PURPOSE: To provide multidimensional velocity compensation for real-time phase-contrast flow MRI. METHODS: 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. RESULTS: 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. CONCLUSION: 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.
PURPOSE: To provide multidimensional velocity compensation for real-time phase-contrast flow MRI. METHODS: 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. RESULTS: 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. CONCLUSION: 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.
Authors: Adam Rich; Michael Gregg; Ning Jin; Yingmin Liu; Lee Potter; Orlando Simonetti; Rizwan Ahmad Journal: Magn Reson Med Date: 2019-11-12 Impact factor: 4.668
Authors: M Markl; S Schnell; C Wu; E Bollache; K Jarvis; A J Barker; J D Robinson; C K Rigsby Journal: Clin Radiol Date: 2016-03-02 Impact factor: 2.350
Authors: Hassan Haji-Valizadeh; Li Feng; Liliana E Ma; Daming Shen; Kai Tobias Block; Joshua D Robinson; Michael Markl; Cynthia K Rigsby; Daniel Kim Journal: NMR Biomed Date: 2020-01-24 Impact factor: 4.044