為了改善傳統MPRAGE成像技術在主磁場(B0)強度提升時所伴隨B1磁場不均勻程度增加，雙重磁化準備快速梯度迴訊(MP2RAGE)脈衝序列在2009年被提出。此技術利用一次成像過程中收取兩組不同反轉時間的高解析度原始影像，並經過適當的組合得到一組大幅降低B1不均勻對於影像影響的輸出影像，影像重建的方式分為Ratio與MP2RAGE。

本研究裡，調整對比度定義重現與文獻相符合的3T最佳參數結果，並將調整後的對比度定義根據不同相位編碼方式、不同影像重建技術與不同脈衝序列在1.5T磁場下模擬各自最佳成像參數，最後將模擬結果套入1.5T磁振造影儀進行仿體與人體實驗。由仿體實驗得知SCIC與PURE可以稍微降低影像不均勻性，但效果不顯著，MP2RAGE與Ratio則可大幅改善B1不均勻性。由人體實驗得知MP2RAGE比Ratio更能夠提供較佳影像對比度，中央相位編碼在對比度的表現也優於使用線性相位編碼。

The inhomogeneous B1 field at higher main fields (B0) becomes more serious, leading to unsatisfactory MR image quality. To improve the signal homogeneity of routinely used T1-weighted image, usually acquired by a well-known sequence, Magnetization Prepared Rapid Acquisition Gradient Echo (MPRAGE), a new pulse sequence, Magnetization Prepared 2 Rapid Acquisition Gradient Echoes (MP2RAGE), was proposed in 2009. This technique acquires two sets of high-resolution three- dimentional images at different inversion times after a series of inversion pulses. After any of two simple calculations of the raw images (Ratio or MP2RAGE reconstruction), the output volume was obtained with dramatically reduced spatial inhomogenuity of MR signal.

In this study, the contrast-to-noise ratio (CNR) optimation at 3 T was implemented independently to reproduce the previous results of other group. After that, the simulation of scanning parameters was done to optimize CNR of brain tissue at 1.5 T according to different encoding methods, different pulse sequences, and different reconstruction algorithms. Phantom and human experiments were carried on a 1.5 T scanner for further validation. The results of phantom experiment showed that both MP2RAGE and Ratio reconstructions can achiever better B1 homogeneity than MPRAGE, even with the vendor-equipped correction packages, SCIC and PURE. In addition, the agreement was made between simulation and in-vivo imaging that MP2RAGE provides higher CNR than Ratio when centric encoding also outduels linear encoding.

論文審定書-----i
致謝-----ii
中文摘要-----iii
英文摘要-----iv
圖目錄-----vi
表目錄-----viii
第一章 簡介-----1
第一節 背景-----1
第二節 研究動機與目的-----5
第二章 脈衝序列的分析與比較-----6
第一節 磁化準備快速梯度迴訊(MPRAGE)-----6
第二節 雙重磁化準備快速梯度迴訊：Ratio-----10
第三節 雙重磁化準備快速梯度迴訊：MP2RAGE-----13
第四節 中央相位編碼與線性相位編碼之比較-----15
第三章 模擬-----19
第一節 模擬MPRAGE與MP2RAGE序列之磁振訊號-----19
第二節 CNR最佳化模擬與驗證：3T與7T-----23
第三節 CNR最佳化模擬：1.5T-----34
第四節 模擬討論-----45
第四章 實驗-----52
第一節 實驗設計-----52
第二節 仿體實驗-----53
第三節 人體實驗-----65
第四節 實驗討論-----86
第五章 結論-----89
參考文獻-----93

[1] X. Cui, et al., "Ready...go: Amplitude of the FMRI signal encodes expectation of cue arrival time," PLoS Biol, vol. 7, p. e1000167, Aug 2009.
[2] F. Nelson, et al., "3D MPRAGE improves classification of cortical lesions in multiple sclerosis," Mult Scler, vol. 14, pp. 1214-9, Nov 2008.
[3] J. P. Mugler, 3rd and J. R. Brookeman, "Three-dimensional magnetization-prepared rapid gradient-echo imaging (3D MP RAGE)," Magn Reson Med, vol. 15, pp. 152-7, Jul 1990.
[4] P. J. Wright, et al., "Water proton T1 measurements in brain tissue at 7, 3, and 1.5 T using IR-EPI, IR-TSE, and MPRAGE: results and optimization," MAGMA, vol. 21, pp. 121-30, Mar 2008.
[5] P. A. Bottomley and E. R. Andrew, "RF magnetic field penetration, phase shift and power dissipation in biological tissue: implications for NMR imaging," Phys Med Biol, vol. 23, pp. 630-43, Jul 1978.
[6] C. M. Collins, et al., "Different excitation and reception distributions with a single-loop transmit-receive surface coil near a head-sized spherical phantom at 300 MHz," Magn Reson Med, vol. 47, pp. 1026-8, May 2002.
[7] P. F. Van de Moortele, et al., "B(1) destructive interferences and spatial phase patterns at 7 T with a head transceiver array coil," Magn Reson Med, vol. 54, pp. 1503-18, Dec 2005.
[8] P. F. Van de Moortele, et al., "T1 weighted brain images at 7 Tesla unbiased for Proton Density, T2* contrast and RF coil receive B1 sensitivity with simultaneous vessel visualization," Neuroimage, vol. 46, pp. 432-46, Jun 2009.
[9] M. S. Cohen, et al., "Rapid and effective correction of RF inhomogeneity for high field magnetic resonance imaging," Hum Brain Mapp, vol. 10, pp. 204-11, Aug 2000.
[10] L. Axel, et al., "Intensity correction in surface-coil MR imaging," AJR Am J Roentgenol, vol. 148, pp. 418-20, Feb 1987.
[11] J. Wang, et al., "In vivo method for correcting transmit/receive nonuniformities with phased array coils," Magn Reson Med, vol. 53, pp. 666-74, Mar 2005.
[12] U. Katscher and P. Bornert, "Parallel RF transmission in MRI," NMR Biomed, vol. 19, pp. 393-400, May 2006.
[13] J. P. Marques, et al., "MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at high field," Neuroimage, vol. 49, pp. 1271-81, Jan 15 2010.
[14] R. Deichmann, et al., "Optimization of 3-D MP-RAGE sequences for structural brain imaging," Neuroimage, vol. 12, pp. 112-27, Jul 2000.
[15] A. Tannus and M. Garwood, "Adiabatic pulses," NMR Biomed, vol. 10, pp. 423-34, Dec 1997.
[16] M. A. Bernstein, et al., Handbook of MRI Pulse Sequences: Elsevier Academic Press, 2004.
[17] J. W. Murakami, et al., "Intensity correction of phased-array surface coil images," Magn Reson Med, vol. 35, pp. 585-90, Apr 1996.
[18] R. M. Henkelman, "Measurement of signal intensities in the presence of noise in MR images," Med Phys, vol. 12, pp. 232-3, Mar-Apr 1985.
[19] http://en.wikipedia.org/wiki/Putamen.