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      Quantitative Analysis of Vortical Blood Flow in the Thoracic Aorta Using 4D Phase Contrast MRI

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          Abstract

          Introduction

          Phase contrast MRI allows for the examination of complex hemodynamics in the heart and adjacent great vessels. Vortex flow patterns seem to play an important role in certain vascular pathologies. We propose two- and three-dimensional metrics for the objective quantification of aortic vortex blood flow in 4D phase contrast MRI.

          Materials and Methods

          For two-dimensional vorticity assessment, a standardized set of 6 regions-of-interest (ROIs) was defined throughout the course of the aorta. For each ROI, a heatmap of time-resolved vorticity values

          was computed. Evolution of minimum, maximum, and average values as well as opposing rotational flow components were analyzed. For three-dimensional analysis, vortex core detection was implemented combining the predictor-corrector method with λ 2 correction. Strength, elongation, and radial expansion of the detected vortex core were recorded over time. All methods were applied to 4D flow MRI datasets of 9 healthy subjects, 2 patients with mildly dilated aorta, and 1 patient with aortic aneurysm.

          Results

          Vorticity quantification in the 6 standardized ROIs enabled the description of physiological vortex flow in the healthy aorta. Helical flow developed early in the ascending aorta (absolute vorticity = 166.4±86.4 s -1 at 12% of cardiac cycle) followed by maximum values in mid-systole in the aortic arch (240.1±45.2 s -1 at 16%). Strength, elongation, and radial expansion of 3D vortex cores escalated in early systole, reaching a peak in mid systole (strength = 241.2±30.7 s -1 at 17%, elongation = 65.1±34.6 mm at 18%, expansion = 80.1±48.8 mm 2 at 20%), before all three parameters similarly decreased to overall low values in diastole. Flow patterns were considerably altered in patient data: Vortex flow developed late in mid/end-systole close to the aortic bulb and no physiological helix was found in the aortic arch.

          Conclusions

          We have introduced objective measures for quantification of vortical flow in 4D phase contrast MRI. Vortex blood flow in the thoracic aorta could be consistently described in all healthy volunteers. In patient data, pathologically altered vortex flow was observed.

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          Most cited references 24

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          2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM Guidelines for the diagnosis and management of patients with thoracic aortic disease. A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, American Association for Thoracic Surgery, American College of Radiology,American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons,and Society for Vascular Medicine.

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            Aortic dilation in bicuspid aortic valve disease: flow pattern is a major contributor and differs with valve fusion type.

            Ascending aortic dilation is important in bicuspid aortic valve (BAV) disease, with increased risk of aortic dissection. We used cardiovascular MR to understand the pathophysiology better by examining the links between 3-dimensional flow abnormalities, aortic function, and aortic dilation. A total of 142 subjects underwent cardiovascular MR (mean age, 40 years; 95 with BAV, 47 healthy volunteers). Patients with BAV had predominantly abnormal right-handed helical flow in the ascending aorta, larger ascending aortas (18.3±3.3 versus 15.2±2.2 mm/m²; P<0.001), and higher rotational (helical) flow (31.7±15.8 versus 2.9±3.9 mm²/s; P<0.001), systolic flow angle (23.1°±12.5° versus 7.0°±4.6°; P<0.001), and systolic wall shear stress (0.85±0.28 versus 0.59±0.17 N/m²; P<0.001) compared with healthy volunteers. BAV with right-handed flow and right-non coronary cusp fusion (n=31) showed more severe flow abnormalities (rotational flow, 38.5±16.5 versus 27.8±12.4 mm²/s; P<0.001; systolic flow angle, 29.4°±10.9° versus 19.4°±11.4°; P<0.001; in-plane wall shear stress, 0.64±0.23 versus 0.47±0.22 N/m²; P<0.001) and larger aortas (19.5±3.4 versus 17.5±3.1 mm/m²; P<0.05) than right-left cusp fusion (n=55). Patients with BAV with normal flow patterns had similar aortic dimensions and wall shear stress to healthy volunteers and younger patients with BAV showed abnormal flow patterns but no aortic dilation, both further supporting the importance of flow pattern in the pathogenesis of aortic dilation. Aortic function measures (distensibility, aortic strain, and pulse wave velocity) were similar across all groups. Flow abnormalities may be a major contributor to aortic dilation in BAV. Fusion type affects the severity of flow abnormalities and may allow better risk prediction and selection of patients for earlier surgical intervention.
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              Bicuspid aortic valve: four-dimensional MR evaluation of ascending aortic systolic flow patterns.

              To use time-resolved three-dimensional phase-contrast magnetic resonance (MR) imaging, also called four-dimensional flow MR imaging, to evaluate systolic blood flow patterns in the ascending aorta that may predispose patients with a bicuspid aortic valve (BAV) to aneurysm. The HIPAA-compliant protocol received institutional review board approval, and informed consent was obtained. Four-dimensional flow MR imaging was used to assess blood flow in the thoracic aorta of 53 individuals: 20 patients with a BAV, 25 patients with a tricuspid aortic valve (TAV), and eight healthy volunteers. The Fisher exact test was used to evaluate the significance of flow pattern differences. Nested helical flow was seen at peak systole in the ascending aorta of 15 of 20 patients with a BAV but in none of the healthy volunteers or patients with a TAV. This flow pattern was seen both in patients with a BAV with a dilated ascending aorta (n = 6) and in those with a normal ascending aorta (n = 9), was seen in the absence of aortic stenosis (n = 5), and was associated with eccentric systolic flow jets in all cases. Fusion of right and left leaflets gave rise to right-handed helical flow and right-anterior flow jets (n = 11), whereas right and noncoronary fusion gave rise to left-handed helical flow with left-posterior flow jets (n = 4). Four-dimensional flow MR imaging showed abnormal helical systolic flow in the ascending aorta of patients with a BAV, including those without aneurysm or aortic stenosis. Identification and characterization of eccentric flow jets in these patients may help identify those at risk for development of ascending aortic aneurysm. RSNA, 2010
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                29 September 2015
                2015
                : 10
                : 9
                Affiliations
                [1 ]Department of Radiology and Neuroradiology, University Hospital of Cologne, Cologne, Germany
                [2 ]Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
                COLORADO STATE UNIVERSITY, UNITED STATES
                Author notes

                Competing Interests: The authors have read the journal’s policy and have the following competing interests: Gerard Crelier and Daniel Giese are employees of Gyrotools LLC. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials. All other authors have declared that no competing interests exist.

                Conceived and designed the experiments: JVS GC DG SK DM ACB. Performed the experiments: JVS SK. Analyzed the data: JVS GC DG SK ACB. Contributed reagents/materials/analysis tools: JVS GC SK. Wrote the paper: JVS GC DG SK DM ACB.

                Article
                PONE-D-14-57278
                10.1371/journal.pone.0139025
                4587936
                26418327

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

                Page count
                Figures: 8, Tables: 2, Pages: 19
                Product
                Funding
                The authors have no support or funding to report.
                Categories
                Research Article
                Custom metadata
                All relevant vorticity data are within the paper and its Supporting Information files. Underlying MR datasets are available from the University Hospital of Cologne, Germany, for researchers who meet the criteria for access to confidential data.

                Uncategorized

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