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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]

Abstract: Hemodynamics has been a very important factor in understanding and diagnosing various vascular diseases. Recently, the X-ray particle image velocimetry (X-ray PIV) method using speckle patterns of blood has been introduced as a new quantitative visualization method for blood flows without any seeding tracer or contrast agents. In this study, the peculiar optical characteristics of blood on the synchrotron X-ray imaging method, which were not presented in previous studies, were investigated in depth and systematically. The experimental conditions required for X-ray PIV application were found to be the distance between the sample and the scintillator (∼40cm), the thickening of the blood sample (>0.3mm), and hematocrit (20.0–80.0%). In addition, we verified that the X-ray PIV method is reliable as an advanced flow velocimetry by comparing the flow rate evaluated from the X-ray PIV result and the input flow rate supplied from a syringe pump with an error of less than 1%. Through this study, based on the understanding of contrast enhancement mechanisms of speckle patterns from blood, we could establish a trustworthy flow visualization method that can be used effectively in hemodynamic studies. [Copyright &y& Elsevier]

Quantifying turbulence velocity fluctuation is important because it indicates the fluid energy dissipation of the blood flow, which is closely related to the pressure drop along the blood vessel. This study aims to evaluate the effects of scan parameters and the target vessel size of 4D phase-contrast (PC)-MRI on quantification of turbulent kinetic energy (TKE). Comprehensive 4D PC-MRI measurements with various velocity-encoding (VENC), echo time (TE), and voxel size values were carried out to estimate TKE distribution in stenotic flow. The total TKE (TKE sum ), maximum TKE (TKE max ), and background noise level (TKE noise ) were compared for each scan parameter. The feasibility of TKE estimation in small vessels was also investigated. Results show that the optimum VENC for stenotic flow with a peak velocity of 125 cm/s was 70 cm/s. Higher VENC values overestimated the TKE sum by up to six-fold due to increased TKE noise , whereas lower VENC values (30 cm/s) underestimated it by 57.1%. TE and voxel size did not significantly influence the TKE sum and TKE noise , although the TKE max significantly increased as the voxel size increased. TKE quantification in small-sized vessels (3–5-mm diameter) was feasible unless high-velocity turbulence caused severe phase dispersion in the reference image. [ABSTRACT FROM AUTHOR]