Variability of 4D flow parameters when subjected to changes in MRI acquisition parameters using a realistic thoracic aortic phantom

Montalba, Cristián; Urbina, Jesus; Sotelo, Julio; Andía, Marcelo E.; Tejos, Cristián; Irarrázaval, Pablo; Hurtado, Daniel E.; Valverde, Israel; Uribe, Sergio

doi:10.1002/mrm.26834

Cited by 28 publications

(29 citation statements)

References 53 publications

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“…It is well-known that the spatial resolution of MRV is not sufficient to accurately determine the wall shear stress directly from the near-wall velocity gradient. However, it is in general not assumed that a low temporal resolution can reduce the wall shear stress estimation in the same order as the spatial resolution does (Montalba et al 2018;Zimmermann et al 2018). With the use of the temporally highresolved LDV and CFD data of this work, it was shown that the underprediction may indeed be very large.…”

Section: Resultsmentioning

confidence: 99%

Analysis of the wall shear stress in a generic aneurysm under pulsating and transitional flow conditions

et al. 2020

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In this study, the flow through a generic abdominal aneurysm under realistic pulsating flow conditions is examined with magnetic resonance velocimetry (MRV), laser Doppler velocimetry (LDV) and computational fluid dynamics (CFD). The influence of flow phenomena on the wall shear stress (WSS) is examined. It is seen that a strong vortex ring develops during systole at the proximal end of the aneurysm and subsequently travels downstream and decays. The vortex formation plays a major role in the temporal and spatial distribution of the WSS, which is analyzed in detail. A peak of the WSS is observed for a very limited time and in a very localized region where the vortex ring initially develops. The intrinsic temporal averaging during the acquisition of the MRV data is found to significantly decrease this peak. CFD and LDV results, which are averaged in the same manner, show a similar behavior. This indicates that besides the spatial resolution, the temporal resolution is a crucial factor, which needs to be considered especially in flows where vortex rings are observed. Results from LDV and CFD show excellent agreement for the velocity field obtained by MRV. While the flow is found to be laminar in the undilated diameter, results show laminar-turbulent transitional behavior for specific phases of the cycle within the aneurysm bulk. Although MRV is not capable of measuring instantaneous velocity fluctuations, we show that the periodic increase in turbulence intensity can be observed from image artifacts in the MRV data. These artifacts increase the velocity uncertainty, which correlates well with the velocity fluctuations measured with LDV. Although the flow encounters laminar and transitional conditions as well as multiple vortices and stagnation and reattachment points, the improved instabilitysensitive Reynolds stress model, which is used for the numerical simulations of this work, shows very good agreement with the measurements. Significant effort has been expended by numerous research groups in recent years in improving the estimation of WSS from MRV data. However, an assessment of these various post-processing methods is only possible if the true values of the WSS are known. The present study is therefore aimed at providing such ground truth WSS values as well as the corresponding MRV data, allowing also other research groups to validate their WSS estimation methods using the experimental data set presented in this work.

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Section: Resultsmentioning

confidence: 99%

Analysis of the wall shear stress in a generic aneurysm under pulsating and transitional flow conditions

et al. 2020

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“…The hose was connected to a MRI-compatible flow pump (CardioFlow 5000 MR, Shelley Medical Imaging Technologies, London, ON, Canada) with a constant flow rate of 200 mL/s. The system was filled with a blood-mimicking fluid (40% distilled H2O, 60% Glycerol) and the set up was similar as in [12], [13]. The MRI data sets were acquired on a clinical 1.5T Philips Achieva scanner (Philips, Best, The Netherlands).…”

Section: B Phantom Datamentioning

confidence: 99%

Optimal Dual-VENC Unwrapping in Phase-Contrast MRI

Carrillo

Osses

Uribe

et al. 2019

IEEE Trans. Med. Imaging

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Dual-VENC strategies have been proposed to improve the velocity-to-noise ratio in Phase-Contrast MRI. However, they are based on aliasing-free high-VENC data. The aim of this work is hence to propose a dual-VENC velocity estimation method allowing high-VENC aliased data. For this purpose, we reformulate the phase-contrast velocity as a least squares estimator, providing a natural framework for including multiple encoding gradient measurements. By analyzing the mathematical properties of both single-and dual-VENC problems, we can justify theoretically high/low-VENC ratios such that the aliasing velocity can be minimized. The resulting reconstruction algorithm was assessed using three types of data: numerical, experimental and volunteers. In clinical practice, this method would allow shorter examination times by avoiding tedious adaptation of VENC values by repeated scans.

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“…However, 2DRF pulse durations of about 3.5 ms reduced the temporal resolution compared with conventional 1‐dimensional (1D) slab‐selective RF pulses (1DRF, such as SINC) . The temporal resolution is, however, critical for correct peak flow quantification . Furthermore, the reduced FOV (rFOV) needs to be oversampled in both phase‐encoding directions (i.e., rFOV > FOX), to prevent static spatial aliasing, which prolongs the scan time.…”

Section: Introductionmentioning

confidence: 99%

“…15 The temporal resolution is, however, critical for correct peak flow quantification. [16][17][18] Furthermore, the reduced FOV (rFOV) needs to be oversampled in both phase-encoding directions 19 (i.e., rFOV > FOX), to prevent static spatial aliasing, 19 which prolongs the scan time.…”

Section: Introductionmentioning

confidence: 99%

“…Because 4D flow MRI is commonly acquired with n l ≥ 2 to shorten scan durations, UNFOLD may be readily applied. The combination is expected to (1) accelerate 1DRF 4D flow by reducing the FOV, (2) regain the temporal resolution of a respective 1DRF acquisition with n l = 2 by applying UNFOLD to assure peak flow quantification, and (3) diminish dynamic and static aliasing by combining 2DRF and UNFOLD.…”

Section: Introductionmentioning

confidence: 99%

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4D flow imaging with UNFOLD in a reduced FOV

Wink

Bassenge

Ferrazzi

et al. 2019

Magnetic Resonance in Med

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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, nl ≥ 2, are commonly applied in 4D flow MRI to shorten the inherent long scan times. We demonstrate that 2DRF 4D flow with nl ≥ 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 nl = 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 Δteff = 40.5 ms to enhance peak flow quantification.

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Variability of 4D flow parameters when subjected to changes in MRI acquisition parameters using a realistic thoracic aortic phantom

Cited by 28 publications

References 53 publications

Analysis of the wall shear stress in a generic aneurysm under pulsating and transitional flow conditions

Analysis of the wall shear stress in a generic aneurysm under pulsating and transitional flow conditions

Optimal Dual-VENC Unwrapping in Phase-Contrast MRI

4D flow imaging with UNFOLD in a reduced FOV

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