本論文的目標是研究使用”非水抑制”對人體內的磁振頻譜作代謝物定量。此方法在某些情況下是必須的，例如在嚴重的磁場不均勻處以及動態掃描，此時水抑制不可行。同時，此方法便於針對代謝物濃度定量作絕對定量。
第一，我們使用非水抑制的方法來修正時間上的相位與頻率飄移。這個非水抑制的方法能顯著改善人體磁振頻譜品質，但不需延長掃描時間。我們成功地將此修正方法應用在體內的磁振頻譜。
第二，針對體內的非水抑制的頻譜定量，我們提出時域上的濾波-對角化的方法。根據模擬，此方法與其他時域方法有類似的穩定性與穩健性。並且，我們將此方法應用在仿體實驗與人體內實驗，顯示此方法適合應用於人體的磁振頻譜，並且也適合應用在非水抑制的磁振頻譜。The purpose of this thesis is to investigate the potential to acquire in vivo metabolic information using non-water suppressed magnetic resonance spectroscopy (NWS-MRS) technique. The use of NWS MRS is necessary when water suppression is not applicable for serious susceptibility and motion. As well, NWS MRS is potentially convenient for absolute metabolites concentration quantification.
First, we correct the temporal phase and frequency drifts during MRS scans using internal water signal in the NWS MR spectra. The use of NWS method significantly improves the quality of in vivo MRS without prolong scan time. The successful application of the developed techniques to high quality in vivo MRS is demonstrated.
Second, a time–domain MRS fitting method “filter-diagonalization method” (FDM), is proposed for the quantification of “non-water suppressed” MR spectra. Based on our simulation studies, the stability and robustness of FDM method is comparable to other time-domain methods. Furthermore, the phantom and in vivo experiments showed that the FDM enables the quantification of metabolic information in water suppressed (WS) and NWS MR spectra respectively.Abstract……………………………………………………………….…1
中文摘要………………………………………………………….……...2
Chapter 1 Introduction..……………………………….……..…….......3
Chapter 2 Non-water suppressed MR Spectroscopy and its Quantification algorithms……………………………………………...........7
2.1. Non-water suppressed MR Spectroscopy (NWS MRS) ……....7
2.1.1. The advantages of NWS MRS ………………………………............7
2.1.2. The difficulties and challenges of NWS MRS…………………........11
2.2 Implementation of Time-Domain Methods for NWS-MR spectrum: the phantom study……………………………...…...16
2.3 Review of frequency-domain methods and time-domain methods for MRS quantification……………………………………………..........17
2.3.1 Frequency domain methods: ……………………..………..…...........17
2.3.2 Time-domain methods………………………….………..……..........18
2.3.3 The time domain fitting algorithms……………….………..………...20
2.4 Quantitative NWS MRS: the Phantom Study………………….26
2.5 Results and Discussion ………………………………………..29
Chapter 3. Correction of motion related signal loss in MR spectroscopy ………………………………………….….30
3.1. Introduction……………………………………………………30
3.2 Correction methods for motion induced phase change………...32
3.3. Correction for motion related artifacts using NWS MRS.….…35
3.4. The procedures of constructive averaging…………………….37
3.4.1. Estimation of phase and frequency shift: matrix-pencil method (MPM) …………………………………………………………….....37
3.4.2 Phase and frequency correction for separate spectra: Klose’s method ………………………………………………………..……...38
3.4.3 Constructive averaging……………………………………….……....38
3.4.4 Summary………………………………………………………...…...38
3.5 Experiments……………….…………………………….….….40
3.6 Results………………………………………………………….44
3.7 Discussion………………………………………...……………45
Chapter 4 Filter diagonalization method (FDM) for quantitative MR spectroscopy……………………………………….……...….46
4.1 Introduction….……………………………………………...….46
4.2. Theory of FDM……………………………………………..…48
4.3 Improvements for FDM……………………………….……….51
4.4 Simulation……………………………………..……….…..…..55
4.4.1 Comparison of FDM with LPSVD and MPM ………….…….....…..55
4.4.2 Different levels of baseline distortion………………….………...…..58
4.4.3 Different levels of water suppression………………….………....…..59
4.4.4 The property of short acquisition time………………….………..…..60
4.5 Phantom study………………………………………………….65
4.6 In vivo spectrum………………………………………………..66
4.7 Using NWS-MRS and FDM for lineshape correction………....67
4.7.1. The effects of macroscopic field inhomogeneity on MRS line-shape distortion………………………………………………………….…..68
4.7.2 Correction methods for field inhomogeneity in MRS……………..…71
4.7.3 Reference deconvolution by FDM (in Time Domain) …………....…72
4.7.4 In vivo experiment……………………………………………………73
4.7.5 Results and discussion………………………..………………………75
Chapter 5 Conclusion………………………………………………….76
References…………………………………………………………..…..7
