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  • Journal article
    Tan FPP, Torii R, Borghi A, Mohiaddin RH, Wood NB, Xu XYet al., 2009,

    Fluid-structure interaction analysis of wall stress and flow patterns in a thoracic aortic aneurysm

    , International Journal of Applied Mechanics, Vol: 1, Pages: 179-199

    In this study, fluid-structure interaction (FSI) simulation was carried out to predict wall shear stress (WSS) and blood flow patterns in a thoracic aortic aneurysm (TAA) where haemodynamic stresses on the diseased aortic wall are thought to lead to the growth, progression and rupture of the aneurysm. Based on MR images, a patient-specific TAA model was reconstructed. A newly developed two-equation laminar-turbulent transitional model was employed and realistic velocity and pressure waveforms were used as boundary conditions. Analysis of results include turbulence intensity, wall displacement, WSS, wall tensile stress and comparison of velocity profiles between MRI data, rigid and FSI simulations. Velocity profiles demonstrated that the FSI simulation gave better agreement with the MRI data while results for the time-averaged WSS (TAWSS) and oscillatory shear index (OSI) distributions showed no qualitative differences between the simulations. With the FSI model, the maximum TAWSS value was 13% lower, whereas the turbulence intensity was significantly higher than the rigid model. The FSI simulation also provided results for wall mechanical stress in terms of von Mises stress, allowing regions of high wall stress to be identified.
  • Journal article
    Jackson MJ, Wood NB, Zhao S, Augst A, Wolfe JH, Gedroyc WMW, Hughes AD, Thom SA, Xu XYet al., 2009,

    Low wall shear stress predicts subsequent development of wall hypertrophy in lower limb bypass grafts

    , Artery Research, Vol: 3, Pages: 32-38, ISSN: 1872-9312

    Background: Venous grafts commonly develop myointimal hyperplasia, which can lead to stenoses and, ultimately, with expression of adhesion molecules, lumenal occlusion. The aim of the present study was to investigate whether wall shear stress measured post-operatively would predict subsequent myointimal hypertrophy in lower limb venous bypass grafts. Methods: Magnetic resonance imaging and ultrasound were performed in a cohort of patients following lower limb venous bypass graft surgery for peripheral arterial disease at baseline (1e2 weeks) and at follow-up (9e12 months). Wall shear stress was determined at baseline using computational fluid dynamics techniques and intima-media thickness along the length of the graft was measured by ultrasound at baseline and follow up. Results: Complete follow-up was possible in eight patients, in whom low wall shear stress at baseline predicted high intima-media thickness. The relationship between wall shear stress (WSS) and intima-media thickness (IMT)was curvilinear with IMTincreasing sharply at lower levels ofWSS (IMT >1.0 mm at <0.3 Pa). Conclusions: Low wall shear stress is associated with subsequent increase in myointimal thickness in lower limb venous bypass grafts. This is believed to be the first prospective study in humans to demonstrate the relationship between low wall shear stress and myointimal thickening and indicates a likely causative role for lowwall shear stress in the development ofmyointimal hyperplasia.
  • Journal article
    Tan FPP, Soloperto G, Bashford S, Wood NB, Thom S, Hughes A, Xu XYet al., 2008,

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

    , Journal of Biomechanical Engineering, Vol: 130, Pages: 061008-1-061-008-12

    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-/k- 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.
  • Journal article
    Su J, Gu Z, Li Y, Feng S, Xu XYet al., 2008,

    An Adaptive Direct Quadrature Method of Moment for Population Balance Equations

    , AICHE JOURNAL, Vol: 54, Pages: 2872-2887, ISSN: 0001-1541
  • Conference paper
    Torii R, Wood NB, Hadjiloizou N, Dowsey AW, Wright AR, Hughes AD, Davies J, Francis DP, Mayet J, Yang GZ, Thom SAM, Xu XYet al., 2008,

    Differences in coronary artery haemodynamics due to changes in flow and vascular geometry after percutaneous coronary intervention

    , 13th Annual Meeting of the European-Council-for-Cardiovascular-Research, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: 762-762, ISSN: 0194-911X
  • Conference paper
    Torii R, Wood NB, Hadjiloizou N, Dowsey AW, Wright AR, Hughes AD, Davies J, Francis D, Mayet J, Yang GZ, Thom SA, Xu XYet al., 2008,

    Differences in coronary artery haemodynamics due to changes in flow and vascular geometry after percutaneous coronary intervention

    , Annual Scientific Conference of the British-Cardiovascular-Society/British-Society-for-Cardiovascular-Research, Publisher: B M J PUBLISHING GROUP, Pages: A1-A2, ISSN: 1355-6037
  • Journal article
    Long Q, Merrifield R, Xu XY, Kilner P, Firmin DN, Yang G-Zet al., 2008,

    Subject-specific computational simulation of left ventricular flow based on magnetic resonance imaging

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, Vol: 222, Pages: 475-485, ISSN: 0954-4119
  • Journal article
    Downie SP, Raynor SM, Firmin DN, Wood NB, Thom SA, Hughes AD, Parker KH, Wolfe JHN, Xu XYet al., 2008,

    Effects of elastic compression stockings on wall shear stress in deep and superficial veins of the calf

    , AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 294, Pages: H2112-H2120, ISSN: 0363-6135
  • Journal article
    Borghi A, Wood NB, Mohiaddin RH, Xu XYet al., 2008,

    Fluid-solid interaction simulation of flow and stress pattern in thoracoabdominal aneurysms: A patient-specific study

    , JOURNAL OF FLUIDS AND STRUCTURES, Vol: 24, Pages: 270-280, ISSN: 0889-9746
  • Conference paper
    Liu D, Wood NB, Xu XY, Witt N, Hughes AD, Thom SAMet al., 2008,

    3D reconstruction of the retinal arterial tree based on fundus images using a self-calibration approach

    , 1st ECCOMAS Thematic Conference on Computational Vision and Medical Image Processing, Publisher: TAYLOR & FRANCIS LTD, Pages: 307-+
  • Journal article
    Tan FPP, Soloperto G, Wood NB, Thom S, Hughes A, Xu XYet al., 2008,

    Advanced computational models for disturbed and turbulent flow in stenosed human carotid artery bifurcation

    , IFMBE Proceedings, Vol: 21 IFMBE, Pages: 390-394, ISSN: 1680-0737

    In this study, newly developed two-equation transitional and turbulence models are employed for the prediction of blood flow patterns in diseased carotid artery where the growth, progression and structure of plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, laminar-turbulent transition in the post-stenotic zone can alter the separation zone length, wall shear stress and pressure distribution over the plaque, with potential implications for stresses within the plaque. A separate validation study was carried out with well established experimental measurements and numerical studies. Laminar flow, Menter's hybrid k-ε/k-ω Shear Stress Transport model and its transitional version were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress and turbulence intensity were conducted. It was found that the transitional version of SST gave better overall agreement with experimental data for pulsatile flow in an axisymmetric stenosed tube and this is further highlighted in the patient-specific geometry simulation results. A magnetic-resonance (MR) image based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using patient-specific boundary conditions. The laminar flow assumption was found to be inadequate when the differences occurred in the wall shear stress analysis of the patient-derived model. © 2008 Springer-Verlag.
  • Conference paper
    Tan E, Lee S, Torii R, Yang G, Xu X, Wood N, Gedroyc W, Khullar V, Tekkis Pet al., 2008,

    3d modelling of pelvic floor pressures using MRI for evaluating prolapse and obstructed defecation versus asymptomatic controls

    , 38th Annual Meeting of the International-Continence-Society, Publisher: WILEY-BLACKWELL, Pages: 614-615, ISSN: 0733-2467
  • Conference paper
    Tan FPP, Soloperto G, Wood NB, Thom S, Hughes A, Xu XYet al., 2008,

    Advanced Computational Models for Disturbed and Turbulent Flow in Stenosed Human Carotid Artery Bifurcation

    , 4th Kuala Lumpur International Conference on Biomedical Engineering, Publisher: SPRINGER, Pages: 390-+, ISSN: 1680-0737
  • Journal article
    Su J, Gu Z, Li Y, Feng S, Xu XYet al., 2007,

    Solution of population balance equation using quadrature method of moments with an adjustable factor

    , CHEMICAL ENGINEERING SCIENCE, Vol: 62, Pages: 5897-5911, ISSN: 0009-2509
  • Journal article
    Sun N, Wood NB, Hughes AD, Thom SAM, Xu XYet al., 2007,

    Influence of pulsatile flow on LDL transport in the arterial wall

    , ANNALS OF BIOMEDICAL ENGINEERING, Vol: 35, Pages: 1782-1790, ISSN: 0090-6964
  • Journal article
    Augst AD, Ariff B, Thom SAGM, Xu XY, Hughes ADet al., 2007,

    Analysis of complex flow and the relationship between blood pressure, wall shear stress, and intima-media thickness in the human carotid artery

    , AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 293, Pages: H1031-H1037, ISSN: 0363-6135
  • Journal article
    Downie SP, Firmin DN, Wood NB, Thom SA, Hughes AD, Wolfe JNH, Xu XYet al., 2007,

    Role of MRI in investigating the effects of elastic compression stockings on the deformation of the superficial and deep veins in the lower leg

    , JOURNAL OF MAGNETIC RESONANCE IMAGING, Vol: 26, Pages: 80-85, ISSN: 1053-1807
  • Journal article
    Ma CYJ, Kumar R, Xu XY, Mantalaris Aet al., 2007,

    A combined fluid dynamics, mass transport and cell growth model for a three-dimensional perfused biorector for tissue engineering of haematopoietic cells

    , BIOCHEMICAL ENGINEERING JOURNAL, Vol: 35, Pages: 1-11, ISSN: 1369-703X
  • Journal article
    Sun N, Wood NB, Hughes AD, Thom SAM, Xu XYet al., 2007,

    Effects of transmural pressure and wall shear stress on LDL accumulation in the arterial wall: a numerical study using a multilayered model

    , AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 292, Pages: H3148-H3157, ISSN: 0363-6135
  • Conference paper
    Torii R, Wood NB, Hadjiloizou N, Wright A, Hughes AD, Thom SAM, Xu XYet al., 2007,

    Does the difference in realistic waveform before and after stenting affect hemodynamics in stenosed coronary artery?

    , ASME Summer Bioengineering Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 467-468

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