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  • Journal article
    Torii R, Keegan J, Wood NB, Dowsey AW, Hughes AD, Yang G-Z, Firmin DN, Thom SA, Xu Yet al., 2010,

    MR image-based geometric and hemodynamic investigation of the right coronary artery withdynamic vessel motion

    , Annals of Biomedical Engineering, Vol: in press

    The aim of this study was to develop a fully subject-specific model of the right coronaryartery (RCA), including dynamic vessel motion, for computational analysis to assess the effects ofcardiac-induced motion on hemodynamics and resulting wall shear stress (WSS). Vascular geometrieswere acquired in the right coronary artery (RCA) of a healthy volunteer using a navigator-gatedinterleaved spiral sequence at 14 time points during the cardiac cycle. A high temporal resolutionvelocity waveform was also acquired in the proximal region. Cardiac-induced dynamic vessel motionwas calculated by interpolating the geometries with an active contour model and a CFD simulationwith fully subject-specific information was carried out using this model. The results showed theexpected variation of vessel radius and curvature throughout the cardiac cycle, and also revealed thatdynamic motion of the right coronary artery consequent to cardiac motion had significant effects oninstantaneous WSS and oscillatory shear index (OSI). Subject specific MRI-based CFD is feasible and, ifscan duration could be shortened, this method may have potential as a non-invasive tool to investigatethe physiological and pathological role of hemodynamics in human coronary arteries.

  • Journal article
    Soloperto G, Keenan NG, Sheppard MN, Ohayon J, Wood NB, Pennell DJ, Mohiaddin RH, XY Xet al., 2010,

    Combined imaging, computational and histological analysis of a ruptured carotid plaque: A patient-specific analysis.

    , Artery Research, Vol: 4, Pages: 59-65

    Background: Rupture of carotid plaques is an important cause of cerebrovascularevents. Several factors, including wall shear stress (WSS), plaque morphology and peak capstress, have been associated with plaque vulnerability. The aim of this study was to investigatethe relationship between these factors in an in vivo human ruptured carotid plaque.Methods: A 74-year-old male presenting with a transient ischemic attack underwent carotidmagnetic resonance imaging (MRI), which indicated a ruptured plaque, followed by carotidendarterectomy, from which plaque histology was assessed. The carotid bifurcation was reconstructedfrom the MRI data, and three-dimensional flow simulations were performed usingcomputational fluid dynamics to determine WSS and related parameters. Plaque vulnerabilitywas assessed using a biomechanical method based on modified Glagov criteria.Results: The plaque rupture was just distal to the site of maximum stenosis in a region of lowWSS, where MRI and histology both demonstrated fibrous cap thinning, a large lipid pool andcalcification in the shoulder region. Plaque vulnerability analysis indicated critically vulnerableplaque at the rupture site by a wide margin.Conclusions: Both low and high WSS have been associated with plaque vulnerability, and highmechanical stress in the cap has been linked to plaque rupture, but these parameters are notroutinely assessed clinically. This study demonstrates a complete analysis by combiningimaging, histology and bio-fluid and biomechanical modelling.

  • Conference paper
    Soloperto G, Keenan N, Sheppard M, Wood N, Pennell DJ, Mohiaddin R, Xu XYet al., 2009,

    A COMBINED IMAGING, COMPUTATIONAL AND HISTOLOGICAL ANALYSIS OF A RUPTURED CAROTID ARTERY

    , Spring Meeting of the British-Society-for-Cardiovascular-Research, Publisher: B M J PUBLISHING GROUP, ISSN: 1355-6037
  • Journal article
    Soloperto G, Keenan NG, Chan C, Sheppard MN, Wood NB, Pennell DJ, Mohiaddin RH, Xu XYet al., 2009,

    Comparison between ruptured and intact atherosclerotic plaques: flow- modelling study of in vivo carotid arteries by cardiovascular magnetic resonance

    , EUROPEAN HEART JOURNAL, Vol: 30, Pages: 763-763, ISSN: 0195-668X
  • Journal article
    Su J, Gu Z, Xu XY, 2009,

    Advances in numerical methods for the solution of population balance equations for disperse phase systems

    , SCIENCE IN CHINA SERIES B-CHEMISTRY, Vol: 52, Pages: 1063-1079, ISSN: 1006-9291
  • Journal article
    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., 2009,

    Fluid-structure interaction analysis of a patient-specific right coronary artery with physiological velocity and pressure waveforms

    , Communications in Numerical Methods in Engineering, Vol: 25, Pages: 565-580, ISSN: 1069-8299

    Coupled fluid-structure interaction (FSI) analysis of the human right coronary artery (RCA) has been carried out to investigate the effects of wall compliance on coronary hemodynamics. A 3-D model of a stenosed RCA was reconstructed based oil multislice computerized tomography images. A velocity waveform in the proximal RCA and a pressure waveform in the distal RCA of a patient with a severe stenosis were acquired with a catheter delivered wire probe and applied as boundary conditions. The arterial wall was modeled as a Mooncy-Rivlin hyperelastic material. The predicted maximum wall displacement (3.85 mm) was comparable with the vessel diameter (similar to 4 mm), but the diameter variation was much smaller, 0.134 mm at the stenosis and 0.486 mm in the distal region. Comparison of the computational results between the FSI and rigid-wall models showed that the instantaneous wall shear stress (WSS) distributions were affected by diameter variation in the arterial walk increasing systolic blood pressure dilated the vessel and consequently lowered WSS, whereas the opposite occurred When pressure started to decrease. However. file effects of wall compliance on time-averaged WSS (TAWSS) and oscillatory shear index (OSI) were insignificant (4.5 and 2.7% difference in maximum TAWSS and OSI. respectively). Copyright (C) 2009 John Wiley & Sons, Ltd.

  • Journal article
    Giannakoulas G, Dimopoulos K, Xu XY, 2009,

    Modelling in congenital heart disease. Art or science?

    , INTERNATIONAL JOURNAL OF CARDIOLOGY, Vol: 133, Pages: 141-144, ISSN: 0167-5273
  • Journal article
    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., 2009,

    Stress phase angle depicts differences in coronary artery hemodynamics due to changes in flow and geometry after percutaneous coronary intervention

    , American Journal of Physiology - Heart and Circulatory Physiology, Vol: 296, Pages: H765-H776, ISSN: 0363-6135

    Torii R, Wood NB, Hadjiloizou N, Dowsey AW, Wright AR, Hughes AD, Davies J, Francis DP, Mayet J, Yang G, Thom SA, Xu XY. Stress phase angle depicts differences in coronary artery hemodynamics due to changes in flow and geometry after percutaneous coronary intervention. Am J Physiol Heart Circ Physiol 296: H765-H776, 2009. First published January 16, 2009; doi:10.1152/ajpheart.01166.2007.-The effects of changes in flow velocity waveform and arterial geometry before and after percutaneous coronary intervention (PCI) in the right coronary artery (RCA) were investigated using computational fluid dynamics. An RCA from a patient with a stenosis was reconstructed based on multislice computerized tomography images. A nonstenosed model, simulating the same RCA after PCI, was also constructed. The blood flows in the RCA models were simulated using pulsatile flow waveforms acquired with an intravascular ultrasound-Doppler probe in the RCA of a patient undergoing PCI. It was found that differences in the waveforms before and after PCI did not affect the time-averaged wall shear stress and oscillatory shear index, but the phase angle between pressure and wall shear stress on the endothelium, stress phase angle (SPA), differed markedly. The median SPA was -63.9 degrees (range, -204 degrees to -10.0 degrees) for the pre-PCI state, whereas it was 10.4 degrees (range, -71.1 degrees to 25.4 degrees) in the post-PCI state, i.e., more asynchronous in the pre-PCI state. SPA has been reported to influence the secretion of vasoactive molecules (e. g., nitric oxide, PGI(2), and endothelin-1), and asynchronous SPA (approximate to -180 degrees) is proposed to be proatherogenic. Our results suggest that differences in the pulsatile flow waveform may have an important influence on atherogenesis, although associated with only minor changes in the time-averaged wall shear stress and oscillatory shear index. SPA may be a useful indicator in predicting sites prone to atherosclerosis.

  • Journal article
    Gu Z, Su J, Jiao J, Xu XYet al., 2009,

    Simulation of micro-behaviors including nucleation, growth, and aggregation in particle system

    , SCIENCE IN CHINA SERIES B-CHEMISTRY, Vol: 52, Pages: 241-248, ISSN: 1006-9291
  • Journal article
    Sun N, Torii R, Wood NB, Hughes AD, Thom SAM, Xu XYet al., 2009,

    Computational Modeling of LDL and Albumin Transport in an In Vivo CT Image-Based Human Right Coronary Artery

    , JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 131, ISSN: 0148-0731
  • Conference paper
    Liu D, Wood NB, Xu XY, Witt N, Hughes ADet al., 2009,

    3D Reconstruction of the Retinal Arterial Tree Using Subject-Specific Fundus Images

    , 1st ECCOMAS Thematic Conference on Computational Vision and Medical Image Processing, Publisher: SPRINGER, Pages: 187-+
  • Journal article
    Liu D, Wood NB, Witt N, Hughes AD, Thom SA, Xu XYet al., 2009,

    Computational Analysis of Oxygen Transport in the Retinal Arterial Network

    , CURRENT EYE RESEARCH, Vol: 34, Pages: 945-956, ISSN: 0271-3683
  • Conference paper
    Liu D, Wood NB, Xu XY, Witt N, Hughes AD, Thom SAet al., 2009,

    Image-based Blood Flow Simulation in the Retinal Circulation

    , 4th European Conference of the International Federation for Medical and Biological Engineering (ECIFMBE), Publisher: SPRINGER, Pages: 1963-1966, ISSN: 1680-0737
  • Conference paper
    Soloperto G, Keenan N, Sheppard M, Wood N, Pennell DJ, Mohiaddin R, Xu XYet al., 2009,

    PLAQUE RUPTURE IN THE CAROTID ARTERY: A COMBINED IMAGING, COMPUTATIONAL AND HISTOLOGICAL ANALYSIS

    , ASME Summer Bioengineering Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1075-1076
  • Journal article
    Torii R, Keegan J, Wood NB, Dowsey AW, Hughes AD, Yang G-Z, Firmin DN, Thom SAM, Xu XYet al., 2009,

    The effect of dynamic vessel motion on haemodynamic parameters in the right coronary artery: a combined MR and CFD study

    , BRITISH JOURNAL OF RADIOLOGY, Vol: 82, Pages: S24-S32, ISSN: 0007-1285
  • Journal article
    Sun N, Leung JH, Wood NB, Hughes AD, Thom SA, Cheshire NJ, Xu XYet al., 2009,

    Computational analysis of oxygen transport in a patient-specific model of abdominal aortic aneurysm with intraluminal thrombus

    , BRITISH JOURNAL OF RADIOLOGY, Vol: 82, Pages: S18-S23, ISSN: 0007-1285
  • 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.

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

    Analysis of flow patterns in a patient-specific thoracic aortic aneurysm model

    , Publisher: Elsevier, Pages: 680-690

    In this study, a newly developed two-equation transitional model was employed for the prediction of blood flow patterns in a thoracic aortic aneurysm (TAA) where the growth and progression are closely linked to low and oscillating wall shear stresses. Laminar–turbulent transition in the dilated vessel can alter the flow structure, shear stress and pressure distribution within the aneurysm. A patient-specific TAA model was reconstructed from magnetic-resonance (MR) images and measured velocity waveform was used as the inflow condition. Laminar flow and a correlation-based transitional version of Menter’s hybrid k /k x Shear Stress Transport (SST Tran) model were implemented in pulsatile simulations from which WSS distribution was obtained throughout a cardiac cycle and velocity profiles were compared with MR measurements. The correlation-based transitional model was found to produce results in closer agreement with the MR data than the laminar flow simulation.

  • 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.

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