In vivo three‐dimensional MR wall shear stress estimation in ascending aortic dilatation

Abstract

Purpose To estimate surface-based wall shear stress (WSS) and evaluate flow patterns in ascending aortic dilatation (AscAD) using a high-resolution, time-resolved, three-dimensional (3D), three-directional velocity encoded, radially undersampled phase contrast magnetic resonance sequence (4D PC-MRI). Materials and Methods 4D PC-MRI was performed in 11 patients with AscAD (46.3±22.0 years) and 10 healthy volunteers (32.9±13.4 years) after written informed consent and IRB-approval. Following manual vessel wall segmentation of the ascending aorta (MATLAB, The Mathworks, Natick, MA), a 3D surface was created using spline interpolation. Spatial WSS variation based on surface division in 12 segments and temporal variation were evaluated in AscAD and normal aortas. Visual analysis of flow patterns was performed based on streamlines and particle traces using EnSight (v9.0, CEI, Apex, NC). Results AscAD was associated with significantly increased diastolic WSS, decreased systolic to diastolic WSS ratio, and delayed onset of peak WSS (all P < 0.001). Temporally averaged WSS was increased and peak systolic WSS was decreased. The maximum WSS in AscAD was on the anterior wall of the ascending aorta. Vortical flow with highest velocities along the anterior wall and increased helical flow during diastole were observed in AscAD compared to controls. Conclusion Changes in WSS in the ascending aorta of AscAD correspond to observed alterations in flow patterns compared to controls.

Aortic Valve Stenosis Alters Expression of Regional Aortic Wall Shear Stress: New Insights From a 4‐Dimensional Flow Magnetic Resonance Imaging Study of 571 Subjects

“…Other studies confirm our findings10, 11 and align with the idea that WSS should be reduced in the presence of an enlarged vessel (holding stroke volume constant: mean velocity and thus velocity gradients will be reduced, which, in turn, will reduce WSS) 32. The presence of vortex and supraphysiological helical flow has shown to be significantly increased in the setting of the dilated ascending aorta and an increase in ascending aortic diameter is significantly correlated with the presence of aberrant flow (elevated helix and vortex formation) 33.…”

“…In other patient groups, such as those with trileaflet aortic valves and thoracic aortic dilatation (TAV‐TAA), abnormal blood flow is also known to be present, both with and without AS 10, 11…”

Cardiovascular Magnetic Resonance in Marfan Syndrome

“…CMR is uniquely placed to assess morphology whilst obtaining ecg-gated and spatially-encoded functional information. Therefore attention has now turned to more detailed analysis of aortic flow in MFS by means of 4D (time-resolved 3D) phase-contrast CMR [125][126][127][128]. How this contributes to negative aortic modelling has yet to be elucidated but is the subject of ongoing work [129].…”

Fast and Accurate 4D Flow MRI for Cardiovascular Blood Flow Assessment

“…The increasing number of studies applying the MRI-based WSS estimation in-vivo [23,[34][35][36][37][38][39][40][41][42][43] prompt detailed investigations of the accuracy of MRI-based WSS estimation. Estimates of WSS from 4D flow data in an intracranial aneurysms showed large discrepancies compared to subject-specific CFD simulations [36].…”

“…The use of 4D flow MRI has increased the understanding of normal and abnormal blood flow and has proven valuable in various clinical applications [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Ample evidence indicates that WSS is involved in the pathogenesis of atherosclerosis and aneurysms [28][29][30][31][32][33], and an increasing number of studies apply MRI-based WSS estimation invivo [23,[34][35][36][37][38][39][40][41][42][43]. However, many cardiovascular applications of 4D flow MRI require large volumetric coverage resulting in scan times of about 20-40 minutes, which may be prohibitive in many cases.…”