基於近紅外光譜儀與腦電訊號之腦部活動觀測

Abstract

本論文提出一套同時記錄腦部活動所造成的血氧濃度變化與腦電訊號反應的系統，藉以觀測血氧濃度與腦電訊號的關聯性。此系統具有非侵入式、穿戴方便與操作簡單之優勢，並可長時間量測記錄受測者腦部的血氧與腦電訊號變化。 為了縮短訊號傳遞路徑，並減少訊號傳遞損耗，本系統設計了前端類比放大電路，並將其置於感測探頭之中，在訊號傳輸前先進行預處理放大，提高訊號訊雜比。此晶片採用TSMC 0.18 µm 1P6M CMOS標準製程，而前端放大電路中使用虛電阻元件與電容構成一高通濾波器，並且實現0.06 Hz的低頻極點，用來濾除電極-皮膚間的直流偏移成分，避免放大器失真或飽和，且單一通道功耗僅18.3 µW。接著，將前端類比放大晶片與後端血氧濃度與腦電訊號同步量測系統整合，利用閉眼與憋氣、心算和握拳實驗來驗證系統的可靠度，並同步記錄血氧濃度與腦電訊號的變化，觀測在不同實驗狀態下，兩種訊號的關聯性。 經由上述實驗，可驗證本系統能有效同步記錄不同受測者腦部的血氧變化與腦電訊號反應。接著觀察到每次刺激事件發生時，腦電訊號會比血氧濃度訊號較快反應，但血氧濃度變化訊號會比腦電訊號持續較長時間。故可說明，當腦部神經活動時，表面的腦電訊號先反應，深層的血氧濃度訊號較慢反應，但表面的腦電訊號反應完後，深層的腦微血管還是持續有血液流動而造成血氧濃度訊號持續反應，並且透過腦電訊號來輔助解釋血氧濃度的變化。

This study proposed a brain activity monitoring device with simultaneous hemoglobin concentration and electroencephalography (EEG) measurement to figure out the relation between hemoglobin concentration and EEG on brain. The proposed sensor device is non-invasive, wearable and easy to use for long-term brain activity recording. To shorten signal transmission path and reduce signal loss, this work designed a low power consumption front-end amplifier (FEA) embedded into sensor devices to amplify and filter signal before post processing system to promote signal-to-noise ratio. The FEA was designed and fabricated with TSMC 0.18 μm 1P6M CMOS standard process. By using pseudo-resistor elements and capacitors to build a high-pass filter, the FEA can achieve a low frequency pole at 0.06 Hz and 37.6 dB gain. It can remove skin-electrode interface DC offset and avoid FEA saturation or distortion and only needs 18.3-µW power consumption. Moreover, the sensor device with the FEA was integrated with post blood oxygen and EEG recording system to verify feasibility of the system by the experiments of eyes closing, breath holding, mental arithmetic and hand grasping, and to discuss the relation between brain blood oxygen and EEG. According to the experimental results, EEG signal response to event stimulations is faster than oxyhemoglobin and deoxyhemoglobin concentration response. The results show that EEG signal responses immediately and the concentration of hemoglobin responses lastingly a period of time while stimulating.