臺灣博碩士論文加值系統

磁振造影中不均勻的脂肪抑制可能導致疑似病變的錯誤判讀。在極度磁場不均勻之情形下，脂肪抑制脈衝甚至會飽和水的訊號而嚴重降低影像品質。目前，已有數種可獲得脂肪抑制的造影方法，如化學選擇脂肪抑制脈衝經常被使用來觀察足踝、關節或頸部之脂肪抑制磁振影像。然而，使用脂肪抑制(快速)自旋回訊技術掃描足踝、關節或頸部時，想要獲得均勻的脂肪抑制是很困難的，這是由於B0和B1磁場不均勻存在所造成的結果。隨著磁場強度增加，遠離中心(off-isocenter)影像及造影部位幾何形狀如頸部及足踝所造成的感磁效應變差都會使脂肪抑制效果降低。可靠、均勻的脂肪抑制在磁振造影中是相當重要的。目前，大部分的方法均會遭遇到次最佳化的訊噪比或是無法得到一致的脂肪抑制等問題。不對稱回訊脂肪和水的重複分解與最小平方評估法(IDEAL)為最新且最有效的脂肪抑制方法。本研究之目的在於使用4種不同的臨床脂肪抑制波序：自旋回訊脂肪抑制、快速自旋回訊脂肪抑制、反轉回復快速自旋回訊及不對稱回訊脂肪和水的重複分解與最小平方評估法波序進行掃描，以評估各種脂肪抑制磁振造影影像是否可獲得可靠的高訊雜比、最佳脂肪抑制效果或均勻之水脂分離及其最佳化的掃描參數。本研究針對12位正常志願者之足踝及頸部進行掃描評估，探討當B0和B1不均勻存在時所造成的影響，並比較不對稱回訊脂肪和水的重複分解與最小平方評估法、脂肪抑制反轉回復快速自旋回訊、脂肪抑制快速自旋回訊與脂肪抑制自旋回訊之差別。本研究定性診斷影像品質及脂肪抑制效果，發現不對稱回訊脂肪和水的重複分解與最小平方評估法技術比臨床例行檢查常用之自旋回訊、快速自旋回訊及反轉回復快速自旋回訊更可有效分離水脂，同時亦可均勻抑制脂肪之訊號，所以不對稱回訊脂肪和水的重複分解與最小平方評估法為本研究脂肪抑制方法中最佳的選擇。本研究之完成可望使病患於臨床例行檢查時獲得可靠的高訊雜比及最佳脂肪抑制效果之水脂肪均勻分離之影像。在臨床應用上，可望提高臨床診斷之準確度。

Inhomogeneous fat suppression on magnetic resonance images may lead to erroneous findings that mimic pathology. In cases of extreme field inhomogeneity, fat suppression pulses can even saturate water signal, and severely degrade image quality. Many methods currently exist for obtaining fat-suppressed images. Fast spin-echo imaging with chemically selective fat suppression pulses is commonly used in ankle, joint and neck MRI for fat suppression. However, achieving uniform fat suppression in the ankle, joint and neck with fat-suppressed fast spin-echo methods is difficult. This is a consequence of the presence of Bo and B1 inhomogeneities, both of which worsen with increasing field strength, off-isocenter imaging, and the unfavorable geometry of the ankle and foot that worsens susceptibility effects. Reliable, uniform fat suppression is important. Multiple approaches currently exist, many of which suffer from either suboptimal signal-to-noise ratio (SNR), or the inability to obtain consistent fat suppression. Echo asymmetry and the least-squares estimation (IDEAL) method is the most recent and effective method for fat suppression. The purpose of this study is to use 4 different clinical pulse sequences, (SE FAT SAT﹐Fast SE FAT SAT﹐FSE STIR and IDEAL) to perform scans. Those data will be used to evaluate whether the various fat suppressed MR images can achieve reliable high signal to noise ratio (SNR), effective optimal fat suppression or homogeneous fat-water separation and their optimal scan parameters. Ankles and necks of twelve normal volunteers were used to perform FAT SAT scanning and evaluation in this study. The influence of B0 and B1 inhomogeneities will be investigated and the differences between IDEAL, inversion recovery fast spin echo and FAT SAT fast spin echo and FAT SAT spin echo had been compared. Qualitative diagnosis of image quality and fat-suppression effects had been studied. It is found that IDEAL technique is obviously superior to clinical routine SE FAT SAT, Fast SE FAT SAT and FSE STIR in both effectiveness of fat-water separation and effect of homogeneous fat suppression. It is expected to provide reliable high SNR and optimal fat suppression efficiency or homogeneous fat–water separation of MR images for patients after the completion of this study. In clinical applications, it is expected to increase the accuracy for clinical diagnosis.

中文摘要i
英文摘要iii
致謝v
目錄vi
圖目錄viii
表目錄xi
第一章 緒論1
1-1 前言1
1-2 研究目的2
1-3 論文架構3
第二章 研究背景與原理4
2-1 研究背景4
2-2 文獻回顧8
2-3 磁振造影的沿革與原理16
2-4 脂肪抑制的原理20
第三章 實驗方法33
3-1 實驗構想33
3-2 實驗材料與設備33
3-3 實驗方法36
第四章 結果43
第五章 討論與結論57
5-1 討論57
5-2 結論58
參考文獻59
圖目錄
圖2-1 足踝關節5
圖2-2 頸部矢狀面解剖圖6
圖2-3 頸椎矢狀面解剖圖7
圖2-4 外加磁場中的質子16
圖2-5 給予射頻後磁向量之變化17
圖2-6 磁向量之回復與衰減18
圖2-7 脂肪頻率選擇飽和法示意圖22
圖2-8 頻率選擇飽和法波序圖23
圖2-9 反轉回復脂肪抑制波序圖25
圖2-10 不同的TE會使脂肪和水同相位或反相位27
圖2-11 兩點式狄克森法波序圖29
圖2-12 水與脂肪隨時間變化之相位圖30
圖3-1 GE 1.5T磁振造影掃描儀34
圖3-2 神經血管陣列線圈34
圖3-3 膝線圈35
圖3-4 正常志願者接受磁振造影掃描頸部之準備及定位36
圖3-5 輸入掃描參數之介面37
圖4-1-1 T2加權脂肪抑制自旋回訊之頸部MR影像45
圖4-1-2 T2加權脂肪抑制快速自旋回訊之頸部MR影像46
圖4-1-3 T2加權反轉回復快速自旋回訊之頸部MR影像46
圖4-2-1 T1加權不對稱回訊脂肪和水的重複分解與最小平方評估法之頸部水脂分離MR影像47
圖4-2-2 T1加權不對稱回訊脂肪和水的重複分解與最小平方評估法之頸部水脂混合MR影像48
圖4-2-3 T2加權不對稱回訊脂肪和水的重複分解與最小平方評估法之頸部水脂分離MR影像49
圖4-2-4 T2加權不對稱回訊脂肪和水的重複分解與最小平方評估法之頸部水脂混合MR影像50
圖4-3-1 T2加權脂肪抑制自旋回訊之足踝脂肪抑制MR影像51
圖4-3-2 T2加權脂肪抑制快速自旋回訊之足踝MR影像51
圖4-3-3 T2加權反轉回復快速自旋回訊之足踝MR影像52
圖4-4-1 T1加權不對稱回訊脂肪和水的重複分解與最小平方評估法之足 踝水脂分離MR影像53
圖4-4-2 T1加權不對稱回訊脂肪和水的重複分解與最小平方評估法之足踝水脂混合MR影像54
圖4-4-3 T2加權不對稱回訊脂肪和水的重複分解與最小平方評估法之足踝水脂分離MR影像55
圖4-4-4 T2加權不對稱回訊脂肪和水的重複分解與最小平方評估法之足踝水脂混合MR影像56
表目錄
表3-1 T2加權脂肪抑制自旋回訊波序之最佳化掃描參數38
表3-2 T2加權脂肪抑制快速自旋回訊波序之最佳化掃描參數39
表3-3 轉回復快速自旋回訊波序之最佳化掃描參數40
表3-4 T1加權不對稱回訊脂肪和水的重複分解與最小平方評估法波序之最佳化掃描參數41
表3-5 T2加權不對稱回訊脂肪和水的重複分解與最小平方評估法波序之最佳化掃描參數42

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