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Purpose To investigate the details of the flow structure of a plug-like jet that had a vortex ring in pulsatile stenotic phantoms using 4D flow MRI. Method Pulsatile Newtonian flows in two stenotic phantoms with 50% and 75% reductions in area were scanned by 4D flow MRI. Blood analog working fluid was circulated via the stenotic phantom using a pulsatile pump at a constant pulsating frequency of 1 Hz. The velocity and vorticity fields of the plug-like jet with a vortex ring were quantitatively analyzed in the spatial and temporal domains. Results Pulsatile stenotic flow showed a plug-like jet at the specific stenotic degree of 50% in our pulsatile waveform design. This plug-like jet was found at the decelerating period in the post-stenotic region of 26.4 mm (1.2 D). It revealed a vortex ring structure with vorticity strength in the range of ± 100 s − 1 . Conclusion We observed a plug-like jet with a vortex ring in pulsatile stenotic flow by in vitro visualization using 4D flow MRI. In this plug-like jet, the local fastest flow region occurred at the post-systole phase in the post-stenotic region, which was distinguishable from a typical stenotic jet flow at systole phase. [ABSTRACT FROM AUTHOR]

Objectives: To validate 4D flow MRI in a flow phantom using a flowmeter and computational fluid dynamics (CFD) as reference.Methods: Validation of 4D flow MRI was performed using flow phantoms with 75 % and 90 % stenosis. The effect of spatial resolution on flow rate, peak velocity and flow patterns was investigated in coronal and axial scans. The accuracy of flow rate with 4D flow MRI was evaluated using a flowmeter as reference, and the peak velocity and flow patterns obtained were compared with CFD analysis results.Results: 4D flow MRI accurately measured the flow rate in proximal and distal regions of the stenosis (percent error ≤3.6 % in axial scanning with 1.6-mm resolution). The peak velocity of 4D flow MRI was underestimated by more than 22.8 %, especially from the second half of the stenosis. With 1-mm isotropic resolution, the maximum thickness of the recirculating flow region was estimated within a 1-mm difference, but the turbulent velocity fluctuations mostly disappeared in the post-stenotic region.Conclusion: 4D flow MRI accurately measures the flow rates in the proximal and distal regions of a stenosis in axial scan but has limitations in its estimation of peak velocity and turbulent characteristics.Key Points: • 4D flow MRI accurately measures the flow rate in axial scan. • The peak velocity was underestimated by 4D flow MRI. •4D flow MRI demonstrates the principal pattern of post-stenotic flow. [ABSTRACT FROM AUTHOR]