臺灣博碩士論文加值系統

三重磁化準備快速梯度迴訊(MP3RAGE)成像技術在2012年提出，並且實現於1.5T磁場，此技術是在一次激發過程中，收取三組不同反轉時間的影像，修正雙重磁化準備快速梯度迴訊(MP2RAGE)成像技術在測量T1的同時，無法考量反轉隔熱脈衝所帶來的影響。2013年MP3RAGE脈衝序列提出了新的影像合併方法，並推導出其雜訊模型，透過模擬方式找出脈衝序列的最佳反轉時間與其他掃描參數，針對人腦之對比雜訊比(CNR)進行最大化，並且實現於1.5T磁場下。

本研究中，將使用MP3RAGE脈衝序列實現於3T磁場下進行人腦T1之測量，並與IR-FSE、MP2RAGE脈衝序列在相同磁場下進行比較，並且討論IR-FSE、MP3RAGE脈衝序列所使用的反轉隔熱脈衝在人腦中激發效率(Eff)的分布情況。此外，將使用MP3RAGE脈衝序列所提出的影像合併方法與推導的雜訊模型，進行不同切面的CNR最佳化參數計算。

實驗結果得知，IR-FSE、MP2RAGE、MP3RAGE脈衝序列所計算出的T1不盡相同，但皆在T1的合理範圍內。而MP3RAGE脈衝序列在人腦中心處的位置所獲得的Eff皆為1.00、眼球附近約為0.30、鼻竇區域約為0.50~0.70，表示在不同區域位置可能會有不同的激發效率，而MP3RAGE能獲得一組不受激發效率所影響的T1 Mapping；最後CNR最佳化參數實驗結果所量測的組織對比與模擬結果不盡相同，而這是模擬中所假設的T1是根據參考文獻而來，與實際使用MP3RAGE所計算出的T1略有不同，因此若使用本研究中所計算出來的T1搭配實驗掃描參數進行模擬，結果顯示在灰質的訊號與實驗結果相符。

Magnetization Prepared 3 Rapid Gradient Echo (MP3RAGE) was proposed and implemented at 1.5 T in 2012. By receiving three data sets of different inversion times, MP3RAGE achieves T1 mapping without assuming inversion efficiency (Eff) as a global constant in MP2RAGE. Furthermore, the image reconstruction and noise model of MP3RAGE was also derived in 2013, rendering the optimization of contrast-to-noise ratio (CNR) of human brain at 1.5 T.

In this study, the implementation of MP3RAGE pulse sequence at 3T is performed to obtain the whole-brain high resolution T1 mapping. T1 measurement by using IR-FSE and MP2RAGE was compared and the spatial distribution of Eff was discussed. In addition, the CNR optimization has been done by applying the model previously proposed by our team.

The results reveal that the T1 values obtained by IR-FSE, MP2RAGE and MP3RAGE are not identical but still fall in reasonable range according to literatures. Except regions close to the edge of the RF coil or those suffering serious inhomogeneity of susceptibility, most parts of the brain show an Eff of nearly 1.0 in MP3RAGE. In comparison, the value around eyeballs is 0.3 and that of nasal sinus is about 0.50~0.70, which indicates that Eff is location dependent. On the other hand, the in vivo experiment of CNR optimization shows that the tissue contrast of MP3RAGE does not match the simulation very well. This is possibly because the assumption of T1 in simulation differs from with the value measured by the T1 mapping of MP3RAGE. By replacing the T1 relaxation time, it is found that the simulated signal of gray matter agrees with the experimental result perfectly.

審定書 i
致謝 ii
摘要 iii
Abstract iv
目錄 v
表目錄 vii
圖目錄 ix
第一章 簡介 1
第一節 背景 1
第二節 研究動機與目的 4
第二章 脈衝序列 5
第一節 IR-FSE 5
第二節 MP2RAGE 7
第三節 MP3RAGE 10
第四節 CNR定義與最佳化模擬 13
第三章 人體實驗 19
第一節 IR-FSE序列之T1 MAPPING測量 21
第二節 MP2RAGE序列之T1 MAPPING測量 25
第三節 MP3RAGE序列之T1 MAPPING測量 28
第四節 CNR最佳化實驗結果 31
第四章 討論與結論 34
第一節 針對不同序列計算之EFF結果比較 34
第二節 針對不同序列計算之T1 MAPPING結果比較 37
第三節 MP3RAGE脈衝序列的CNR最佳化 41
第四節 結論 46
參考文獻 47

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