- Email: [email protected]
Comparison of measured and simulated deformation of a left ventricle
Track 14. Cardiovascular Mechanics
and is shifted for higher values of pressure if the wall thickness is increased. Our results are in agreement with experimental observations. 7027 Th, 08:30-08:45 (P38) Computational simulation of blood flow in the human left ventricle W. Schiller 1, T. Schmid 3, K. Spiegel 2, S. Donisi 2, C. Probst 1, A. Kovacz 4, S. Flacke 4, D. Liepsch 3, H. Oertel 2 . 1KIinik und Poliklinik for Herzchirurgie, Universit#t Bonn, Germany, 21nstitut for Str6mungslehre, Universit#t Karlsruhe, Germany, 3Lehrstuhl for Str6mungsmechanik, Fachhochschule MEtnchen, Germany, 4Radiologische Klinik, Universit#t Bonn, Germany Aim of our project was to simulate intracardiac blood flow in the human left heart to reveal changes in flow patterns and energy losses depending on different pathologies. The presented virtual heart model is based on data from real human hearts. Magnetique Resonance Imaging (MRI) was used to get time-depending geometry and intraventricular flow from healthy and pathological human left ventricles and the adjacent left atrium. After segmentation and post processing of the data, a preformed aorta and heart valves as passive components were inserted and coupled to the model. The numerical flow calculation was performed with a finite volume method. Boundary conditions such as preand afterload were given by a simplified circulation model. An experimental validation comprising flow measurements (LDA- and PIV-measurements) in a silicone ventricle which represents the exact geometry of the virtual ventricle showed high correlation to the computational flow simulation. The comparison of MRI -flow measurements and numerical simulation data revealed the impact of procedural influences such as MRI scanning, segmentation and postprocessing. The developed method of simulating intracardiac blood flow gives a base for the understanding of different morphopathologies and their impact on intraventricular flow patterns. In contrast to medical flow imaging (e.g. MRI, Colour-Doppler-echocardiography) the numerical flow model enables us to perform intraventricular energy estimations. With this tool, pathomorphological changes as well as therapies affecting intraventricular flow can qualitatively be juged. Future aspects of our project comprise a virtual therapy planning system. References [1] H. Oertel: Biofluid Mechanics of Blood Circulation, in: Prandtl's Essentials of Fluid Mechanics, Springer, New York 2004.
4726 Th, 08:45-09:00 (P38) Comparison of measured and simulated deformation of a left ventricle M.B. Mohr 1, G. Seemann 1, EB. Sachse 2, B. Jung 3, O. D6ssel 1. 1Institute of Biomedical Engineering, Universitat Karlsruhe (TH), Germany, 2Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, USA, 3University Hospital Freiburg, Department of Diagnostic Radiology Medical Physics, Freiburg, Germany Today only imaging techniques support medical doctors for surgery planning in cardiology. This work contributes a step towards 4D modelling of the heart of individual patients to describe the elastomechanical behavior of myocardial tissue. This model can support the planning of cardiac surgery. The model is a based on a spring-mass system in conjunction with continuum mechanical methods. MRI data of the left ventricle of a healthy volunteer were acquired for 800 ms at an 14ms interval. The data recorded at the R peak of the ECG was used as geometrical model of the left ventricle shortly before systole. For mechanical simulation a rule based fiber orientation was included into the model reconstructing physiological measurements. A contraction initiating force distribution was computed with a cellular automaton parameterized by detailed electrophysiological simulations. The vertical motion of the models apex was restricted. The deformation of the left ventricular model was computed and compared to the deformations recorded by measurements. Parameters of the mechanical model were adapted to receive similar circumferential contraction. The MRI data did not include vertical motion of the ventricle. Therefore, a comparison of the apical basal contraction was not possible. The application of a patient data into the mechanical model was accomplished and resulted in adequate deformations. The comparison of measured and simulated ventricular deformation showed an asymmetrical circumferential contraction of the measured ventricle whereas the simulation was more homogeneous. In addition, the thickening of the wall during contraction as well as the speed of relaxation of the simulation was slightly smaller compared to the measured data. Differences of deformation can be accounted to non-realistic boundary condition such as fixation of the venticle at the pericardial sac and connection with the right ventricle.
14.6. Computational Modelling
$297
5052 Th, 09:00-09:15 (P39) Hemorheological properties effects on wall shear stress computation: analysis for intra-stent flow N. B6nard 1, R. Perrault 1, D. Coisne 1,2. 1Laboratoire d'Etudes A6rodynamiques, Poitiers, France, 2 University Hospital La mil6trie, Cardiology unit, Poitiers, France Influence of blood rheological properties on normal or pathological coronary flow have been widely studied. Few data are available in case of coronary stented arteries. After endoprotheses implantation, knowledge of wall shear stress values (WSS), greatly dependent of local viscosity, is of primary importance for estimating neo intimal proliferation and restenosis risk. Our work contributes to estimate the impact of hemorheology on WSS. The refined 3D mesh of a real stent model placed in a straight and rigid coronary artery was introduced into a commercial computer code (Star-Cd). Steady-state simulations were conducted to compare WSS fields resulting from imposing minimum and peak flow values issued from a left coronary artery. Three rheological assumptions were then numerically introduced: a newtonian assumption (~t =3.7cP), a Cross-modified model based on physiological data and a characteristic viscosity. With the Cross-modified model reproducing the physiological blood shear thinning properties, wall viscosities were ever superior to the traditional newtonian viscosity. In consequence, if the WSS fields were qualitatively similar, we noticed significant quantitative variations. The mean ratios between non newtonian and newtonian WSS were of 1.6 and 2.6 respectively for the central part and the surface surrounding wire (high and low WSS). Interpretation consequences of WSS issued from a newtonian assumption are a systematic overestimation of the restenosis risk area. A characteristic viscosity allows moderating these ratios with WSS results very close to those obtained with physiological blood behaviour and an important CPU time consuming gain. Beyond characterizing the WSS fields and the impact of hemorheology on WSS for a stented coronary flow, this study introduces an alternative to traditional newtonian rheological modelling. The defined characteristic viscosity allows increasing accuracy of numerical WSS determination compared to standard newtonian assumption. 6912 Th, 09:15-09:30 (P39) Finite element simulation of the free expansion of the Cypher stent crimped on a tri-folded balloon M. De Beule 1, P. Mortier 1, P. Segers 2, S.G. Carlier3, B. Verhegghe 4, R. Van Impe 1, E Verdonck 2. 1Laboratory for Research on Structural Models, Ghent University, Belgium, 2 Cardiovascular Mechanics and Biofluid Dynamics research Unit, Institute Biomedical Technology, Ghent University, Belgium, 3Colombia University Medical Center, New York, USA, 4Department of Mechanical Construction and Production, Ghent University, Belgium Background: Stents are slotted tubes which are deployed in an obstructed artery to restore normal blood flow. The stents are crimped on a folded balloon to have a low profile for deliverability and lesion access. Several studies have exploited the finite element method to gain insight in their mechanical behaviour or to study the vascular reaction to stent deployment. However, to date - to the best of our knowledge - the inflation balloon is either discarded from those simulations, or simplified by assuming it to have a cylindrical shape. Methods: The free expansion of the CYPHER TM coronary stent (length 8 mm, diameter 3 mm; Cordis, Johnson & Johnson, Waterloo, Belgium) is simulated following 2 scenarios: (i) accounting for balloon-stent interaction and applying an increasing uniform pressure up to 1.5N/mm 2 on the inner surface of a tri-folded duralyn ® RAPTOR TM balloon (length 10mm, diameter 3mm); (ii) ignoring the balloon and applying the same pressure directly to the stent inner surface. The key features of the analysis performed using ABAQUS are the presence of non-linearities, large deformations and (self) contact. Results and Conclusions: Accounting for the presence of the balloon reveals a particular deployment pattern in the low pressure range (<0.3 N/mm 2) driven by the unfolding of the balloon and ensures a very close agreement between the simulated and reference pressure - diameter relationship (provided by the manufacturer). The maximum percent difference in diameter occurs at a pressure of 0.6 N/mm 2 and is an overestimation of 5.7%. Discarding the balloon leads to an underestimation of 62.6% of the diameter at 0.6 N/mm 2. Our model may be the basis for the generation of new realistic computational models of angioplasty procedures as well as a platform to assess struts / vessel wall interactions and stent struts distribution.
and is shifted for higher values of pressure if the wall thickness is increased. Our results are in agreement with experimental observations. 7027 Th, 08:30-08:45 (P38) Computational simulation of blood flow in the human left ventricle W. Schiller 1, T. Schmid 3, K. Spiegel 2, S. Donisi 2, C. Probst 1, A. Kovacz 4, S. Flacke 4, D. Liepsch 3, H. Oertel 2 . 1KIinik und Poliklinik for Herzchirurgie, Universit#t Bonn, Germany, 21nstitut for Str6mungslehre, Universit#t Karlsruhe, Germany, 3Lehrstuhl for Str6mungsmechanik, Fachhochschule MEtnchen, Germany, 4Radiologische Klinik, Universit#t Bonn, Germany Aim of our project was to simulate intracardiac blood flow in the human left heart to reveal changes in flow patterns and energy losses depending on different pathologies. The presented virtual heart model is based on data from real human hearts. Magnetique Resonance Imaging (MRI) was used to get time-depending geometry and intraventricular flow from healthy and pathological human left ventricles and the adjacent left atrium. After segmentation and post processing of the data, a preformed aorta and heart valves as passive components were inserted and coupled to the model. The numerical flow calculation was performed with a finite volume method. Boundary conditions such as preand afterload were given by a simplified circulation model. An experimental validation comprising flow measurements (LDA- and PIV-measurements) in a silicone ventricle which represents the exact geometry of the virtual ventricle showed high correlation to the computational flow simulation. The comparison of MRI -flow measurements and numerical simulation data revealed the impact of procedural influences such as MRI scanning, segmentation and postprocessing. The developed method of simulating intracardiac blood flow gives a base for the understanding of different morphopathologies and their impact on intraventricular flow patterns. In contrast to medical flow imaging (e.g. MRI, Colour-Doppler-echocardiography) the numerical flow model enables us to perform intraventricular energy estimations. With this tool, pathomorphological changes as well as therapies affecting intraventricular flow can qualitatively be juged. Future aspects of our project comprise a virtual therapy planning system. References [1] H. Oertel: Biofluid Mechanics of Blood Circulation, in: Prandtl's Essentials of Fluid Mechanics, Springer, New York 2004.
4726 Th, 08:45-09:00 (P38) Comparison of measured and simulated deformation of a left ventricle M.B. Mohr 1, G. Seemann 1, EB. Sachse 2, B. Jung 3, O. D6ssel 1. 1Institute of Biomedical Engineering, Universitat Karlsruhe (TH), Germany, 2Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, USA, 3University Hospital Freiburg, Department of Diagnostic Radiology Medical Physics, Freiburg, Germany Today only imaging techniques support medical doctors for surgery planning in cardiology. This work contributes a step towards 4D modelling of the heart of individual patients to describe the elastomechanical behavior of myocardial tissue. This model can support the planning of cardiac surgery. The model is a based on a spring-mass system in conjunction with continuum mechanical methods. MRI data of the left ventricle of a healthy volunteer were acquired for 800 ms at an 14ms interval. The data recorded at the R peak of the ECG was used as geometrical model of the left ventricle shortly before systole. For mechanical simulation a rule based fiber orientation was included into the model reconstructing physiological measurements. A contraction initiating force distribution was computed with a cellular automaton parameterized by detailed electrophysiological simulations. The vertical motion of the models apex was restricted. The deformation of the left ventricular model was computed and compared to the deformations recorded by measurements. Parameters of the mechanical model were adapted to receive similar circumferential contraction. The MRI data did not include vertical motion of the ventricle. Therefore, a comparison of the apical basal contraction was not possible. The application of a patient data into the mechanical model was accomplished and resulted in adequate deformations. The comparison of measured and simulated ventricular deformation showed an asymmetrical circumferential contraction of the measured ventricle whereas the simulation was more homogeneous. In addition, the thickening of the wall during contraction as well as the speed of relaxation of the simulation was slightly smaller compared to the measured data. Differences of deformation can be accounted to non-realistic boundary condition such as fixation of the venticle at the pericardial sac and connection with the right ventricle.
14.6. Computational Modelling
$297
5052 Th, 09:00-09:15 (P39) Hemorheological properties effects on wall shear stress computation: analysis for intra-stent flow N. B6nard 1, R. Perrault 1, D. Coisne 1,2. 1Laboratoire d'Etudes A6rodynamiques, Poitiers, France, 2 University Hospital La mil6trie, Cardiology unit, Poitiers, France Influence of blood rheological properties on normal or pathological coronary flow have been widely studied. Few data are available in case of coronary stented arteries. After endoprotheses implantation, knowledge of wall shear stress values (WSS), greatly dependent of local viscosity, is of primary importance for estimating neo intimal proliferation and restenosis risk. Our work contributes to estimate the impact of hemorheology on WSS. The refined 3D mesh of a real stent model placed in a straight and rigid coronary artery was introduced into a commercial computer code (Star-Cd). Steady-state simulations were conducted to compare WSS fields resulting from imposing minimum and peak flow values issued from a left coronary artery. Three rheological assumptions were then numerically introduced: a newtonian assumption (~t =3.7cP), a Cross-modified model based on physiological data and a characteristic viscosity. With the Cross-modified model reproducing the physiological blood shear thinning properties, wall viscosities were ever superior to the traditional newtonian viscosity. In consequence, if the WSS fields were qualitatively similar, we noticed significant quantitative variations. The mean ratios between non newtonian and newtonian WSS were of 1.6 and 2.6 respectively for the central part and the surface surrounding wire (high and low WSS). Interpretation consequences of WSS issued from a newtonian assumption are a systematic overestimation of the restenosis risk area. A characteristic viscosity allows moderating these ratios with WSS results very close to those obtained with physiological blood behaviour and an important CPU time consuming gain. Beyond characterizing the WSS fields and the impact of hemorheology on WSS for a stented coronary flow, this study introduces an alternative to traditional newtonian rheological modelling. The defined characteristic viscosity allows increasing accuracy of numerical WSS determination compared to standard newtonian assumption. 6912 Th, 09:15-09:30 (P39) Finite element simulation of the free expansion of the Cypher stent crimped on a tri-folded balloon M. De Beule 1, P. Mortier 1, P. Segers 2, S.G. Carlier3, B. Verhegghe 4, R. Van Impe 1, E Verdonck 2. 1Laboratory for Research on Structural Models, Ghent University, Belgium, 2 Cardiovascular Mechanics and Biofluid Dynamics research Unit, Institute Biomedical Technology, Ghent University, Belgium, 3Colombia University Medical Center, New York, USA, 4Department of Mechanical Construction and Production, Ghent University, Belgium Background: Stents are slotted tubes which are deployed in an obstructed artery to restore normal blood flow. The stents are crimped on a folded balloon to have a low profile for deliverability and lesion access. Several studies have exploited the finite element method to gain insight in their mechanical behaviour or to study the vascular reaction to stent deployment. However, to date - to the best of our knowledge - the inflation balloon is either discarded from those simulations, or simplified by assuming it to have a cylindrical shape. Methods: The free expansion of the CYPHER TM coronary stent (length 8 mm, diameter 3 mm; Cordis, Johnson & Johnson, Waterloo, Belgium) is simulated following 2 scenarios: (i) accounting for balloon-stent interaction and applying an increasing uniform pressure up to 1.5N/mm 2 on the inner surface of a tri-folded duralyn ® RAPTOR TM balloon (length 10mm, diameter 3mm); (ii) ignoring the balloon and applying the same pressure directly to the stent inner surface. The key features of the analysis performed using ABAQUS are the presence of non-linearities, large deformations and (self) contact. Results and Conclusions: Accounting for the presence of the balloon reveals a particular deployment pattern in the low pressure range (<0.3 N/mm 2) driven by the unfolding of the balloon and ensures a very close agreement between the simulated and reference pressure - diameter relationship (provided by the manufacturer). The maximum percent difference in diameter occurs at a pressure of 0.6 N/mm 2 and is an overestimation of 5.7%. Discarding the balloon leads to an underestimation of 62.6% of the diameter at 0.6 N/mm 2. Our model may be the basis for the generation of new realistic computational models of angioplasty procedures as well as a platform to assess struts / vessel wall interactions and stent struts distribution.