大腦及周邊連結之功能性磁振造影初探

Abstract

磁振造影（MRI）在醫學上用途廣泛。臨床醫療中，主要用於偵測身體各部位病灶，而「功能性」造影則越發用於大腦科學研究。神經系統遍佈全身，腦部和脊髓屬於中樞神經，而其餘為周邊神經。解剖以及生理功能上，兩者密切關連，並且與其他系統譬如心血管循環緊密互動。有關中樞及周邊神經的研究相當廣泛，但過往研究多著重個別變化，而整合性研究是近年來新興趨勢。本計畫以建立整合中樞及周邊神經系統研究之平台為出發點，期待以同步形式，研究跨系統功能。 本研究建立首度可以同時獲取腦部及週邊組織影像之結構與功能磁振造影平台。在此平台，受試者採取新受檢姿勢，也就是「手臂過頭」檢查姿勢（Arm-Over-Head, AOH position），此姿勢運用現有的磁振造影技術與線圈，同時取得腦部及手臂的影像。在已建立之磁振造影平台，我們測試了各種不同造影參數，獲得判讀上可接受的結構與功能影像品質。同時，一併測試受試者對於此種姿勢的耐受度。在此實驗中，所獲取的是頭部及右側手臂的影像。 在決定最適宜造影參數，同時也確定受測者耐受度後，我們讓受試者執行上手臂屈曲運動想像之實驗，以探討此種活動對中樞及周邊神經系統的擾動，並藉此研究兩者關聯性的空間與時間變化。上手臂屈曲運動想像包括了「右側上手臂屈曲運動想像」以及「左側上手臂區曲運動想像」。所採用分析方法，主要為獨立成份分析（Independent component analysis, ICA）與複雜神經網路分析（complex network analysis）。分析顯示，在執行自發運動想像時，不論是「右側上手臂屈曲運動想像」以及「左側上手臂區曲運動想像」，腦部與右側上臂處觀測到具有信號共振現象的區域包括預設模式網路（Default mode network, DMN）、感覺運動網路、以及視覺網路。以經過驗證大腦磁振造影神經科學的角度觀之，此種現象，應不只是局部血液循環「雜訊」干擾大腦之呈現（bottom-up noise），合理包括中樞神經延伸至周邊神經之單向甚是雙向細微調控（top-down regulation）。此外，檢視6位受試者的平均資料，發現主要在感覺運動網路，「左側上手臂區曲運動想像」時的信號共振現象較「右側上手臂區曲運動想像」來得明顯，此差異達統計意義（未經校正p值<0.05）。 建構此平台提供研究潛在遍佈全身神經及生理網路現象、及其間相關性的科學性方法。可能的應用包括：協助了解神經系統功能性網路之機轉與本質，作為探討身體各器官系統網絡交互作用的起始基礎，作為輔助診斷的參數，疾病進程的指標，以及各項生理訓練或是治療對於整體生理功能的影響。

Magnetic resonance imaging (MRI) has multiple applications in medicine. In clinical medicine, it is mainly used to detect lesions in various parts of the body, while 'functional' imaging is more frequently used in brain science research. The nervous system is spread throughout the body. The brain and spinal cord belong to the central nervous system, while the rest belong to the peripheral nervous system. Anatomically and physiologically, the two systems are closely related and interact with other organ systems such as cardiovascular circulation. Researches on the central and peripheral nervous systems are quite extensive, but previous studies mainly focused on “respective” changes. This study intends to establish a platform that integrates the research of the central and peripheral nervous system and looks forward to studying cross-system functions. This research establishes the first structural and functional MRI platform that can simultaneously obtain images of the brain and the periphery. On this platform, the subject adopts a new examination posture, which is the 'Arm-Over-Head (AOH)” position. This posture uses currently available MRI technology to obtain images of the brain and arms at the same time. Under this platform, we tested various imaging parameters to obtain acceptable structural and functional image quality for further analysis. The tolerability of the AOH position is acceptable. In this platform, the brain and “right” upper arm imaging were obtained simultaneously. After deciding the optimal parameters, motor imagery tasks (imagery right elbow flexion and imagery left elbow flexion) composed of 6-cycle on-off blocked design with self-paced rhythmic elbow flexion were performed to test the possible brain-periphery oscillations. Independent component analysis (ICA) and complex network analysis were used. It is demonstrated during motionless motor imagery tasks there existed possible brain-body blood oxygen level dependent (BOLD) oscillations connecting especially arm flexors to default mode, vision, and sensorimotor networks in the brain. These oscillations exist during both imagery right elbow flexion and imagery left elbow flexion. For the functional connectivities between the right arm flexor and especially sensorimotor networks, there was a positive effect of “imagery left elbow flexion” on them, i.e., brain to right arm functional connectivities seemed to be stronger with imagery left sessions, and the uncorrected p-value was < 0.05. From the current state-of-the-art perspective of neuroscience, this phenomenon should not be solely explained by the 'bottom-up noise' of local blood circulation, but may also be explained by the unidirectional or bidirectional regulation of the central nervous system to the peripheral nervous system. The construction of this platform provides a scientific method for studying the potential of neural and physiological network phenomena throughout the body and their correlations. Possible applications include: assisting in understanding the mechanism and nature of the functional network of the nervous system, as an initial basis for exploring the network interaction of various organ systems of the body, as a parameter for assisting diagnosis, an indicator of disease progression, and various physiological training or the effect of treatment on the overall physiological function.