Untenberger Markus, Tan Zhengguo, Voit Dirk, Joseph Arun A, Roeloffs Volkert, Merboldt K Dietmar, Schätz Sebastian, Frahm Jens
Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
DZHK, German Center for Cardiovascular Research, partner site Göttingen, Germany.
Magn Reson Med. 2016 May;75(5):1901-8. doi: 10.1002/mrm.25696. Epub 2015 Jun 22.
To provide multidimensional velocity compensation for real-time phase-contrast flow MRI.
The proposed method introduces asymmetric gradient echoes for highly undersampled radial FLASH MRI with phase-sensitive image reconstruction by regularized nonlinear inversion (NLINV). Using an adapted gradient delay correction the resulting image quality was analyzed by simulations and experimentally validated at 3 Tesla. For real-time flow MRI the reduced gradient-echo timing allowed for the incorporation of velocity-compensating waveforms for all imaging gradients at even shorter repetition times.
The results reveal a usable degree of 20% asymmetry. Real-time flow MRI with full velocity compensation eliminated signal void in a flow phantom, confirmed flow parameters in healthy subjects and demonstrated signal recovery and phase conservation in a patient with aortic valve insufficiency and stenosis. Exemplary protocols at 1.4-1.5 mm resolution and 6 mm slice thickness achieved total acquisition times of 33.3-35.7 ms for two images (7 spokes each) with and without flow-encoding gradient.
Asymmetric gradient echoes were successfully implemented for highly undersampled radial trajectories. The resulting temporal gain offers full velocity compensation for real-time phase-contrast flow MRI which minimizes false-positive contributions from complex flow and further enhances the temporal resolution compared with acquisitions with symmetric echoes.
为实时相位对比血流磁共振成像提供多维速度补偿。
所提出的方法引入非对称梯度回波用于高度欠采样的径向快速低角度激发磁共振成像，并通过正则化非线性反演（NLINV）进行相位敏感图像重建。使用自适应梯度延迟校正，通过模拟分析所得图像质量，并在3特斯拉下进行实验验证。对于实时血流磁共振成像，减少的梯度回波定时允许在更短的重复时间内为所有成像梯度纳入速度补偿波形。
结果显示20%的非对称度可用。具有完全速度补偿的实时血流磁共振成像消除了流动模型中的信号空洞，确认了健康受试者的血流参数，并在一名主动脉瓣关闭不全和狭窄患者中展示了信号恢复和相位守恒。在1.4 - 1.5毫米分辨率和6毫米切片厚度下的示例性协议，对于有和没有流动编码梯度的两幅图像（各7条辐条），实现了33.3 - 35.7毫秒的总采集时间。
非对称梯度回波已成功应用于高度欠采样的径向轨迹。由此产生的时间增益为实时相位对比血流磁共振成像提供了完全速度补偿，最大限度地减少了复杂血流的假阳性贡献，并与对称回波采集相比进一步提高了时间分辨率。
