Calculation of Carotid Artery Flow Rates Using Doppler Ultrasound: Implications of Velocity Profile Skewing

2012 ◽  
Author(s):  
Jonathan P. Mynard ◽  
David A. Steinman
Keyword(s):  
Carotid Artery ◽  
Velocity Profile ◽  
Doppler Ultrasound ◽  
Computational Models ◽  
Peak Velocity ◽  
Computational Modelling ◽  
Carotid Bifurcation ◽  
Sample Volume ◽  
Patient Specific ◽  
Specific Flow

Doppler ultrasound (DUS) is a non-invasive means of obtaining patient-specific flow boundary conditions in computational modelling studies [1] or estimating volumetric flow in clinical studies [2, 3]. To convert velocity information to a flow waveform, three related assumptions are often applied, 1) that the peak velocity lies in the centre of a cylindrical vessel, 2) that a centrally-located sample volume will thus detect the peak velocity, and 3) that the velocity profile is fully-developed and axisymmetric, being well-approximated by a parabolic (Poiseuille) or Womersley profile. These assumptions may not always be valid, however, even for nominally straight vessels like the common carotid artery (CCA) [4, 5]. While one might expect that flow estimated from DUS would become increasingly inaccurate as the profile becomes less axisymmetric, the scale of such errors and their relation to the true profile shape have not been quantified for the CCA. Moreover, for a heavily skewed velocity profile, the peak velocity may not lie within the DUS sample volume, and hence the choice of sample volume or beam-vessel orientation may also affect the accuracy of flow calculations. In this study, we investigate these issues by performing an idealized virtual DUS on data from image-based computational models of the carotid bifurcation.

scholarly journals Effect of Inlet Velocity Profiles on Patient-Specific Computational Fluid Dynamics Simulations of the Carotid Bifurcation

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Ian C. Campbell ◽  
Jared Ries ◽  
Saurabh S. Dhawan ◽  
Arshed A. Quyyumi ◽  
W. Robert Taylor ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Velocity Profile ◽  
Carotid Bifurcation ◽  
Velocity Profiles ◽  
Patient Specific ◽  
Flow Waveform ◽  
Specific Flow ◽  
Inlet Velocity ◽  
The Mean

Patient-specific computational fluid dynamics (CFD) is a powerful tool for researching the role of blood flow in disease processes. Modern clinical imaging technology such as MRI and CT can provide high resolution information about vessel geometry, but in many situations, patient-specific inlet velocity information is not available. In these situations, a simplified velocity profile must be selected. We studied how idealized inlet velocity profiles (blunt, parabolic, and Womersley flow) affect patient-specific CFD results when compared to simulations employing a “reference standard” of the patient’s own measured velocity profile in the carotid bifurcation. To place the magnitude of these effects in context, we also investigated the effect of geometry and the use of subject-specific flow waveform on the CFD results. We quantified these differences by examining the pointwise percent error of the mean wall shear stress (WSS) and the oscillatory shear index (OSI) and by computing the intra-class correlation coefficient (ICC) between axial profiles of the mean WSS and OSI in the internal carotid artery bulb. The parabolic inlet velocity profile produced the most similar mean WSS and OSI to simulations employing the real patient-specific inlet velocity profile. However, anatomic variation in vessel geometry and the use of a nonpatient-specific flow waveform both affected the WSS and OSI results more than did the choice of inlet velocity profile. Although careful selection of boundary conditions is essential for all CFD analysis, accurate patient-specific geometry reconstruction and measurement of vessel flow rate waveform are more important than the choice of velocity profile. A parabolic velocity profile provided results most similar to the patient-specific velocity profile.

Analysis of Flow Disturbance in a Stenosed Carotid Artery Bifurcation Using Two-Equation Transitional and Turbulence Models

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
F. P. P. Tan ◽  
G. Soloperto ◽  
S. Bashford ◽  
N. B. Wood ◽  
S. Thom ◽  
...  
Keyword(s):  
Shear Stress ◽  
Carotid Artery ◽  
Laminar Flow ◽  
Wall Shear Stress ◽  
Turbulence Models ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Shear Stresses ◽  
Zone Length ◽  
Wall Shear

In this study, newly developed two-equation turbulence models and transitional variants are employed for the prediction of blood flow patterns in a diseased carotid artery where the growth, progression, and structure of the plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, the laminar-turbulent transition in the poststenotic zone can alter the separation zone length, wall shear stress, and pressure distribution over the plaque, with potential implications for stresses within the plaque. Following the validation with well established experimental measurements and numerical studies, a magnetic-resonance (MR) image-based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using realistic patient-specific conditions. Laminar flow, a correlation-based transitional version of Menter’s hybrid k‐ϵ∕k‐ω shear stress transport (SST) model and its “scale adaptive simulation” (SAS) variant were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress, and turbulence intensity were conducted. In general, the transitional version of SST and its SAS variant are shown to give a better overall agreement than their standard counterparts with experimental data for pulsatile flow in an axisymmetric stenosed tube. For the patient-specific case reported, the wall shear stress analysis showed discernable differences between the laminar flow and SST transitional models but virtually no difference between the SST transitional model and its SAS variant.

Modeling and Realistic Simulation of the Carotid Artery Birfurcation Using 3-D Image Segmentation Implemented in a Commercial Software Package for Hemodynamic Simulation (cvSim™)

2008 ◽  
Author(s):  
Nathan M. Wilson ◽  
Raymond Q. Migrino ◽  
Leanne Harmann ◽  
Robert W. Prost ◽  
John F. LaDisa
Keyword(s):  
Carotid Artery ◽  
Carotid Artery Disease ◽  
3D Structure ◽  
Intima Media Thickness ◽  
Carotid Bifurcation ◽  
The United States ◽  
Time Frame ◽  
Model Construction ◽  
Patient Specific ◽  
Imaging Data

Stroke is the third leading cause of death and a major cause of disability in the United States. Extracranial carotid artery disease is a major risk factor for stroke. Local hemodynamic forces are important in the development and progression of atherogenesis with areas of low and oscillatory wall shear stress (WSS) such as those occurring in the carotid bifurcation being more prone to atheroma development. Despite the importance of WSS in atherosclerosis, there is currently no practical means of measuring this variable clinically. Computational fluid dynamics (CFD) simulations of patient-specific models built from imaging data may provide a clinically relevant solution [1]. For CFD results to be clinically applicable, they need to replicate hemodynamic and imaging measurements to provide physiologic WSS values and the simulation and quantification process must be conducted in a time-frame consistent with the short duration needed for plaque and intima-media thickness assessment. LaDisa, Migrino and colleagues recently reported on a rapid and practical means of generating WSS maps associated with carotid atherosclerosis using patient-specific CFD models derived from 2D and Doppler ultrasound for flow information and MRI for 3D structure before and after 6 months of statin treatment [2]. Although these results were achieved after 17±8 hours/patient instead of days or weeks for prior models, model construction, quantification of results and simulation time were the most time consuming portions of the simulation process with CFD model construction being the most user-intensive portion of the process.

scholarly journals Evaluation of a modified Cheatham-Platinum stent for the treatment of aortic coarctation by finite element modelling

2018 ◽  
Vol 7 ◽  
pp. 204800401877395 ◽  
Author(s):  
Barbara EU Burkhardt ◽  
Nicholas Byrne ◽  
Marí Nieves Velasco Forte ◽  
Francesco Iannaccone ◽  
Matthieu De Beule ◽  
...  
Keyword(s):  
Finite Element ◽  
Aortic Coarctation ◽  
Computational Models ◽  
Three Dimensional ◽  
Computational Modelling ◽  
Patient Specific ◽  
Stent Design ◽  
Initial Length ◽  
Element Analysis

Objectives Stent implantation for the treatment of aortic coarctation has become a standard approach for the management of older children and adults. Criteria for optimal stent design and construction remain undefined. This study used computational modelling to compare the performance of two generations of the Cheatham-Platinum stent (NuMED, Hopkinton, NY, USA) deployed in aortic coarctation using finite element analysis. Design Three-dimensional models of both stents, reverse engineered from microCT scans, were implanted in the aortic model of one representative patient. They were virtually expanded in the vessel with a 16 mm balloon and a pressure of 2 atm. Results The conventional stent foreshortened to 96.5% of its initial length, whereas the new stent to 99.2% of its initial length. Diameters in 15 slices across the conventional stent were 11.6–15 mm (median 14.2 mm) and slightly higher across the new stent: 10.7–15.3 mm (median 14.5 mm) (p= 0.021). Apposition to the vessel wall was similar: conventional stent 31.1% and new stent 28.6% of total stent area. Conclusions The new design Cheatham-Platinum stent showed similar deployment results compared to the conventional design. The new stent design showed slightly higher expansion, using the same delivery balloon. Patient-specific computational models can be used for virtual implantation of new aortic stents and promise to inform subsequent in vivo trials.

Carotid Bifurcation Geometry and Atherosclerosis

Angiology ◽  
2016 ◽  
Vol 68 (9) ◽  
pp. 757-764 ◽  
Author(s):  
Konstantinos Spanos ◽  
Glykeria Petrocheilou ◽  
Christos Karathanos ◽  
Nicos Labropoulos ◽  
Dimitri Mikhailidis ◽  
...  
Keyword(s):  
Carotid Artery ◽  
Computational Models ◽  
Carotid Artery Disease ◽  
Carotid Bifurcation ◽  
External Carotid Artery ◽  
Future Research ◽  
External Carotid ◽  
Potential Marker ◽  
Traditional Risk Factors ◽  
Artery Disease

Hemodynamic changes occurring at the initial segments of the arterial bifurcations appear to play an important role in the development of atherosclerotic plaque. Therefore, arterial geometry might be a potential marker for atherosclerosis. Considerable evidence suggests that geometry can influence local hemodynamics at the carotid bifurcation contributing to the development of atheroma. Bifurcation angle, differences in the area ratios including the flare, proximal curvature, sinus bulb width, and tortuosity of the internal or external carotid artery have been listed as potential contributory elements. These morphometric details have been studied not only in postmortem examination but also with the help of imaging modalities such as ultrasound, digital subtraction angiography, computed tomography angiography, and the assistance of computational models and magnetic resonance angiography. The establishment of certain anatomical and geometrical details in addition to traditional risk factors may help in the identification of patients at high risk of developing carotid artery disease. We reviewed the literature to highlight the evidence on the importance of various geometrical details in the development of carotid atheroma and to suggest areas of future research.

scholarly journals NIMG-65. STUDY OF LOCAL PERTURBATION IN COMPUTATIONAL MODELLING ON TUMOR TREATING FIELDS (TTFIELDS) THERAPY

2020 ◽  
Vol 22 (Supplement_2) ◽  
pp. ii162-ii162
Author(s):  
Oshrit Zeevi ◽  
Zeev Bomzon ◽  
Tal Marciano
Keyword(s):  
Electric Field ◽  
Treatment Planning ◽  
Computational Models ◽  
Computational Modelling ◽  
Clinical Trial Data ◽  
Patient Specific ◽  
Local Perturbation ◽  
Tumor Bed ◽  
Tumor Treating Fields ◽  
Local Perturbations

Abstract INTRODUCTION Tumor Treating Fields (TTFields) are an approved therapy for glioblastoma (GBM). A recent study combining post-hoc analysis of clinical trial data and extensive computational modelling demonstrated that TTFields dose at the tumor has a direct impact on patient survival (Ballo MT, et al. Int J Radiat Oncol Biol Phys, 2019). Hence, there is rationale for developing TTFields treatment planning tools that rely on numerical simulations and patient-specific computational models. To assist in the development of such tools is it important to understand how inaccuracies in the computational models influence the estimation of the TTFields dose delivered to the tumor bed. Here we analyze the effect of local perturbations in patient-specific head models on TTFields dose at the tumor bed. METHODS Finite element models of human heads with tumor were created. To create defects in the models, conductive spheres with varying conductivities and radii were placed into the model’s brains at different distances from the tumor. Virtual transducer arrays were placed on the models, and delivery of TTFields numerically simulated. The error in the electric field induced by the defects as a function of defect conductivity, radius, and distance to tumor was investigated. RESULTS Simulations showed that when a defect of radius R is placed at a distance, d >7R, the error is below 1% regardless of the defect conductivity. Further the defects induced errors in the electric field that were below 1% when σrR/d < 0.16, where σrR/d < 0.16, where σr = (σsphere – σsurrounding)/(σsphere + σsurrounding).σsurroundings is the average conductivity around the sphere and σsphere is the conductivity of the sphere. CONCLUSIONS This study demonstrates the limited impact of local perturbations in the model on the calculated field distribution. These results could be used as guidelines on required model accuracy for TTFields treatment planning.

scholarly journals The Hemodynamic Effect of Enhanced External Counterpulsation Treatment on Atherosclerotic Plaque in the Carotid Artery: A Framework of Patient-Specific Computational Fluid Dynamics Analysis

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Jianhang Du ◽  
Guangyao Wu ◽  
Bokai Wu ◽  
Chang Liu ◽  
Zhouming Mai ◽  
...  
Keyword(s):  
Carotid Artery ◽  
Atherosclerotic Plaque ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Velocity Spectrum ◽  
External Counterpulsation ◽  
Endothelial Surface ◽  
Computational Fluid Dynamics Analysis ◽  
Enhanced External Counterpulsation

Long-term enhanced external counterpulsation (EECP) therapy has been recommended for antiatherogenesis in recent clinical observations and trials. However, the precise mechanism underlying the benefits has not been fully clarified. To quantify the effect of EECP intervention on arterial hemodynamic environment, a framework of numerical assessment was introduced using a parallel computing algorithm. A 3D endothelial surface of the carotid artery with mild atherosclerotic plaque was constructed from images of magnetic resonance angiography (MRA). Physiologic boundary conditions were derived from images of the ultrasound flow velocity spectrum measured at the common carotid artery and before and during EECP intervention. Hemodynamic factors relating to wall shear stress (WSS) and its spatial and temporal fluctuations were calculated and analyzed, which included AWSS, OSI, and AWSSG. Measuring and computational results showed that diastole blood pressure, perfusion, and WSS level in carotid bifurcation were significantly increased during EECP intervention. Mean AWSS level throughout the model increased by 16.9%, while OSI level did not show a significant change during EECP. We thus suggested that long-term EECP treatment might inhibit the initiation and development of atherosclerotic plaque via improving the hemodynamic environment in the carotid artery. Meanwhile, EECP performance induced a 19.6% increase in AWSSG level, and whether it would influence the endothelial functions may need a further study. Moreover, the numerical method proposed in this study was expected to be useful for the instant assessment of clinical application of EECP .

A multi-fidelity modelling approach for evaluation and optimization of wing stroke aerodynamics in flapping flight

2013 ◽  
Vol 721 ◽  
pp. 118-154 ◽  
Author(s):  
Lingxiao Zheng ◽  
Tyson L. Hedrick ◽  
Rajat Mittal
Keyword(s):  
Parameter Space ◽  
Computational Models ◽  
Computational Modelling ◽  
Element Model ◽  
Flapping Wing ◽  
Navier Stokes ◽  
Specific Flow ◽  
Wing Stroke ◽  
Modelling Approach ◽  
Blade Element

AbstractThe aerodynamics of hovering flight in a hawkmoth (Manduca sexta) are examined using a computational modelling approach which combines a low-fidelity blade-element model with a high-fidelity Navier–Stokes-based flow solver. The focus of the study is on understanding the optimality of the hawkmoth-inpired wingstrokes with respect to lift generation and power consumption. The approach employs a tight coupling between the computational models and experiments; the Navier–Stokes model is validated against experiments, and the blade-element model is calibrated with the data from the Navier–Stokes modelling. In the first part of the study, blade-element and Navier–Stokes modelling are used concurrently to assess the predictive capabilities of the blade-element model. Comparisons between the two modelling approaches also shed insights into specific flow features and mechanisms that are lacking in the lower-fidelity model. Subsequently, we use blade-element modelling to explore a large kinematic parameter space of the flapping wing, and Navier–Stokes modelling is used to assess the performance of the wing-stroke identified as optimal by the blade-element parameter survey. This multi-fidelity optimization study indicates that even within a parameter space constrained by the animal’s natural flapping amplitude and frequency, it is relatively easy to synthesize a wing stroke that exceeds the aerodynamic performance of the hawkmoth wing stroke. Within the prescribed constraints, the optimal wing stroke closely approximates the condition of normal hover, and the implications of these findings on hawkmoth flight capabilities as well as on the issue of biomimetic versus bioinspired design of flapping wing micro-aerial vehicles, are discussed.

The Effect of Inlet Flow Profile Simplifications in Computational Fluid Dynamics of the Carotid Bifurcation

2011 ◽  
Author(s):  
Jared Ries ◽  
Ian C. Campbell ◽  
Saurabh S. Dhawan ◽  
Arshed A. Quyyumi ◽  
W. Robert Taylor ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Velocity Profile ◽  
Carotid Bifurcation ◽  
Patient Specific ◽  
Flow Profile ◽  
Inlet Flow ◽  
Measured Velocity ◽  
Inlet Velocity ◽  
Parabolic Flow

Computational fluid dynamics (CFD) is emerging as a powerful tool for researching the role of blood flow in disease processes. Modern clinical imaging technology such as magnetic resonance (MR) angiography and computed tomography (CT) can provide very high resolution information about the geometry of patients’ vasculature for such modeling. However, in many situations, patient-specific inlet velocity information is not available. In these situations, a simplified velocity profile must be selected. In this study, we sought to identify how idealized inlet velocity profiles (blunt flow, parabolic flow, and Womersley flow) affect patient-specific CFD results when compared to simulations employing the real measured velocity profile for each patient. Focusing on the carotid bifurcation, a site prone to atherosclerosis because of its branching geometry and oscillatory flow patterns, we investigated the effect of inlet flow assumptions on hemodynamic parameters known to be associated with atherosclerosis and vascular disease, namely mean wall shear stress (WSS) and oscillatory shear index (OSI) [1].

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