CEA/DRF/Joliot/NeuroSpin, Université Paris-Saclay, 91191 Gif-sur-Yvette, France.
Siemens Healthcare, 40 avenue des Fruitiers, 93210 Saint-Denis, France.
Magn Reson Imaging. 2019 Sep;61:104-115. doi: 10.1016/j.mri.2019.05.018. Epub 2019 May 17.
To demonstrate that fast-k spokes can be used in parallel transmission to homogenize flip angle ramp profiles (known as TONE) in slab selections, and thereby improve Time-Of-Flight angiography of the whole human brain at 7T.
B and B maps were measured on seven human brains with a z-segmented coil connected to an 8-channel pTx system. Tailored two-spoke pulses were designed under strict hardware and SAR constraints for uniform slab profile before transforming their subpulse waveforms for linearly-increasing flip-angle ramps. Increasing angulations along the feet-head direction were prescribed in 2-slab and 3-slab TOF acquisitions. Excitation patterns were simulated and compared with RF-shimmed (single spoke) ramp pulses. Excitation performances were assessed in ~10-min TOF acquisitions by visually inspecting Maximal Intensity Projections angiograms.
The flip-angle ramp fidelity achieved by double spokes inside slabs of interest was improved by 30-40% compared to RF-shimmed ramps. This allowed better homogenizing signal along arteries, and depicting small vessels in distal areas of the brain, in comparison with RF-shimmed ramp pulses or double-spoke uniform excitation.
Ramp double spokes used in conjunction with parallel transmission yield better blood saturation compensation and more finely resolved TOF angiograms than mere double spokes or ramp single spokes at 7T.
证明在并行传输中可以使用快速-k 桨叶来均匀化切片选择中的翻转角斜坡轮廓（称为 TONE），从而改善 7T 全脑的时间飞跃血管造影。
使用连接到 8 通道 pTx 系统的 z 分段线圈在七个人脑上测量 B 和 B 图。在严格的硬件和 SAR 约束下，为均匀的切片轮廓设计了定制的双桨叶脉冲，并在将其子脉冲波形转换为线性增加的翻转角斜坡之前对其进行变换。在 2 个切片和 3 个切片 TOF 采集过程中，沿着脚到头的方向规定了增加的角度。模拟了激励模式并将其与 RF 调谐（单桨叶）斜坡脉冲进行了比较。通过视觉检查最大强度投影血管造影图来评估约 10 分钟的 TOF 采集中的激励性能。
与 RF 调谐斜坡相比，双桨叶在感兴趣的切片内实现的翻转角斜坡保真度提高了 30-40%。与 RF 调谐斜坡脉冲或双桨叶均匀激励相比，这使得沿动脉的信号均匀化程度更好，并在大脑的远端区域描绘出小血管。
在 7T 下，与仅仅使用双桨叶或斜坡单桨叶相比，与并行传输结合使用的斜坡双桨叶可以提供更好的血液饱和度补偿和更精细的时间飞跃血管造影。
