EEG is an important modality for many medical purposes. However, the low-amplitude of signals (10-to-100µV) and large number of channels (∼20) raise numerous challenges, including electrode setup (correct placement, skin preparation, sanitation), patient comfort (number of channels, skin abrasion), and robust acquisition (electrode/wire motion artifacts, wire stray coupling). The recent emergence of low-cost, single-use, flexible, pre-gelled electrode arrays, as in Fig. 16.4.1, delivers significant advantages [1]. Today, these are passive, requiring connection to external readout electronics via a many-channel cable. We present the system in Fig. 16.4.1, having similar flexible form factor, but with the following enhancements: (1) embedded low-noise chopper-stabilized amplifiers using amorphous-silicon (a-Si) thin-film transistors (TFTs) compatible with flexible substrates (i.e. low-temperature-processed,  20 EEG channels onto a single interface using TFT scanning circuits, to substantially ease connection with an embedded IC; and (3) an algorithm whereby spectral-energy features, a generic EEG biomarker, are derived directly from the compressed signals (by a conventional CMOS IC). Seizure detection from the extracted features is demonstrated via analog replay of patient EEG through the system.
['Tiffany Moy', 'Liechao Huang', 'Warren Rieutort-Louis', 'Sigurd Wagner', 'James C. Sturm', 'Naveen Verma']
16.4 A flexible EEG acquisition and biomarker extraction system based on thin-film electronics