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  • Journal article
    Tan FPP, Xu XY, Torii R, Wood NB, Delahunty N, Mullen M, Moat N, Mohiaddin Ret al., 2012,

    Comparison of Aortic Flow Patterns Before and After Transcatheter Aortic Valve Implantation

    , Cardiovascular Engineering and Technology, Vol: 3, Pages: 123-135

    Abstract—Little is known of the likely changes in blood flowvelocity profiles and aortic wall shear stress (WSS) followingtranscatheter aortic valve implantation (TAVI). The objectiveof this study was to investigate the effects of TAVI onflow patterns in the thoracic aorta by using cardiovascularmagnetic resonance imaging (CMR) and computational fluiddynamics (CFD). An elderly patient with aortic stenosis wasexamined using MRI pre- and post-TAVI, and CFDsimulations were carried out incorporating MRI-derivedpatient-specific anatomy and upstream flow conditions. Pre-TAVI velocity profiles demonstrated the highly disturbedturbulent flow and jet impacting the wall of the arch owing tothe partial opening of the stenosed aortic valve, with likelypathological effects. In the Post-TAVI aorta, velocity profileswere similar to those of healthy aortas with spatially moreuniform WSS and lower turbulence levels, demonstrating thefavourable effects of the TAVI procedure in restoring normalaortic flow. This study has shown both the effectiveness ofTAVI on an individual patient and the advantage of thecombined CMR and CFD method for a comprehensivepatient-specific assessment of pre- and post-TAVI aortic flowpatterns and WSS over CMR alone.

  • Journal article
    Zhang X, Luckham PF, Hughes AD, Thom S, Xu XYet al., 2011,

    Development of lysolipid-based thermosensitive liposomes for delivery of high molecular weight proteins

    , INTERNATIONAL JOURNAL OF PHARMACEUTICS, Vol: 421, Pages: 291-292, ISSN: 0378-5173
  • Journal article
    Liu C, Krishnan J, Xu XY, 2011,

    A systems-based mathematical modelling framework for investigating the effect of drugs on solid tumours

    , THEORETICAL BIOLOGY AND MEDICAL MODELLING, Vol: 8, ISSN: 1742-4682
  • Conference paper
    Foin N, Torii R, Mortier P, De Beule M, Viceconte N, Davies JE, Xu XY, Krams R, Di Mario Cet al., 2011,

    Sequential Side Branch and Main Vessel Dilatation instead of Kissing Balloon after Provisional Bifurcation Stenting: Lessons from Micro-CT and Computational Simulations

    , 23rd Annual Transcatheter Cardiovascular Therapeutics (TCT) Symposium, Publisher: ELSEVIER SCIENCE INC, Pages: B82-B82, ISSN: 0735-1097
  • Journal article
    Pierce IT, Gatehouse PD, Xu XY, Firmin DNet al., 2011,

    MR Phase-Contrast Velocity Mapping Methods for Measuring Venous Blood Velocity in the Deep Veins of the Calf

    , JOURNAL OF MAGNETIC RESONANCE IMAGING, Vol: 34, Pages: 634-644, ISSN: 1053-1807
  • Journal article
    Liu C, Krishnan J, Stebbing J, Xu XYet al., 2011,

    Use of mathematical models to understand anticancer drug delivery and its effect on solid tumors

    , PHARMACOGENOMICS, Vol: 12, Pages: 1337-1348, ISSN: 1462-2416
  • Journal article
    Tan FPP, Wood NB, Tabor G, Xu XYet al., 2011,

    Comparison of LES of Steady Transitional Flow in an Idealized Stenosed Axisymmetric Artery Model With a RANS Transitional Model

    , JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 133, ISSN: 0148-0731
  • Journal article
    Starmans-Kool MJ, Stanton AV, Xu YY, Thom SAM, Parker KH, Hughes ADet al., 2011,

    High dietary salt intake increases carotid blood pressure and wave reflection in normotensive healthy young men

    , JOURNAL OF APPLIED PHYSIOLOGY, Vol: 110, Pages: 468-471, ISSN: 8750-7587
  • Journal article
    Ariff BB, Glor FP, Crowe L, Xu XY, Vennart W, Firmin DN, Thom SM, Hughes ADet al., 2010,

    Carotid Artery Hemodynamics: Observing Patient-specific Changes with Amlodipine and Lisinopril by Using MR Imaging Computation Fluid Dynamics

    , RADIOLOGY, Vol: 257, Pages: 662-669, ISSN: 0033-8419
  • Journal article
    Makris GC, Nicolaides AN, Xu XY, Geroulakos Get al., 2010,

    Introduction to the biomechanics of carotid plaque pathogenesis and rupture: review of the clinical evidence

    , BRITISH JOURNAL OF RADIOLOGY, Vol: 83, Pages: 729-735, ISSN: 0007-1285
  • Journal article
    Cheng Z, Tan FPP, Riga CV, Bicknell CD, Hamady MS, Gibbs RGJ, Wood NB, Xu XYet al., 2010,

    Analysis of Flow Patterns in a Patient-Specific Aortic Dissection Model

    , JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 132, ISSN: 0148-0731
  • Conference paper
    Xu Y, McCormack A, Chester A, Hariri B, Sarathchandra P, Rose MLet al., 2010,

    The Indirect Alloimmune Response Causes Endothelial Dysfunction without Endothelial Replacement after Cardiac Transplantation

    , 30th Annual Meeting and Scientific Sessions of the International-Society-for-Heart-and-Lung-Transplantation, Publisher: ELSEVIER SCIENCE INC, Pages: S129-S129, ISSN: 1053-2498
  • 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.

  • 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.

  • 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
    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
    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

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