同調分析在功能性磁振造影與平靜狀態功能性磁振造影上之應用

Application of Coherence Analysis Method on fMRI and Resting-state fMRI

陳家芳(Chia-Fang Chen)

指導教授 ： 陳志宏

國立臺灣大學/電機資訊學院/電機工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.10359

摘要

近年來以功能性磁振影像研究大腦內在功能性連結是一門除了實質上結構性的連結與有效連結外的新方向。相關係數分析法已經廣被應用在功能性連結的研究上。功能性連結的基本假設是大腦中相關區域在同樣的時間有著高度的線性時序相關性‚這些具有高度線性時序相關性的局部區域從過去的實驗結果歸納出同歩低頻震盪信號存在於這些功能性連結的區域‚這個同步低頻震盪的頻率一般認為是在0.1Hz以下‚也普遍的被認為是大腦內部神經連結一個可能的證據。
本篇論文採用同調性分析的方法‚探討頻率上相關性的方法研究一般功能性影像與平靜狀態功能性的影像‚並藉由同調性分析裡交互頻譜密度函數來研究信號之間相位差的問題。
論文中先採用仿體測試搭配ROC(Receiver operating characteristic)曲線分析比較相關係數法與同調性分析法在Bruker MedSpec 3T system上的表現‚再根據同調性分析法的優點分析功能性的影像與平靜狀態功能性影像。本研究設計一組相位差功能性實驗‚再以同調性分析法找出相關區域的相位差。另外‚本篇論文成功的找出在低頻部分不同頻率(0.025Hz與0.08Hz)的同調係數映射圖與相位映射圖,結果顯示低頻部分不同的頻率有著不同表現的映射圖。而且目前作功能性連結相關的研究為了避免生理雜訊混疊到所要觀察的低頻信號‚TR(repetition time)必須縮短到400ms(有效頻寬1.25Hz)以下‚導致影像解析度的不足。未來的工作勢必朝這方面進行。

關鍵字

功能性磁振造影 ； 同步低頻震盪 ； 功能性連結 ； 平靜狀態功能性影像

並列摘要

A new direction in studying interregional functional connectivity using magnetic resonance imaging (fMRI) in addition to structure connectivity and effective connectivity. The basic hypothesis of functional connectivity is the high linear temporal relationship in the relevant information about the interactions of brain regions at the same time. The relevant brain regions with high linear temporal relationship induce the result that synchronicity of low frequency fluctuations in functional related regions. Using functional connectivity MR(fcMR) imaging‚research workers identified very low frequency (<0.1 Hz) fluctuations in the signal of the resting brain‚revealing a high degree of temporal correlation‚and is a evidence of the existence of neuronal connections characterizing a widespread cortical network.
By adopting relationship in frequency domain‚ coherence analysis method is presented on the thesis for conventional fMRI and resting-state fMRI. Otherwise‚ I use cross spectral density function in the coherence analysis method to discuss the phase delay and phase lead. The thesis adopts phantom tests with ROC (Receiver operating characteristic) curve analysis to compare cross correlation analysis method with coherence analysis method on Bruker MedSpec 3T system‚ and according to the advantage of coherence analysis method to analysis conventional fMRI and resting-state fMRI. This reseach designed a phase delay fMRI experiment‚ and used coherence analysis method to find the phase delay. This thesis successfully discover the coherence maps and phase maps on the different frequency (0.025Hz and 0.08Hz), and the result shows different frequency in the very low frequency (<0.1Hz) perform distinct maps. Recently for the purpose of excluding physiological noise aliasing to the low frequency signals which we want to observe‚ TR(repetition time) should be shortened to the value under 400ms (effective frequency band is 1.25Hz). This will lead to not enough special resolution which is an essential topic for future study.

並列關鍵字

synchronous low frequency fluctuations ； BOLD ； resting-state fMRI ； functional connectivity ； functional MRI

參考文獻

[1] Biswal BB, Van Kylen J, Hyde JS.”Simultaneous assessment of flow and BOLD signals in resting-state functional connectivity maps‚” NMR Biomed. 1997 Jun-Aug;10(4-5):165-70.

[2] Ogawa‚ S.‚ Tank‚ D.W.‚Menon‚ R.et al.‚”Intrinsic signal changes accompanying sensory stimulation: Functional brain mapping with MRI.”Proc. Natl. acad. Sci. 89‚5951-5955‚1992

[3] Leopold DA‚ Murayama Y‚ Logothetis NK‚”Very slow activity fluctuations in monkey visual cortex: implications for functional brain imaging.” Cerebral Cortex Apr 2003;13:422–433.

[4] Nikos K. Logothetis, Jon Pauls, Mark Augath, Torsten Trinath & Axel Oeltermann‚” Neurophysiological investigation of the basis of the fMRI signal.”‚NATURE

[5] Scott J Peltier‚ Thad A. Polk‚ Douglas C. Noll‚”Detecting low-frequnecy functional connectivity in MRI Using a self-Organizing Map (SOM) Algorithm‚”Human Brain Mapping 20:220-226(2003)