Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE derived wall shear stiffness of abdominal aorta (original) (raw)
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Estimation of Wall Shear Stress Using 4D Flow Cardiovascular Mri and Computational Fluid Dynamics
Journal of Mechanics in Medicine and Biology, 2017
In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the WSS plays a significant role, together with hemodynamic indicators, in initiation and progression of the vascular diseases. Estimation of WSS values, therefore, may be of clinical significance and the methods employed for its measurement are crucial for clinical community. Recently, four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been widely used in a number of applications for visualization and quantification of blood flow, and although the sensitivity to blood flow measurement has increased, it is not yet able to provide an accurate three-dimensional (3D) WSS distribution. The aim of this work is to evaluate the aortic blood flow features and the associated WSS by the combination of 4D flow cardiovascular magnetic resonance (4D CMR) and computational fluid dynamics technique. In particular, in thi...
Magnetic Resonance in Medicine, 2014
Purpose: To compute cohort-averaged wall shear stress (WSS) maps in the thoracic aorta of patients with aortic dilatation or valvular stenosis and to detect abnormal regional WSS. Methods: Systolic WSS vectors, estimated from fourdimensional flow MRI data, were calculated along the thoracic aorta lumen in 10 controls, 10 patients with dilated aortas, and 10 patients with aortic valve stenosis. Three-dimensional segmentations of each aorta were coregistered by group and used to create a cohort-specific aortic geometry. The WSS vectors of each subject were interpolated onto the corresponding cohort-specific geometry to create cohort-averaged WSS maps. A Wilcoxon rank sum test was used to generate aortic P-value maps (P<0.05) representing regional relative WSS differences between groups. Results: Cohort-averaged systolic WSS maps and P-value maps were successfully created for all cohorts and comparisons. The dilation cohort showed significantly lower WSS on 7% of the ascending aorta surface, whereas the stenosis cohort showed significantly higher WSS on 34% of the ascending aorta surface.
Journal of Cardiovascular Magnetic Resonance, 2014
Actual methods to quantify wall shear stress (WSS) are performed on reformatted 2D planes from 4D flow data sets. This approach has the inherit limitation that only a few planes are analyzed on specific locations of the aorta, even though the full 3D velocity field is usually available. Another problem with this approach is that the process of locating 2D planes manually is dependent on the user and may lead to results that have low reproducibility. These problems can be circumvented by calculating the WSS in 3D directly. A few methods based on computational fluid dynamics (CFD) have been proposed to obtain 3D WSS. These methods use realistic vascular geometries extracted from MR data, however, assumptions are made on the properties of the walls and on flow velocity profiles that may not be fully realistic. In this work, we propose a novel methodology based on finite-element (FE) interpolations to compute the 3D WSS of the whole thoracic aorta from 4D flow MRI data.
IEEE Transactions on Medical Imaging, 2016
Wall shear stress (WSS) and oscillatory shear index (OSI) are important parameters for the assessment of the loss of vascular function and the integrity of the vessel tissue. Several methods have been proposed to estimate WSS and OSI from PC-MRI, where the in-plane gradients of velocity on 2D planes are approximated through finite differences or differentiation of other interpolation schemes. However, such methods neglect the longitudinal velocity gradients that typically arise in cardiovascular flow, particularly on vessel geometries whose cross section and centerline orientation strongly vary in the axial direction. Thus, the contribution of longitudinal velocity gradients to the estimation of WSS and OSI remains understudied. In this work, we propose a 3D finite-element method for the quantification of WSS and OSI from 3D CINE PC-MRI that accounts for both in-plane and longitudinal velocity gradients. We demonstrate the convergence and robustness of the method on cylindrical geometries using a synthetic phantom based on the Poiseuille flow equation. We also show that, in the presence of noise, the method is both stable and accurate for voxel sizes that are in the range of those found in routine medical imaging procedures. Using computational fluid dynamics simulations on curved geometries with rigid walls as a benchmark, we show that the proposed 3D method results in more accurate WSS estimates than those obtained from a 2D analysis not considering out-of-plane velocity gradients,
European Heart Journal – Cardiovascular Imaging, 2016
Introduction: Preoperative diagnostic protocols of abdominal aortic aneurysm (AAA) are today mainly based on the measurement of the aortic maximum diameter. This measurement is insufficient because the diameter is not a discriminant variable for predicting the rupture of the aorta. Recent works show the importance of determining the wall stress both due to the aortic shape, the pressure and the blood flow. The problem is very complex and requires the implementation of sophisticated models taking into account the heterogeneity of tissues and the complexity of flow. Then it is essential to validate the capacity of existing medical imaging systems to provide reliable measurements that will be introduced in these models. Method: The aim of this study is to verify the MRI's ability to provide reliable measurements, firstly for the deformation of the aortic wall, and secondly for the blood flow. Cine MRI acquisitions (SSFP sequence) enabled to accurately determine the geometry and deformation of the aneurysm and 4D flow MRI measurements (thanks to a 3D PC-MRI sequence) were used to quantify the velocities of the fluid. Measurements were carried out in vitro with an experimental device that simulated hemodynamic circulation on a realistic AAA phantoms in silicone that have properties closest as possible as the actual physiological conditions. The sequences were prospectively gated with the pressure signal given by a pressure sensor. The deformations of the phantom wall were then determined through solid modeling with Abaqus software in which the geometry and internal stresses determined by CFD modeling (pressure, Wall Shear Stress) were introduced (see ). The deformations were compared with measurement made by stereovision. Moreover, blood flow estimation with MRI was compared with the fluid modelling performed with ANSYS software.
Characterization of Abnormal Wall Shear Stress Using 4D Flow MRI in Human Bicuspid Aortopathy
Annals of Biomedical Engineering, 2014
There exists considerable controversy surrounding the timing and extent of aortic resection for patients with BAV disease. Since abnormal wall shear stress (WSS) is potentially associated with tissue remodeling in BAV-related aortopathy, we propose a methodology that creates patient-specific 'heat maps' of abnormal WSS, based on 4D flow MRI. The heat maps were created by detecting outlier measurements from a volumetric 3D map of ensemble-averaged WSS in healthy controls. 4D flow MRI was performed in 13 BAV patients, referred for aortic resection and 10 age-matched controls. Systolic WSS was calculated from this data, and an ensembleaverage and standard deviation (SD) WSS map of the controls was created. Regions of the individual WSS maps of the BAV patients that showed a higher WSS than the mean + 1.96SD of the ensemble-average control WSS map were highlighted. Elevated WSS was found on the greater ascending aorta (35% ± 15 of the surface area), which correlated significantly with peak systolic velocity (R 2 = 0.5, p = 0.01) and showed good agreement with the resected aortic regions. This novel approach to characterize regional aortic WSS may allow clinicians to gain unique insights regarding the heterogeneous expression of aortopathy and may be leveraged to guide patient-specific resection strategies for aorta repair.
Journal of Clinical Medicine
Objectives: Four-dimensional (4D) flow cardiac magnetic resonance (CMR) represents an emerging technique for non-invasive evaluation of the aortic flow. The aim of this study was to investigate a 4D-flow CMR sequence for the assessment of thoracic aorta comparing different vendors and different magnetic fields of MR scanner in fifteen healthy volunteers. Methods: CMR was performed on three different MRI scanners: one at 1.5 T and two at 3 T. Flow parameters and planar wall shear stress (WSS) were extracted from six transversal planes along the full thoracic aorta by three operators. Inter-vendor comparability as well as scan–rescan, intra- and interobserver reproducibility were examined. Results: A high heterogeneity was found in the comparisons for each operator and for each scanner in the six transversal planes analysis (Friedman rank-sum test; p-value ≤ 0.05). Among all, the most reproducible measures were extracted for the sinotubular junction plane and for the flow parameters. ...