In vivo demonstration of whole-brain multislice multispoke parallel transmit radiofrequency pulse design in the small and large flip angle regimes at 7 Tesla
In vivo demonstration of whole-brain multislice multispoke parallel transmit radiofrequency pulse design in the small and large flip angle regimes at 7 Tesla
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DOI：
10.1002/mrm.26491
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发表时间：
2017-09-01
影响因子：
3.3
通讯作者：
Boulant, Nicolas
中科院分区：
文献类型：
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作者：
Gras, Vincent;Vignaud, Alexandre;Boulant, Nicolas
目的提出一种多脉冲比吸收率（SAR）感知脉冲设计方法，用于均匀多片小和大翻转角（FA）激励并行传输。该方法的目的是在切片特定的方式优化的辐条的位置和射频pulses.MethodsThe问题是作为一组切片特定的幅度最小二乘问题，连接在一起的硬件和SAR的限制，并共同使用一个有效集算法解决。平均哈密顿理论被利用在大FA的情况下，大大减少了计算负担。该方法的数值验证通过模拟和实验两名志愿者在7特斯拉通过应用高分辨率的T2* 加权脑成像protocol.ResultsThe优化高达1300变量下745明确的约束条件可以在小于1和4分钟的小和大FA的情况下，分别进行。联合设计证明了SAR需求协议的价值。与传统的圆偏振模式相比，设计的脉冲增加了超过40%的信号中的70%的voxel.ConclusionThe B1+的不均匀性问题，有效地减轻了在一个多切片近全脑覆盖协议中的小和大FA制度，使用快速切片特定的脉冲设计算法，脉冲进行了优化联合。Magn Reson Med 78：1009-1019，2017年。(c)2016年国际医学磁共振学会。
PurposeA multispoke specific absorption rate (SAR) -aware pulse design approach for homogeneous multiple-slice small and large flip angle (FA) excitations with parallel transmission is proposed. The approach aims at optimizing in a slice-specific manner the spokes locations and radiofrequency pulses.MethodsThe problem is posed as a set of slice-specific magnitude-least-squares problems, linked together by hardware and SAR constraints, and solved jointly using an active-set algorithm. Average Hamiltonian theory is exploited in the large FA case to greatly reduce the computational burden. The approach is validated numerically by means of simulations and experimentally on two volunteers at 7 Tesla through application of a high-resolution T2*-weighted brain imaging protocol.ResultsThe optimization of up to 1300 variables under 745 explicit constraints could be performed in less than 1 and 4min for the small and large FA cases, respectively. The joint design proves valuable for SAR demanding protocols. Compared with the conventional circularly polarized mode, the designed pulses increased the signal by more than 40% in 70% of the voxels.ConclusionThe B1+ inhomogeneity problem was mitigated efficiently in a multislice near whole-brain coverage protocol in the small and large FA regimes using a rapid slice-specific pulse design algorithm where the pulses were optimized jointly. Magn Reson Med 78:1009-1019, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine.