Accelerated aortic 4D flow MRI with wave-CAIPI

Purpose: The aim of this study was to investigate the acceleration potential of wave-CAIPI (controlled aliasing in parallel imaging) for 4D flow MRI, provided that image quality and precision of flow parameters are maintained. Methods: The 4D flow MRIs with acceleration factor R = 2 were performed on 10 healthy volunteers, using both wave-CAIPI and standard Cartesian/2D-CAIPI sampling for reference. In addition, 1 patient with known aortic valve stenosis was examined. The flow rate (Q), net flow (Q(net)), peak velocity (nu(max)), and net average through-plane velocity ((nu) over bar (perpendicular to)) were calculated in eight analysis planes in the ascending and descending aorta. The acquisitions were retrospectively undersampled (R = 6), and deviations of flow parameters and hemodynamic flow patterns were evaluated. Results: Flow parameters measured with an undersampled wave-CAIPI trajectory showed considerably smaller deviations to the rerferences than the 2D-CAIPI images.For nu(max,) the mean absolute differences were (6.02 +/- 2.08) cm/s versus (14.36 +/- 5.68) cm/s; for Q(net), the mean absolute differences were (3.67 +/- 1.40) nil versus (5.87 +/- 1.91) nil for wave-CAIPI versus 2D-CAIPI, respectively. Noise calculations indicate that the 2D-CAIPI sampling exhibits a (43 +/- 38) % higher average noise level than the wave-CAIPI technique. Qualitative discrepancies in hemodynamic flow patterns, visualized through streamlines, particle traces and flow velocity vectors, could be reduced by using the undersampled wave-CAIPI trajectory. Conclusion: Use of wave-CAIPI instead of 2D-CAIPI sampling in retrospectively 6-fold accelerated 4D flow MRI enhances the precision of flow parameters. The acquisition time of 4D flow measurements could be reduced by a factor of 3, with minimal differences in flow parameters.

Automated summary

This study investigates the acceleration potential of wave-CAIPI for 4D flow MRI, and finds that it enhances the precision of flow parameters while maintaining image quality. Comparison with standard Cartesian/2D-CAIPI sampling shows smaller deviations in flow parameters and reduced qualitative discrepancies in hemodynamic flow patterns when using wave-CAIPI.