臺灣博碩士論文加值系統

本篇論文之研究是利用腦血流，血體積和血氧程度相關功能性磁振造影來探討給予視覺刺激後，相同腦功能區中被活化之體積像素之間血流動力反應(hemodynamic responses)之沉潛時間的變異性(latency variability)。此研究由兩部分實驗所組成。第一部分有六位受試者參與，包含腦血流[利用切片選擇反向回覆(slice-selective inversion recovery, SSIR)技術]和血氧程度相關(BOLD1)兩組實驗。而第二部份則有三位受試者參與，包含血體積[利用非切片選擇反向回覆(non-slice-selective inversion recovery, NSIR)技術]和血氧程度相關(BOLD2)兩組實驗。每一組實驗重複五十次(第一部分)或三十次(第二部份)單一試驗，其中每單一試驗由一秒視覺刺激緊接著十三秒(第一部分)或十九秒(第二部份)十字凝視所構成。從每一個被活化的體積像素中，隨機選擇不同試驗次數來平均，以獲得訊號時間程序(time courses)之不同的對比雜訊比(contrast-to-noise ratio, CNR)。於對比雜訊比之每一特定水平上，對每一體積像素之平均訊號時間程序定義其沉潛時間。隨後計算視覺區中沉潛時間之變異性(△τ)，亦即沉潛時間分布上之標準差。對所有功能性磁振造影技術，當越多試驗次數被平均，所測得的對比雜訊比會越高，而沉潛時間變異則越低。當平均相同試驗次數，由腦血流和血體積功能性磁振造影所測得的對比雜訊比則明顯地比由血氧程度相關技術所測得的對比雜訊比低。對於所有實驗，進一步決定出沉潛時間變異與對比雜訊比(或選擇平均的試驗次數)之間的經驗關係。對比雜訊比在相同的水平下，切片選擇反向回覆與非切片選擇反向回覆兩技術之沉潛時間變異結果均明顯地顯示出低於血氧程度相關之結果。而比較切片選擇反向回覆與非切片選擇反向回覆兩技術之結果，在偵測敏感性與沉潛時間變異性上均沒有顯著的差異。本篇論文研究說明了藉由單一試驗平均可以明顯地改善對比雜訊比，進一步幫助改善功能性磁振造影反應時間的變異。當對比雜訊比在相同的水平下做比較時，切片選擇反向回覆與非切片選擇反向回覆兩技術所測得的沉潛時間變異會低於血氧程度相關之結果，其原因可能是因為此二技術可以得到較好的腦實質區之空間定位的特性。

The latency variability of hemodynamic responses between activated voxels, within the same functional area, was studied by cerebral blood flow- (CBF-), cerebral blood volume- (CBV-) and blood oxygenation level dependent- (BOLD-) based functional MRI (fMRI) using visual stimulations. This study consisted of two parts. The first part included CBF- (using slice-selective inversion recovery, SSIR) and BOLD-based (BOLD1) experiments performed on six subjects, while the second part included CBV- (using non-slice-selective inversion recovery, NSIR) and BOLD-based (BOLD2) experiments performed on three subjects. Fifty (Part I) or thirty (Part II) repeated single trials, each with 1-s visual stimulus followed by 13-s (Part I) or 19-s (Part II) fixation, were conducted in each experimental run. From each activated voxels, different numbers of trials were randomly selected for averaging, in order to obtain signal time courses with different contrast-to-noise ratios (CNRs). At each specific CNR level, the latency of the averaged signal time course was determined on a voxel-by-voxel basis. And the latency variability was then calculated as the standard deviation of the latency distribution within the visual area (△τ). For all the fMRI techniques, the measured CNR increased and the △τ decreased as more trials were averaged. The CNRs obtained by CBF- and CBV-based fMRI were significantly lower than that by BOLD, when the same numbers of trials were averaged. The relationship between the △τ and the CNR (or number of trials selected for averaging) was empirically determined for all the experiments. Under the same CNR levels, both the SSIR and the NSIR results appeared significantly lower latency variations than those obtained from BOLD. No significant differences were observed between the SSIR and the NSIR results, in both sensitivity and latency variability. This study demonstrated that the CNR could be significantly improved by single-trial averaging, which led to improved temporal variability of fMRI responses. When comparing at the same CNR levels, lower △τ for the SSIR and the NSIR than the BOLD may be due to their improved spatial localization to the brain parenchyma.

Title page Page
Approval i
Acknowledgements ii
Abstract (Chinese) iii
Abstract (English) iv
Table of Contents vi
List of Tables vii
List of Figures viii
I. Introduction 1
II. Materials and Methods 6
III. Results 11
IV. Discussion 28
V. Conclusion 33
VI. References 35
Curriculum Vitae 42

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