本研究使用IR-FSE、MP2RAGE與自行開發的MP3RAGE三種不同的磁振脈衝序列在1.5T的磁場下，進行全腦組織高解析度T1 mapping量測。MP2RAGE為三維快速梯度迴訊之序列，使用這個技術可以獲得兩個不同反轉時間的訊號，並根據Bloch equation，可建立收取的磁振訊號與T1弛緩參數之間的關係，進一步推算出每個像素的T1弛緩參數。然而，反轉射頻脈衝的激發效率也會影響收取的訊號大小，在文獻中，前人藉由數值模擬針對所使用的隔熱脈衝計算出激發效率以完成T1 mapping，然而，實際狀況中的脈衝效率在造影範圍內可能並非單一常數，因此在本研究中，一種改良版的脈衝序列MP3RAGE被提出，在不增加掃描時間的前提下，多收取一組不同TI的訊號，並藉由對於非線性方程組求解，分別實際算出T1弛緩參數與脈衝效率。此外，在每次實驗當中也使用IR-FSE技術進行T1弛緩參數的量測做為相同解析度下對照的標準。實驗結果發現，在考慮反轉脈衝效率下，使用IR-FSE序列的量測結果與文獻中報告的數值相當接近。此外，利用MP2RAGE所獲得的T1也在合理的範圍之內，但相較於IR-FSE的結果有偏大的現象，這可能與脈衝效率的假設過高有密切的關係。在使用新的MP3RAGE後，成功的獲得全腦高解析度的T1弛緩參數分佈圖以及相對應的脈衝效率分佈，然而，由於非線性運算較容易受到雜訊的影響，與MP2RAGE的結果比較起來，可發現在相同組織內的量測結果顯得較不均勻，但在對脈衝效率分佈圖進行簡單的平滑化並代回重新計算T1弛緩參數之後，就可獲得更接近於IR-FSE的結果。

In this study, three different MR pulse sequences, IR-FSE, MP2RAGE, and firstly proposed MP3RAGE, were applied to obtain high-resolution 3D T1 mapping of whole brain at 1.5 Tesla. Among these three sequences, MP2RAGE uses fast gradient echo as readout module. Signals of two different inversion times are acquired at once and can be used to calculate T1 relaxation time according to Bloch equation. However, the magnetization was also influenced by the excitation efficiency of inversion adiabatic pulse, which was usually estimated by numerical simulation and taken as a constant over the field of view in the literature. However, this might not be true in practice. Therefore, a newly modified pulse sequence, MP3RAGE, was proposed to acquire data of three distinct inversion times without increasing scanning time. As a result, the spatial distribution of T1 and inversion efficiency can be assessed by solving nonlinear least square problem. In addition, the IR-FSE sequence with six inversion times was also applied in every experiment to provide T1 value for reference. Results showed that the T1 estimation obtained by MP2RAGE is close to, but slightly lower than that by IR-FSE, which is in agreement with those reported in literatures. In addition, the 3D high-resolution maps of T1 and efficiency were successfully estimated with the use of MP3RAGE. Spatial smoothing on inversion efficiency helps reducing the sensitivity to noise in the nonlinear approach, leading to T1 values closer to those by IR-FSE.

論文審定書 i
致謝 ii
中文摘要 iii
英文摘要 iv
目錄 v
表目錄 vii
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 脈衝序列的分析與比較 6
第一節 反轉回復快速自旋迴訊：IR- FSE 6
第二節 雙重磁化準備快速梯度迴訊：MP2RAGE 11
第三節 雙重磁化準備快速梯度迴訊：MP3RAGE 16
第三章 實驗結果 20
第一節 模擬IR-FSE序列之磁振訊號與eff、T1 mapping量測 21
第二節 模擬MP2RAGE序列之磁振訊號與T1 mapping量測 29
第三節 模擬MP3RAGE序列之磁振訊號與eff、T1 mapping量測 39
第四章 結果比較與討論 46
第五章 結論 53
參考文獻 55

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