高溫超導動物腦磁儀系統開發
Development of High-Tc Superconducting Magnetoencephalography System for Animals
In this project, high-Tc Superconducting Quantum Interference Device (HT SQUID) arrays were fabricated to establish a magnetoencephalography (MEG) system for the application on studies of animal MEG. The fabrication challenges the limit of the HT SQUID features that can be comparable to those of traditional low-temperature superconducting SQUIDs with high sensitivity and low noise characteristics to reduce dependence on expensive liquid helium. It is expected to break through the limits of the crosstalk effect on the SQUID array, and increase the spatial resolution to less than 5 mm, which is comparable to the spatial resolution of ~ 15 mm for the current low-Tc superconducting MEG system. In addition, the HT SQUID MEG system will be applied on the studies of animal neuropathy mechanisms to make up the current researches with electroencephalography (EEG) systems. By improving the positioning of the measuring end of the MEG system and the imaging of the back-end data inversion, the auditory brain response induced by the organism rat with a given sound stimulation was observed. According to the relationship between the intensity and position of the ECD from the observation of the P9 waveform induced by auditory stimulation, it can be shown that the brain has strong control over the auditory stimulation response. This confirms the correctness and feasibility of this system measurement. Moreover, the improvement of the positioning calibration and inversion algorithm is applied for animals which require high spatial resolution. The intensity and position of the equivalent current dipole (ECD) are deduced from the inversions of the iso-field contour mapping. The minimum-norm estimation (MNE) and the minimum range after introducing the parameters with source iteration of minimum norm (SIMN) are compared. It is found that SIMN can get more concentrated and accurate data than that by using MNE. The following figure shows the schematic and actual diagram of the scanning HT SQUID magnetic detection system. The HT SQUID device is immersed in the liquid nitrogen in the Dewar. In order to reduce the interference of the surrounding environment, the whole system was taken into account of the background noise from the metal materials, and the liquid nitrogen storage tank was designed to be fixed on the wooden frame and placed in the shielded house for detection. The sample can be placed on the lower stepping motor and controlled by the computer program to perform the magnetic-signal acquisition in a two-dimensional space.
schematic and actual diagram of the scanning HT SQUID magnetic detection system
本計畫以高溫超導量子干涉元件(High-Tc Superconducting Quantum Interference Device, HT SQUID)陣列製作腦磁圖（Magnetoencephalography，MEG）量測系統，應用於動物腦磁圖研究，製程將挑戰 HT SQUID 特性之極限，能與傳統低溫超導 SQUID 高靈敏、低雜訊特性相媲美，以降低對昂貴液態氦之依賴。且突破 SQUID陣列串音效應(crosstalk effect)之極限，提高空間解析度至 5 mm 以下，相較於目前低溫超導 MEG 之~15 mm 空間解析度。此外，將高溫超導 SQUID MEG 應用於動物腦神經病變機制研究，彌補現今以腦電圖研究之不足。藉由改進 MEG 系統量測端的定位以及後端資料反演算的成像，觀測生物體大鼠在給定聲音刺激後，誘發的聽覺大腦反應。從觀測聽覺刺激誘發反應的 P9 波形，觀測 ECD 的強度以及位置之間的關係，可以說明對大腦對於聽覺刺激反應有較強的主控性，並證實此系統量測的正確性及可行性。此外，定位校準和反演算法的改進適用於需要高空間分辨率的動物。等效電流偶極子（ECD）的強度和位置是從等場輪廓映射的反演推導出來的。 比較了最小範數估計（MNE）和引入最小範數源迭代（SIMN）參數後的最小範圍結果發現，與使用 MNE 相比， SIMN 可以獲得更集中，更準確的數據。下圖為本研究成果之掃描式 High-Tc SQUID 磁檢測系統的示意圖與實際圖，High-Tc SQUID 元件浸泡在杜瓦瓶中的液態氮裡，為了降低周圍環境的干擾，整個系統考慮到金屬材料的背景雜訊影響，液態氮儲存槽固定在木架上，並放置屏蔽屋中做使用，樣品放置在下方步進馬達上透過電腦端程式控制，可以進行二維空間的磁訊號擷取。
掃描式High-Tc SQUID磁檢測系統的示意圖與實際圖