Optimization of RF Excitation to Maximize Signal and T2 Contrast of Tissues With Rapid Transverse Relaxation
Optimization of RF Excitation to Maximize Signal and T2 Contrast of Tissues With Rapid Transverse Relaxation
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DOI：
10.1002/mrm.22433
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发表时间：
2010-08-01
影响因子：
3.3
通讯作者：
Han, Eric
中科院分区：
文献类型：
--
作者：
Carl, Michael;Bydder, Mark;Han, Eric
超短回波时间MRI需要专门的脉冲序列来克服在韧带、肌腱或皮质骨等组织中遇到的MR信号的短T（2）。理论工作，支持的模拟和实验数据优化的射频激励，以最大限度地提高信噪比和对比度噪声比。理论计算和模拟基于经典的Bloch方程，并导致最佳射频脉冲参数的封闭形式的表达式，以最大化在快速T（2）衰减的存在下的MR信号。在稳定状态下，响应于射频激励脉冲的受扰梯度回忆回波信号幅度不是通过经典的恩斯特角而是通过我们称为“广义恩斯特角”的更一般的标准来最大化。“最后，它表明，T（2）的对比度是最大化的翻转与目标T（2）成比例的射频脉冲持续时间在恩斯特角的磁化。对短T（2）体模的实验研究证实了信噪比和对比度噪声比的优化准则。Magn Reson Med 64：481-490，2010. (C)2010 Wiley-Liss，Inc.
Ultrashort echo time MRI requires specialized pulse sequences to overcome the short T(2) of the MR signal encountered in tissues such as ligaments, tendon, or cortical bone. Theoretical work is presented, supported by simulations and experimental data on optimizing the radiofrequency excitation to maximize signal-to-noise ratio and contrast-to-noise ratio. The theoretical calculations and simulations are based on the classic Bloch equations and lead to a closed form expression for the optimal radiofrequency pulse parameters to maximize the MR signal in the presence of rapid T(2) decay. In the steady state, the spoiled gradient recalled echo signal amplitude in response to the radiofrequency excitation pulses is not maximized by the classic Ernst angle but by a more general criterion we call "generalized Ernst angle." Finally, it is shown that T(2) contrast is maximized by flipping the magnetization at the Ernst angle with a radiofrequency pulse duration proportional to the targeted T(2). Experimental studies on short T(2) phantoms confirm these optimization criteria for both signal-to-noise ratio and contrast-to-noise ratio. Magn Reson Med 64:481-490, 2010. (C) 2010 Wiley-Liss, Inc.