLIGAZİ UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYDecember 2006ABSTRACTThe neurons of the human brain generates electrical activities due toauditory, visual or somatosensory stimuli. The activities createelectrical potential on the scalp (0.5-70 Hz and <300 µV)(electroencephalography, EEG). In this thesis, to increase theperformance of electrical source localization by using more channelnumbers, a novel 256-channel EEG data-acquisition system (EEGDAS)is designed and realized. Design strategy is based on DC coupling,24 bit analog to digital conversion and universal serial bus. Themotivation behind the design and realization of a novel 256-channelEEG system is to obtain more accuracy in electrical source localization.This helps finding more accurately the epileptic foci or other anomaliesin the human brain. Analog signals coming from electrodes areamplified (gain 13.8) and converted with 24-bit sigma delta technologyanalog to digital converter. Data is transferred via USB at the rate of144 Kbyte/sec to temporary storage and then 1 Mbyte/sec to thecomputer. The sampling rate of the system is 140 Hz. The system canproduce auditory click signal for the head phone or a trigger signal forthe external stimulator at about one second interval. The commonmode rejection ratio of the system is measured as 102 dB and electricalnoise is 1.76 μV (rms). The dynamic range of the system is found to bevii108 dB. 256-channel spontaneous EEG and auditory evoked potentialrecordings, averaged signals and brain maps were obtained in thisstudy. EEGDAS can operate user friendly and each point of thehardware and software can be reached for any modification to conductdifferent types of EEG measurement experiments. Performance testsand signal recordings show that the system can be used for theelectrical source imaging in the human brain.Science code : 704.3.013Key words : Electroencephalography, multi-channel data acquisition,bio-potential measurements, performance testsPage number : 212Adviser : Prof.Dr. Nevzat G. GENÇER