高精度經顱電刺激系統(HD-tES)，通過穩定的直流電流或交流電流或特殊波形對大腦活動進行調節，是一種非侵入式的神經調節技術。本研究HD-tES系統採用一種帶有小電極的 1×4 高清 (HD) 排列，為四個通道以及一個共同接地點，用於均勻分佈電流，以最小化調製區域。而每個通道可輸出穩定低強度電流(<2mA)，可設置的波形包括DC、AC、pulse、cTBS以及iTBS五種刺激模式，並且運用了低功耗藍芽達到可無線控制的功能，有助於居家穿戴式使用。
硬體的部分使用了12位元解析度的DAC提供電壓輸出，再經由電壓控制電流源將電壓轉換成定電流，每個通道輸出節點設有類比多工器並連接到ADC可有效共用資源並節省空間。韌體的部分主要為控制波形的產生、藍芽資料傳輸、阻抗監控功能以及系統停止安全措施等。軟體結合了GUI使用者控制介面，使用者可以輕鬆控制系統並根據需求調整當前輸入參數，可調整的參數包括波形的選擇、強度大小、頻率大小、占空比大小以及刺激的時間。本研究還開發了阻抗量測功能，刺激前進行測量，以確保電極片與皮膚之間的穩定性，並利用藍芽無線傳輸將數據回傳給使用者，若阻抗值過大或電極片脫落，系統則會回報錯誤。
本研究開發了無線經顱電刺激系統並在經皮迷走神經電刺激實驗得到驗證，實驗中測量心率變化 (HRV) 以反映高頻刺激與低頻刺激以及 cTBS 與 iTBS 的神經調節，在不同刺激模式下對迷走神經有不同的調控效果。HD-tES系統的未來發展可進一步優化，以多通道模組化並提供刺激過程中隨時監控阻抗量測。最終目標是開發多功能的HD-tES刺激系統，可用於臨床上多方面的神經調控技術。

High-definition transcranial electrical stimulation (HD-tES) is a non-invasive neurostimulation technique that modulates brain activity using stable direct current, alternating current, or specific waveforms. In this study, an HD-tES system with a 1x4 high definition electrode array was employed, consisting of four channels and a common ground for uniform current distribution to minimize modulation artifacts. Each channel is capable of delivering constant low-intensity current (<2mA), with five selectable waveform options: DC, AC, pulse, cTBS, and iTBS. The system incorporates bluetooth low energy technology for wireless control, facilitating for wireless usage in future home-care application.
In terms of hardware, a 12-bit resolution digital-to-analog converter (DAC) is utilized for voltage output, which is then converted into constant current through voltage-controlled current sources. Each channel output node is equipped with an analog multiplexer connected to an analog-to-digital converter (ADC), effectively sharing resources and saving space. The firmware controls waveform generation, bluetooth data transmission, impedance monitoring, and system safety measures. The software integrates a graphical user interface (GUI), allowing users to easily control the system and adjust current input parameters according to their needs. Adjustable parameters include stimulation patterns, intensity, frequency, duty cycle, and stimulation duration. This study also developed impedance measurement functionality which can ensure good electrode contact prior to stimulation. Data is transmitted wirelessly via bluetooth back to the user, and the system reports errors if the impedance value is too high indicating the electrode detachment.
The developed HD-tES system was validated in transcutaneous vagus nerve stimulation experiment. The heart rate variation (HRV) was measured to reflect the neuromodulation of high frequency vs. low frequency stimulation as well as cTBS vs. iTBS, demonstrating varying neuromodulation effects under different stimulation patterns. Further development of the HD-tES system can be focused on optimizing multi-channel modularity and real-time impedance monitoring during stimulation. The ultimate goal is to develop a versatile HD-tES stimulation system applicable to various aspects of clinical neurostimulation techniques.

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