近紅外光譜（NIRS）系統是一種非侵入性光學測量儀器，用於測量組織中氧合血紅蛋白和脫氧血紅蛋白的濃度變化，作為測量腦功能的評估工具。儘管已經開發了各種 NIRS 系統，但本研究的目的是開發一種高性能的嵌入式連續波 NIRS，為臨床應用提供模塊化和可配置的多通道設備。特別是，本研究採用電流調製訊號進行鎖相放大，增強 NIRS 訊號並抑制環境噪聲，但也同時增加電路設計的複雜性。
使用波長為 740 nm 和 880 nm 的兩個 LED 作為光源，搭配矽光電二極管接收組織散射光。兩個波長的光源採用幅度調製技術在固定的時間進行脈衝，並使用鎖相放大器進行解調。鎖相放大有助於從噪聲中提取和過濾光訊號，從而提供更高的訊噪比。總體而言，開發了一種多通道近紅外光譜嵌入式系統，該系統可以同時提供左右半球的大腦活動，每個通道的取樣率為 50 Hz。結合用戶界面，用戶可以輕鬆控制系統並依據實時數據監控中進行調整。分析軟件可以簡單的編輯和計算，顯示血氧濃度的變化。通過執行上臂動脈閉塞實驗驗證本系統的功能，根據先前的研究，可以觀察到血氧濃度的明顯變化。此外在快速手指敲擊實驗下進行了應用於兩個半球前葉的 NIRS 測量。將記錄的數據與市售儀器 NIRScout-1624 進行比較。儘管受試者之間的變異性很高，但平均後的氧合血紅蛋白和脫氧血紅蛋白曲線表現出相似的特徵。
本研究展示了一種多通道 NIRS 設備且在手指敲擊實驗期間的手臂閉塞和前額葉平均血流動力學響應中得到確認及驗證。雖然鎖相放大可以提供更好的抑制環境噪聲，但光強度或接收光電二極管不足以記錄微弱的血流動力學變化。 NIRS 系統的未來發展可以進一步優化，以提高靈敏度並提供遠程記錄，而不會犧牲尺寸和成本。最終目標是開發一種具有無線傳輸功能的高性能和多功能 NIRS 測量系統，可用於研究臨床未滿足需求的大腦和外周肌肉血流動力學變化。
關鍵字:近紅外光譜、鎖相放大、振幅調變。

The near-infrared spectroscopy (NIRS) system is a non-invasive optical measurement instrument used to measure the concentration changes of oxyhemoglobin and deoxyhemoglobin in tissue which has been designed as an evaluation tool for measuring brain function. Although various NIRS systems have been developed, the aim of this study is to develop a high performance embedded continuous-wave NIRS to provide a modular and configurable multichannel device for clinical applications. Especially, current modulation for the lock-in amplification is adopted in this study to enhance NIRS signals and suppress ambient noise without increasing the complexity of circuit design.
Two LED components with wavelengths of 740 nm and 880 nm were used as light sources incorporated with the matched silicon photodiodes to receive tissue-scattered lights. Two wavelengths of light sources were pulsed in a fixed timing with amplitude modulation technique which can be demodulated using a lock-in amplifier. Lock-in amplification can extract the optical signal and filter out noise providing a higher signal-to-noise ratio. The functionality of the system was verified by performing upper arm artery occlusion experiments from which evident changes of blood oxygen concentration can be observed in accordance with previous studies. Furthermore, NIRS measurements applied to the prefrontal lobe of two hemispheres were performed under a quick finger tapping experiment. The recorded data were compared with a commercially available instrument, NIRScout-1624. Although the variability among the subjects is high, the oxyhemoglobin and deoxyhemoglobin curves after averaging exhibited similar characteristics. Overall, an embedded system of multichannel NIRS is developed which can provide brain activities of left and right hemispheres simultaneously at a sampling rate of 50 Hz for each channel. Combined with the user interface, the users can easily control the system and perform adjustments in real-time data monitoring. The analysis software can be simply edited and calculated to display the changes of blood oxygen concentration.
This study demonstrated a multi-channel NIRS device which has been verified and validated in arm occlusion and the average hemodynamic response of the prefrontal lobe during the finger tapping experiment. Although lock-in amplification can provide better immunity to ambient noise, the optical intensity or receiving photodiode is not sufficient to record weak hemodynamic changes. Future development of the NIRS system can be further optimized to increase sensitivity and provide remote recording without sacrificing the size and cost. The ultimate goal is to develop a high performance and versatile NIRS measurement system with wireless transmission which can be used to investigate the brain and peripheral muscle hemodynamic changes with clinically unmet needs.

Keywords: Near infrared spectroscopy system, lock-in amplification, amplitude modulation.

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