功能性近紅外光譜 (fNIRS) 系統是一種非侵入性的神經光學測量儀器，它利用近紅外光對氧合血紅蛋白 (HbO) 和去氧血紅蛋白 (Hb) 的高吸收率來推估它們在大腦中的濃度變化，用來評估大腦局部皮質對於神經活動的響應功能。通常血流動力學反應的變化在低頻段進行分析。本研究的目的是開發一種高頻率的NIRS系統來檢測更高頻率的訊號，從而提供更深入的分析。
光極模組由兩個波長為760 nm和850 nm的LED光源組成並配有三個PIN光電二極管的柔性探頭，用於接收穿過組織後衰減的光訊號。我們定制的連續波NIRS系統的每個通道的採樣率為250 Hz，與一般的連續波NIRS系統相比，更高的採樣率提高了時間分辨率，並提供了高頻信號分析的潛力。fNIRS評估大腦功能的方式是基於局部血紅蛋白濃度變化的估計值，分析過程中去除了大部分高頻訊號，以消除其他生理訊號的影響，我們還可以嘗試使用我們的NIRS系統分析高頻訊號。
本研究透過在指尖測量的PPG訊號和阻塞期間前臂內側肌肉和等長收縮期間二頭肌的血流動力學反應，驗證了我們的NIRS系統對血液容量變化的反應。還記錄了手指點擊和呼吸控制期間的前額葉的血流動力學反應。然後將測得的訊號與商用地NIRScout-1624進行比較。此外，使用0.5 Hz到10 Hz的帶通濾波器對呼吸控制期間的訊號進行高頻分析，將PPG訊號與低頻的血流動力學訊號分離。
我們的研究展示了一種高頻連續波NIRS系統，用於紀錄肌肉組織和前額葉中的血流動力學反應，並能提取後續的PPG訊號。這些NIRS訊號可以用於未來的大腦神經調節和肌肉活化的評估。未來可以進一步增強微弱的血流動力學訊號並提供穩定的無限數據傳輸，開發出多樣化的探頭來滿足臨床上的應用。

The functional near-infrared spectroscopy (fNIRS) system is a non-invasive neuro-optical measurement instrument that utilizes the differential absorption rates of near-infrared light on oxyhemoglobin (HbO) and deoxyhemoglobin (Hb) to estimate their concentration changes as a function of the brain. As a tool for assessing the function of local cortical responses to neural activity. The changes in hemodynamic responses that are commonly analyzed in the low-frequency band. The purpose of this study is to develop a high-frequency NIRS system to detect the NIRS signals at higher frequency that could provide more insight analysis.
The optode module composed of two LEDs light source with wavelengths of 760 nm and 850 nm. A flexible optical probe of three PIN photodiodes was designed to receive the attenuated light through the tissue of different path lengths. The sampling rate of each channel of our custom-made CW-NIRS system can reach 250 Hz by careful control of analogue front end time sequence. Compared with the commercially available CW-NIRS system, the system with increased sampling rate could provide the potential of high-frequency signal in addition to low-frequency of hemodynamic response based on NIRS recordings of hemoglobin concentration changes.
This study verified our NIRS recordings from muscle and brain hemodynamic responses. First, the experiment was designed to record changes in blood volume by measuring the Photoplethysmography (PPG) signal at the fingertip and hemodynamic responses of forearm muscle during occlusion and bicep muscle during isometric contraction. The hemodynamic responses of prefrontal lobe during finger tapping and respiratory control were also measured and processed to remove the undesired physiological signals. The signal during respiratory control was filtered using a 0.5-10 Hz bandpass filter, to separate PPG signals from low-frequency hemodynamic signal.
Our study demonstrated a custom-made high-frequency CW-NIRS system for recording hemodynamic responses in muscle tissue and prefrontal lobe which can extract hemodynamic response and subsequent PPG signals. These NIRS measurements can be utilized for future assessment of brain neuromodulation and muscle activation. Future development can further enhance the weak hemodynamic signals and provide stable wireless data transmission for versatile probe design to meet the clinical applications.

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