Boulant N, Mangin J-F, Amadon A
CEA, DSV, I2BM, NeuroSpin, LRMN, Gif sur Yvette, France.
Magn Reson Med. 2009 May;61(5):1165-72. doi: 10.1002/mrm.21955.
We report flip angle and spoiled gradient echo measurements at 7 Tesla on human brains in three-dimensional imaging, using strongly modulating pulses to counteract the transmitted radiofrequency inhomogeneity problem. Compared with the standard square pulse results, three points of improvement are demonstrated, namely: (i) the removal of the bright center (typical at high fields when using a quadrature head coil), (ii) the substantial gain of signal in the regions of low B(1) intensity, and (iii) an increased 35% signal uniformity over the whole brain at the flip angle where maximum contrast between white and gray matter occurs. We also find by means of simulations that standard BIR-4 adiabatic pulses need several times more energy to reach a similar performance at the same field strength.
我们报告了在7特斯拉磁场下对人脑进行三维成像时的翻转角和扰相梯度回波测量，使用强调制脉冲来抵消发射射频不均匀性问题。与标准方波脉冲结果相比，展示了三点改进，即：（i）消除了明亮中心（在使用正交头线圈时在高场中典型），（ii）在低B(1)强度区域信号大幅增加，以及（iii）在白质和灰质之间对比度最大的翻转角处，全脑信号均匀性提高了35%。我们还通过模拟发现，标准的BIR-4绝热脉冲在相同场强下需要几倍的能量才能达到类似的性能。
