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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.
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Markus Untenberger
Zhengguo Tan
Dirk Voit
Magnetic Resonance in Medicine
Max Planck Institute for Biophysical Chemistry
German Centre for Cardiovascular Research
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Untenberger et al. (Mon,) studied this question.
www.synapsesocial.com/papers/69ff603f413f0c047f2d6298 — DOI: https://doi.org/10.1002/mrm.25696