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4D flow imaging with UNFOLD in a reduced FOV

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Item Type:Article
Title:4D flow imaging with UNFOLD in a reduced FOV
Creators Name:Wink, C. and Bassenge, J.P. and Ferrazzi, G. and Schaeffter, T. and Schmitter, S.
Abstract:PURPOSE: Two-dimensional selective excitation (2DRF) allows shortening 4D flow scan times by reducing the FOV, but the longer 2DRF pulse duration decreases the temporal resolution, yielding underestimated peak flow values. Multiple k-space lines per cardiac phase, n(l) ≥ 2, are commonly applied in 4D flow MRI to shorten the inherent long scan times. We demonstrate that 2DRF 4D flow with n(l) ≥ 2 can be easily combined with UNFOLD (UNaliasing by Fourier-encoding the Overlaps using the temporaL Dimension), a technique that allows regaining nominally the temporal resolution of the respective acquisition with n(l) = 1, to assure peak flow quantification. METHODS: Two different 2DRF pulses with spiral k-space trajectories were designed and integrated into a 4D flow sequence. Flow phantom experiments and 7 healthy control 4D flow in vivo measurements, with and without UNFOLD reconstructions, were compared with conventional reconstruction and 1D slab-selective excitation (1DRF) by evaluating time-resolved flow curves, peak flow, peak velocity, blood flow volume per cardiac cycle, and spatial aliasing. RESULTS: Applying UNFOLD to 4D flow imaging with 2DRF and reduced FOV increased the quantified in vivo peak flow values significantly by 3.7% ± 2.3% to 5.2% ± 2.4% (P < .05). Accordingly, the peak flow underestimation of 2DRF scans compared with conventional 1DRF scans decreased with UNFOLD. Finally, 2DRF combined with UNFOLD accelerated the 4D flow acquisition 3.5 ± 1.4 fold by reducing the FOV and increasing the effective temporal resolution by 6.7% compared with conventional 1D selective excitation, with 2 k-space lines per cardiac phase. CONCLUSION: Two-dimensional selective excitation combined with UNFOLD allows limiting the FOV to shorten 4D flow scan times and compensates for the loss in temporal resolution with 2DRF (Δt = 64.8 ms) compared with 1DRF (Δt = 43.2 ms), yielding an effective resolution of Δt(eff) = 40.5 ms to enhance peak flow quantification.
Keywords:4D Flow, Fast Imaging, Reduced FOV, Reduced FOX, Spatially Selective 2D RF Excitation, UNFOLD
Source:Magnetic Resonance in Medicine
Page Range:327-338
Date:July 2020
Official Publication:https://doi.org/10.1002/mrm.28120
PubMed:View item in PubMed

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