臺灣博碩士論文加值系統

磁振擴散造影可測量體內水分子擴散現象，而近年來隨著磁振擴散張量造影的發展，大腦神經白質結構及連結得以非侵入性影像的方式具體研究，從磁振擴散張量資料取得的特徵值可用來計算出許多非等向性的指標，進而應用在許多神經纖維結構的量化。目前這些非等向性指標只提供非等向性大小，對於水分子擴散的方向，缺乏有效定量的方法。
本論文首先我們提出了一個新的指標「體素間擴散協調性 (IVDC)」，使用特徵向量計算出空間中每一個體素與其周圍相鄰近的體素在擴散方向的協調性，並可對此指標重建出全腦的圖像。我們顯示了此指標比傳統的非等向性指標對於偵測鄰近間神經纖維的分開更為靈敏，並且它可以提供更多在腦部水分子擴散的資訊。
在臨床應用上，我們針對感覺神經性聽損的病人做了磁振擴散張量造影，比較軸向擴散、側向擴散、平均擴散、非等向性擴散和體素間擴散協調性與正常人的差別，實驗結果發現聽損病人在外側丘系核和下丘兩個位置的非等向性擴散有顯著的減小，其主要原因是由於側向擴散的升高所導致。這些發現將有助於我們更加瞭解聽損病人在神經結構上潛在的損傷。

Diffusion tensor imaging (DTI) is a recent technique that has emerged a sensitive, noninvasive tool for assessing white matter abnormalities in the central nervous system. Several diffusion anisotropy indices have been calculated from the eigenvalues of DTI data. However, current diffusion indices do not provide information on microstructure orientations.
In this thesis, we proposed a novel method for spatially mapping the coherence of eigenvectors within a voxel neighborhood, the InterVoxel Diffusion Coherence (IVDC). We demonstrated that the IVDC index was more sensitive than fractional anisotropy to changes in separation between the fibers and it provides reliable and complementary information on water diffusion in the brain.
For the clinical application, we compared DTI measures of axial diffusivity, radial diffusivity, mean diffusivity, fractional anisotropy and our IVDC along the auditory pathway of patients with sensorineural hearing loss (SNHL) and normal controls. The results showed a high radial diffusivity that consequently led to a decreased fractional anisotropy in the lateral lemniscus and inferior colliculus in SNHL patients. These findings may help improve our understanding of the neuroanatomic basis underlying the deficits in hearing among SNHL patients.

Acknowledgement .....vi
Abstract ...........vii
Publications .......ix
List of Figures.....xii
List of Tables .....xiv
Chapter 1 Introduction 1
1.1 Background 1
1.2 Motivation 2
1.2 Outline 3
Chapter 2 Principles of Diffusion Tensor Imaging 5
2.1 Diffusion MRI 5
2.2 Diffusion tensor 8
2.3 Quantitative diffusion indices extracted by eigenvalues 9
2.4 Visualization of fiber orientation using color encoded FA maps 11
Chapter 3 InterVoxel Diffusion Coherence (IVDC) based on eigenvectors 13
3.1 Introduction 13
3.2 Methods and Materials 15
3.2.1 Theory 15
3.2.2 Simulation studies 18
3.2.3 DTI measurements in human brain 19
3.2.4 Data analysis 20
3.3 Results 20
3.4 Discussion 27
3.4.1 Simulation studies 27
3.4.2 Reconstruction of maps in human volunteers 28
Chapter 4 DTI in patients with Sensorineural Hearing Loss 32
4.1 Introduction 32
4.1.1 Sensorineural hearing pathway in humans 32
4.1.2 Sensorineural hearing loss 34
4.1.3 Purpose of the study 34
4.2 Methods and Materials 35
4.2.1 Subjects 35
4.2.2 MR imaging protocols 36
4.2.3 Data Analysis 37
4.2.4 ROI Statistics 37
4.3 Results 39
4.3.1 Bilateral Profound Hearing Loss 39
4.3.2 Unilateral Profound Hearing Loss 40
4.3.3 Non-profound Hearing Loss 44
4.4 Discussion 47
Chapter 5 Conclusions 51
5.1 Discussions 51
5.1.1 Comparison of the diffusion anisotropy indices 51
5.1.2 Feasibility of IVDC in patients with SNHL 52
5.2 Conclusion 52
5.3 Future works 53
References 55



List of Figures

FIG. 2.1 Schematic illustration of the diffusion-weighted imaging sequence 6
FIG. 2.2 (a) FA map without directional information. (b) Combined FA and directional map 12
FIG. 3.1 Diffusion anisotropy indices at fiber crossover locations, plotted against the separation angle. 21
FIG. 3.2 Images of the calculated indices at the basal ganglia from a healthy subject. 23
FIG. 3.3 FA and IVDC maps of the thalamus in a healthy volunteer. 24
FIG. 3.4 FA and IVDC maps at the level of the middle
cerebellar peduncles and pons. 25
FIG. 3.5 IVDC maps derived from a different volunteer using different ROI sizes. 26
FIG. 4.1 Diagram of auditory pathway. 33
FIG. 4.2 ROIs drawing in a patient with unilateral profound
hearing loss. 38
FIG. 4.3 Avarage DTI measures at the lateral lemniscus 39
FIG. 4.4 Avarage DTI measures in patients with unilateral profound hearing loss (UPHL) 41



FIG. 4.5 Scatter plots of IVDC (a), FA (b) and diffusivities (c) at lateral lemniscus against the measured hearing levels in patients of NPHL group. 45
FIG. 4.6 Scatter plots of IVDC (a), FA (b) and diffusivities (c) at inferior colliculus against the measured hearing levels in patients of NPHL group. 46

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