以高溫超導射頻線圈平台於7T磁場進行大鼠腦部功能性磁振造影之研究

Abstract

由於近年來人們渴望了解大腦運作的謎團，使得功能性磁振造影(Functional Magnetic Resonance Imaging, fMRI)成為蓬勃發展之科學領域。然而，功能性磁振造影來自血氧濃度(Blood Oxygen Level-Dependent, BOLD)變化產生的訊號非常微弱，極易受雜訊之影響。因此，若能降低功能性磁振造影中的雜訊，其功能性對比和功能性連結的顯著性將大幅增加。 為了改善功能性磁振造影的準確度與可靠度，本研究於7 Tesla (T)動物用磁振造影(Magnetic Resonance Imaging, MRI)系統建立一個新穎的高溫超導射頻表面線圈平台，並將其應用在功能性磁振造影實驗中。因超導體於臨界溫度下電阻極低的特性，使磁振造影系統中之熱雜訊得以大幅下降。 相較於相同大小、形狀之自製銅射頻表面線圈，本論文以高溫超導射頻表面線圈平台獲得約1.8倍的大鼠腦部解剖影像訊雜比增益，於大鼠前掌電刺激功能性磁振造影實驗中，高溫超導線圈亦展現約1.5倍之功能性對比增益。此外，在靜息態功能性磁振造影實驗的時域上也得到近1.4倍的訊雜比增益，且可以觀察到以高溫超導射頻表面線圈平台掃描得到較自製銅射頻表面線圈完整且明顯的大腦運動感覺系統(Sensorimotor System)功能性連結，由於雜訊下降包含運動皮質區(Motor Cortex, M1/M2)、感覺皮質區(Somatosensory Cortex, S1/S2)和視丘(Thalamus)的連結都更加顯著。 本研究結果顯示，當磁振造影系統中之熱雜訊因使用高溫超導射頻表面線圈平台而降低時，不論是影像訊雜比、時域訊雜比、功能性對比與功能性連結，皆有大幅的改善，使得過去受雜訊掩蓋的大腦功能區或連結，能透過使用高溫超導射頻表面線圈平台而更顯著，未來人們將透過此平台對大腦有更進一步的了解。

Recently, the functional magnetic resonance imaging (fMRI) has become a booming technique in the desire of understanding our mysterious brains. However, the blood oxygen level-dependent (BOLD) signal of the fMRI studies is very weak which could be influenced by noise easily. Therefore, if the noise of the fMRI studies could be reduced, the functional contrast-to-noise ratio (CNR) and the significance of the functional connectivity will considerably increase. In order to improve the accuracy and reliability of the fMRI results, the high-temperature superconducting (HTS) radio-frequency (RF) surface coil platform in 7 Tesla (T) animal Magnetic Resonance Imaging (MRI) system served as a novel implementation for the fMRI studies. In the reason, the thermal noise of the MRI system could be reduced for its extremely low resistance attribute under critical temperature (Tc). The results showed that the rat brain anatomy image SNR gain was about 1.8 times by using HTS RF surface coil platform compared to homemade copper RF surface coil of similar size and shape. In the block-design fMRI experiment of forepaws electrical stimulation, the HTS RF surface coil platform demonstrated a 1.5-time functional CNR gain. Besides, the temporal SNR was also improved by using HTS RF surface coil platform with approximately 1.4 times gain in the resting-state fMRI experiment. Furthermore, the functional connectivity of sensorimotor system, including motor cortex (M1/M2), somatosensory cortex (S1/S2), and thalamus, also became much more significant due to the thermal noise reduction as scanned by HTS RF surface coil platform. As shown in the results of this study, the image SNR, temporal SNR, functional CNR, and the significance of the functional connectivity were all improved greatly as the thermal noise was reduced by using HTS RF surface coil platform. The brain functional connectivity would be revealed more accurately using the HTS RF surface coil platform. In the future, more information and knowledge, including reliable brain network causality analysis, would be feasible by using the high SNR HTS RF surface coil platform.