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Ghassan S Kassab - One of the best experts on this subject based on the ideXlab platform.

  • hemodynamics in coronary Arterial Tree of serial stenoses
    PLOS ONE, 2016
    Co-Authors: Xi Chen, Bin Lu, Liang Zhong-yu, Ghassan S Kassab
    Abstract:

    : Serial segmental narrowing frequently occurs in humans, which alters coronary hemodynamics and further affects atherosclerotic progression and plaque formation. The objective of this study was to understand the distribution of hemodynamic parameters in the epicardial left main coronary Arterial (LMCA) Tree with serial stenoses reconstructed from patient computer tomography angiography (CTA) images. A finite volume method was used in conjunction with the inlet pressure wave and outlet flow resistance. The time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) were determined from the flow field. A stenosis at a mother vessel mainly deteriorated the hemodynamics near the bifurcation while a stenosis at a daughter vessel affected the remote downstream bifurcation. In comparison with a single stenosis, serial stenoses increased the peak pressure gradient along the main trunk of the epicardial left anterior descending Arterial Tree by > 50%. An increased distance between serial stenoses further increased the peak pressure gradient. These findings have important implications on the diagnosis and treatment of serial coronary stenoses.

  • effect of compliance and hematocrit on wall shear stress in a model of the entire coronary Arterial Tree
    Journal of Applied Physiology, 2009
    Co-Authors: Yunlong Huo, Ghassan S Kassab
    Abstract:

    A hemodynamic analysis is implemented in the entire coronary Arterial Tree of diastolically arrested, vasodilated pig heart that takes into account vessel compliance and blood viscosity in each ves...

  • flow patterns in three dimensional porcine epicardial coronary Arterial Tree
    American Journal of Physiology-heart and Circulatory Physiology, 2007
    Co-Authors: Yunlong Huo, Thomas Wischgoll, Ghassan S Kassab
    Abstract:

    The branching pattern of epicardial coronary arteries is clearly three-dimensional, with correspondingly complex flow patterns. The objective of the present study was to perform a detailed hemodynamic analysis using a three-dimensional finite element method in a left anterior descending (LAD) epicardial Arterial Tree, including main trunk and primary branches, based on computed tomography scans. The inlet LAD flow velocity was measured in an anesthetized pig, and the outlet pressure boundary condition was estimated based on scaling laws. The spatial and temporal wall shear stress (WSS), gradient of WSS (WSSG), and oscillatory shear index (OSI) were calculated and used to identify regions of flow disturbances in the vicinity of primary bifurcations. We found that low WSS and high OSI coincide with disturbed flows (stagnated, secondary, and reversed flows) opposite to the flow divider and lateral to the junction orifice of the main trunk and primary branches. High time-averaged WSSG occurs in regions of bifurcations, with the flow divider having maximum values. Low WSS and high OSI were found to be related through a power law relationship. Furthermore, zones of low time-averaged WSS and high OSI amplified for larger diameter ratio and high inlet flow rate. Hence, different focal atherosclerotic-prone regions may be explained by different physical mechanism associated with certain critical levels of low WSS, high OSI, and high WSSG, which are strongly affected by the diameter ratio. The implications of the flow patterns for atherogenesis are enumerated.

  • a hybrid one dimensional womersley model of pulsatile blood flow in the entire coronary Arterial Tree
    American Journal of Physiology-heart and Circulatory Physiology, 2007
    Co-Authors: Ghassan S Kassab
    Abstract:

    Using a frequency-domain Womersley-type model, we previously simulated pulsatile blood flow throughout the coronary Arterial Tree. Although this model represents a good approximation for the smalle...

  • a hybrid one dimensional womersley model of pulsatile blood flow in the entire coronary Arterial Tree
    American Journal of Physiology-heart and Circulatory Physiology, 2007
    Co-Authors: Yunlong Huo, Ghassan S Kassab
    Abstract:

    Using a frequency-domain Womersley-type model, we previously simulated pulsatile blood flow throughout the coronary Arterial Tree. Although this model represents a good approximation for the smaller vessels, it does not take into account the nonlinear convective energy losses in larger vessels. Here, using Womersley's theory, we present a hybrid model that considers the nonlinear effects for the larger epicardial arteries while simulating the distal vessels (down to the 1st capillary segments) with the use of Womersley's Theory. The main trunk and primary branches were discretized and modeled with one-dimensional Navier-Stokes equations, while the smaller-diameter vessels were treated as Womersley-type vessels. Energy losses associated with vessel bifurcations were incorporated in the present analysis. The formulation enables prediction of impedance and pressure and pulsatile flow distribution throughout the entire coronary Arterial Tree down to the first capillary segments in the arrested, vasodilated state. We found that the nonlinear convective term is negligible and the loss of energy at a bifurcation is small in the larger epicardial vessels of an arrested heart. Furthermore, we found that the flow waves along the trunk or at the primary branches tend to scale (normalized with respect to their mean values) to a single curve, except for a small phase angle difference. Finally, the model predictions for the inlet pressure and flow waves are in excellent agreement with previously published experimental results. This hybrid one-dimensional/Womersley model is an efficient approach that captures the essence of the hemodynamics of a complex large-scale vascular network. The present model has numerous applications to understanding the dynamics of coronary circulation.

Yunlong Huo - One of the best experts on this subject based on the ideXlab platform.

  • effect of compliance and hematocrit on wall shear stress in a model of the entire coronary Arterial Tree
    Journal of Applied Physiology, 2009
    Co-Authors: Yunlong Huo, Ghassan S Kassab
    Abstract:

    A hemodynamic analysis is implemented in the entire coronary Arterial Tree of diastolically arrested, vasodilated pig heart that takes into account vessel compliance and blood viscosity in each ves...

  • flow patterns in three dimensional porcine epicardial coronary Arterial Tree
    American Journal of Physiology-heart and Circulatory Physiology, 2007
    Co-Authors: Yunlong Huo, Thomas Wischgoll, Ghassan S Kassab
    Abstract:

    The branching pattern of epicardial coronary arteries is clearly three-dimensional, with correspondingly complex flow patterns. The objective of the present study was to perform a detailed hemodynamic analysis using a three-dimensional finite element method in a left anterior descending (LAD) epicardial Arterial Tree, including main trunk and primary branches, based on computed tomography scans. The inlet LAD flow velocity was measured in an anesthetized pig, and the outlet pressure boundary condition was estimated based on scaling laws. The spatial and temporal wall shear stress (WSS), gradient of WSS (WSSG), and oscillatory shear index (OSI) were calculated and used to identify regions of flow disturbances in the vicinity of primary bifurcations. We found that low WSS and high OSI coincide with disturbed flows (stagnated, secondary, and reversed flows) opposite to the flow divider and lateral to the junction orifice of the main trunk and primary branches. High time-averaged WSSG occurs in regions of bifurcations, with the flow divider having maximum values. Low WSS and high OSI were found to be related through a power law relationship. Furthermore, zones of low time-averaged WSS and high OSI amplified for larger diameter ratio and high inlet flow rate. Hence, different focal atherosclerotic-prone regions may be explained by different physical mechanism associated with certain critical levels of low WSS, high OSI, and high WSSG, which are strongly affected by the diameter ratio. The implications of the flow patterns for atherogenesis are enumerated.

  • a hybrid one dimensional womersley model of pulsatile blood flow in the entire coronary Arterial Tree
    American Journal of Physiology-heart and Circulatory Physiology, 2007
    Co-Authors: Yunlong Huo, Ghassan S Kassab
    Abstract:

    Using a frequency-domain Womersley-type model, we previously simulated pulsatile blood flow throughout the coronary Arterial Tree. Although this model represents a good approximation for the smaller vessels, it does not take into account the nonlinear convective energy losses in larger vessels. Here, using Womersley's theory, we present a hybrid model that considers the nonlinear effects for the larger epicardial arteries while simulating the distal vessels (down to the 1st capillary segments) with the use of Womersley's Theory. The main trunk and primary branches were discretized and modeled with one-dimensional Navier-Stokes equations, while the smaller-diameter vessels were treated as Womersley-type vessels. Energy losses associated with vessel bifurcations were incorporated in the present analysis. The formulation enables prediction of impedance and pressure and pulsatile flow distribution throughout the entire coronary Arterial Tree down to the first capillary segments in the arrested, vasodilated state. We found that the nonlinear convective term is negligible and the loss of energy at a bifurcation is small in the larger epicardial vessels of an arrested heart. Furthermore, we found that the flow waves along the trunk or at the primary branches tend to scale (normalized with respect to their mean values) to a single curve, except for a small phase angle difference. Finally, the model predictions for the inlet pressure and flow waves are in excellent agreement with previously published experimental results. This hybrid one-dimensional/Womersley model is an efficient approach that captures the essence of the hemodynamics of a complex large-scale vascular network. The present model has numerous applications to understanding the dynamics of coronary circulation.

  • pulsatile blood flow in the entire coronary Arterial Tree theory and experiment
    American Journal of Physiology-heart and Circulatory Physiology, 2006
    Co-Authors: Yunlong Huo, Ghassan S Kassab
    Abstract:

    The pulsatility of coronary circulation can be accurately simulated on the basis of the measured branching pattern, vascular geometry, and material properties of the coronary vasculature. A Womersley-type mathematical model is developed to analyze pulsatile blood flow in diastole in the absence of vessel tone in the entire coronary Arterial Tree on the basis of previously measured morphometric data. The model incorporates a constitutive equation of pressure and cross-section area relation based on our previous experimental data. The formulation enables the prediction of the impedance, the pressure distribution, and the pulsatile flow distribution throughout the entire coronary Arterial Tree. The model is validated by experimental measurements in six diastolic arrested, vasodilated porcine hearts. The agreement between theory and experiment is excellent. Furthermore, the present pulse wave results at low frequency agree very well with previously published steady-state model. Finally, the phase angle of flow is seen to decrease along the trunk of the major coronary artery and primary branches toward the capillary vessels. This study represents the first, most extensive validated analysis of Womersley-type pulse wave transmission in the entire coronary Arterial Tree down to the first segment of capillaries. The present model will serve to quantitatively test various hypotheses in the coronary circulation under pulsatile flow conditions.

Sabee Molloi - One of the best experts on this subject based on the ideXlab platform.

  • regional blood flow analysis and its relationship with Arterial branch lengths and lumen volume in the coronary Arterial Tree
    Physics in Medicine and Biology, 2007
    Co-Authors: Sabee Molloi, Jerry T Wong
    Abstract:

    The limitations of visually assessing coronary artery disease are well known. These limitations are particularly important in intermediate coronary lesions (30–70% diameter stenosis) where it is difficult to determine whether a particular lesion is the cause of ischaemia. Therefore, a functional measure of stenosis severity is needed. The purpose of this study is to determine whether the expected maximum coronary blood flow in an Arterial Tree is predictable from its sum of Arterial branch lengths or lumen volume. Using a computer model of a porcine coronary artery Tree, an analysis of blood flow distribution was conducted through a network of millions of vessels that included the entire coronary artery Tree down to the first capillary branch. The flow simulation results show that there is a linear relationship between coronary blood flow and the sum of its Arterial branch lengths. This relationship holds over the entire Arterial Tree. The flow simulation results also indicate that there is a power relation between coronary blood flow (Q) and the sum of its Arterial lumen volume (V). Moreover, there is a linear relationship between normalized Q and normalized V raised to a power of over the entire Arterial Tree. These results indicate that measured Arterial branch lengths or lumen volumes can be used to predict the expected maximum blood flow in an Arterial Tree. This theoretical maximum blood flow, in conjunction with an angiographically measured blood flow, can potentially be used to calculate fractional flow reserve based entirely on angiographic data.

  • a computer reconstruction of the entire coronary Arterial Tree based on detailed morphometric data
    Annals of Biomedical Engineering, 2005
    Co-Authors: N Mittal, Sabee Molloi, Yifang Zhou, S Ung, Carlos Linares, Ghassan S Kassab
    Abstract:

    A rigorous analysis of blood flow must be based on the branching pattern and vascular geometry of the full vascular circuit of interest. It is experimentally difficult to reconstruct the entire vascular circuit of any organ because of the enormity of the vessels. The objective of the present study was to develop a novel method for the reconstruction of the full coronary vascular Tree from partial measurements. Our method includes the use of data on those parts of the Tree that are measured to extrapolate the data on those parts that are missing. Specifically, a two-step approach was employed in the reconstruction of the entire coronary Arterial Tree down to the capillary level. Vessels > 40 microm were reconstructed from cast data while vessels < 40 microm were reconstructed from histological data. The cast data were reconstructed one-bifurcation at a time while histological data were reconstructed one-sub-Tree at a time by "cutting" and "pasting" of data from measured to missing vessels. The reconstruction algorithm yielded a full Arterial Tree down to the first capillary bifurcation with 1.9, 2.04 and 1.15 million vessel segments for the right coronary artery (RCA), left anterior descending (LAD) and left circumflex (LCx) Trees, respectively. The node-to-node connectivity along with the diameter and length of every vessel segment was determined. Once the full Tree was reconstructed, we automated the assignment of order numbers, according to the diameter-defined Strahler system, to every vessel segment in the Tree. Consequently, the diameters, lengths, number of vessels, segments-per-element ratio, connectivity and longitudinal matrices were determined for every order number. The present model establishes a morphological foundation for future analysis of blood flow in the coronary circulation.

  • analysis of blood flow in the entire coronary Arterial Tree
    American Journal of Physiology-heart and Circulatory Physiology, 2005
    Co-Authors: N Mittal, Benjamin Kaimovitz, Sabee Molloi, Yifang Zhou, S Ung, Carlos Linares, Ghassan S Kassab
    Abstract:

    A hemodynamic analysis of coronary blood flow must be based on the measured branching pattern and vascular geometry of the coronary vasculature. We recently developed a computer reconstruction of t...

  • on the design of the coronary Arterial Tree a generalization of murray s law
    Physics in Medicine and Biology, 1999
    Co-Authors: Yifang Zhou, Ghassan S Kassab, Sabee Molloi
    Abstract:

    Murray's law has been generalized to provide morphometric relationships among various subTrees as well as between a feeding segment and the subTree it perfuses. The equivalent resistance of each subTree is empirically determined to be proportional to the cube of a subTree's cumulative Arterial length (L) and inversely proportional to a subTree's Arterial volume (V) raised to a power of approximately 2.6. This relationship, along with a minimization of a cost function, and a linearity assumption between flow and cumulative Arterial length, provides a power law relationship between V and L. These results, in conjunction with conservation of energy, yield relationships between the diameter of a segment and the length of its distal subTree. The relationships were tested based on a complete set of anatomical data of the coronary Arterial Trees using two models. The first model, called the truncated Tree model, is an actual reconstruction of the coronary Arterial Tree down to 500 µm in diameter. The second model, called the symmetric Tree model, satisfies all mean anatomical data down to the capillary vessels. Our results show very good agreement between the theoretical formulation and the measured anatomical data, which may provide insight into the design of the coronary Arterial Tree. Furthermore, the established relationships between the various morphometric parameters of the truncated Tree model may provide a basis for assessing the extent of diffuse coronary artery disease.

B M W Tsui - One of the best experts on this subject based on the ideXlab platform.

  • development of a model of the coronary Arterial Tree for the 4d xcat phantom
    Physics in Medicine and Biology, 2011
    Co-Authors: George S K Fung, Paul W Segars, Grant T Gullberg, B M W Tsui
    Abstract:

    A detailed three-dimensional (3D) model of the coronary artery Tree with cardiac motion has great potential for applications in a wide variety of medical imaging research areas. In this work, we first developed a computer-generated 3D model of the coronary Arterial Tree for the heart in the extended cardiac-torso (XCAT) phantom, thereby creating a realistic computer model of the human anatomy. The coronary Arterial Tree model was based on two datasets: (1) a gated cardiac dual-source computed tomography (CT) angiographic dataset obtained from a normal human subject and (2) statistical morphometric data of porcine hearts. The initial proximal segments of the vasculature and the anatomical details of the boundaries of the ventricles were defined by segmenting the CT data. An iterative rule-based generation method was developed and applied to extend the coronary Arterial Tree beyond the initial proximal segments. The algorithm was governed by three factors: (1) statistical morphometric measurements of the connectivity, lengths and diameters of the Arterial segments; (2) avoidance forces from other vessel segments and the boundaries of the myocardium, and (3) optimality principles which minimize the drag force at the bifurcations of the generated Tree. Using this algorithm, the 3D computational model of the largest six orders of the coronary Arterial Tree was generated, which spread across the myocardium of the left and right ventricles. The 3D coronary Arterial Tree model was then extended to 4D to simulate different cardiac phases by deforming the original 3D model according to the motion vector map of the 4D cardiac model of the XCAT phantom at the corresponding phases. As a result, a detailed and realistic 4D model of the coronary Arterial Tree was developed for the XCAT phantom by imposing constraints of anatomical and physiological characteristics of the coronary vasculature. This new 4D coronary artery Tree model provides a unique simulation tool that can be used in the development and evaluation of instrumentation and methods for imaging normal and pathological hearts with myocardial perfusion defects.

  • toward modeling of regional myocardial ischemia and infarction generation of realistic coronary Arterial Tree for the heart model of the xcat phantom
    Proceedings of SPIE, 2009
    Co-Authors: George S K Fung, Paul W Segars, Grant T Gullberg, Alexander I Veress, B M W Tsui
    Abstract:

    A realistic 3D coronary Arterial Tree (CAT) has been developed for the heart model of the computer generated 3D XCAT phantom. The CAT allows generation of a realistic model of the location, size and shape of the associated regional ischemia or infarction for a given coronary Arterial stenosis or occlusion. This in turn can be used in medical imaging applications. An iterative rule-based generation method that systematically utilized anatomic, morphometric and physiologic knowledge was used to construct a detailed realistic 3D model of the CAT in the XCAT phantom. The anatomic details of the myocardial surfaces and large coronary Arterial vessel segments were first extracted from cardiac CT images of a normal patient with right coronary dominance. Morphometric information derived from porcine data from the literature, after being adjusted by scaling laws, provided statistically nominal diameters, lengths, and connectivity probabilities of the generated coronary Arterial segments in modeling the CAT of an average human. The largest six orders of the CAT were generated based on the physiologic constraints defined in the coronary generation algorithms. When combined with the heart model of the XCAT phantom, the realistic CAT provides a unique simulation tool for the generation of realistic regional myocardial ischemia and infraction. Together with the existing heart model, the new CAT provides an important improvement over the current 3D XCAT phantom in providing a more realistic model of the normal heart and the potential to simulate myocardial diseases in evaluation of medical imaging instrumentation, image reconstruction, and data processing methods.

  • development of a computer generated model for the coronary Arterial Tree based on multislice ct and morphometric data
    Medical Imaging 2006: Physics of Medical Imaging, 2006
    Co-Authors: George S K Fung, Paul W Segars, Katsuyuki Taguchi, Elliot K Fishman, B M W Tsui
    Abstract:

    A detailed four-dimensional model of the coronary artery Tree has great potential in a wide variety of applications especially in biomedical imaging. We developed a computer generated three-dimensional model for the coronary Arterial Tree based on two datasets: (1) gated multi-slice computed tomography (MSCT) angiographic data obtained from a normal human subject and (2) statistical morphometric data obtained from porcine hearts. The main coronary arteries and heart structures were segmented from the MSCT data to define the initial segments of the vasculature and geometrical details of the boundaries. An iterative rule-based computer generation algorithm was then developed to extend the coronary artery Tree beyond the initial segmented branches. The algorithm was governed by the following factors: (1) the statistical morphometric measurements of the connectivities, lengths, and diameters of the Arterial segments, (2) repelling forces from other segments and boundaries, and (3) optimality principles to minimize the drag force at each bifurcation in the generated Tree. Using this algorithm, the segmented coronary artery Tree from the MSCT data was optimally extended to create a 3D computational model of the largest six orders of the coronary Arterial Tree. The new method for generating the 3D model is effective in imposing the constraints of anatomical and physiological characteristics of coronary vasculature. When combined with the 4D NCAT phantom, a computer model for the human anatomy and cardiac and respiratory motions, the new model will provide a unique tool to study cardiovascular characteristics and diseases through direct and medical imaging simulation studies.

Yifang Zhou - One of the best experts on this subject based on the ideXlab platform.

  • a computer reconstruction of the entire coronary Arterial Tree based on detailed morphometric data
    Annals of Biomedical Engineering, 2005
    Co-Authors: N Mittal, Sabee Molloi, Yifang Zhou, S Ung, Carlos Linares, Ghassan S Kassab
    Abstract:

    A rigorous analysis of blood flow must be based on the branching pattern and vascular geometry of the full vascular circuit of interest. It is experimentally difficult to reconstruct the entire vascular circuit of any organ because of the enormity of the vessels. The objective of the present study was to develop a novel method for the reconstruction of the full coronary vascular Tree from partial measurements. Our method includes the use of data on those parts of the Tree that are measured to extrapolate the data on those parts that are missing. Specifically, a two-step approach was employed in the reconstruction of the entire coronary Arterial Tree down to the capillary level. Vessels > 40 microm were reconstructed from cast data while vessels < 40 microm were reconstructed from histological data. The cast data were reconstructed one-bifurcation at a time while histological data were reconstructed one-sub-Tree at a time by "cutting" and "pasting" of data from measured to missing vessels. The reconstruction algorithm yielded a full Arterial Tree down to the first capillary bifurcation with 1.9, 2.04 and 1.15 million vessel segments for the right coronary artery (RCA), left anterior descending (LAD) and left circumflex (LCx) Trees, respectively. The node-to-node connectivity along with the diameter and length of every vessel segment was determined. Once the full Tree was reconstructed, we automated the assignment of order numbers, according to the diameter-defined Strahler system, to every vessel segment in the Tree. Consequently, the diameters, lengths, number of vessels, segments-per-element ratio, connectivity and longitudinal matrices were determined for every order number. The present model establishes a morphological foundation for future analysis of blood flow in the coronary circulation.

  • analysis of blood flow in the entire coronary Arterial Tree
    American Journal of Physiology-heart and Circulatory Physiology, 2005
    Co-Authors: N Mittal, Benjamin Kaimovitz, Sabee Molloi, Yifang Zhou, S Ung, Carlos Linares, Ghassan S Kassab
    Abstract:

    A hemodynamic analysis of coronary blood flow must be based on the measured branching pattern and vascular geometry of the coronary vasculature. We recently developed a computer reconstruction of t...

  • on the design of the coronary Arterial Tree a generalization of murray s law
    Physics in Medicine and Biology, 1999
    Co-Authors: Yifang Zhou, Ghassan S Kassab, Sabee Molloi
    Abstract:

    Murray's law has been generalized to provide morphometric relationships among various subTrees as well as between a feeding segment and the subTree it perfuses. The equivalent resistance of each subTree is empirically determined to be proportional to the cube of a subTree's cumulative Arterial length (L) and inversely proportional to a subTree's Arterial volume (V) raised to a power of approximately 2.6. This relationship, along with a minimization of a cost function, and a linearity assumption between flow and cumulative Arterial length, provides a power law relationship between V and L. These results, in conjunction with conservation of energy, yield relationships between the diameter of a segment and the length of its distal subTree. The relationships were tested based on a complete set of anatomical data of the coronary Arterial Trees using two models. The first model, called the truncated Tree model, is an actual reconstruction of the coronary Arterial Tree down to 500 µm in diameter. The second model, called the symmetric Tree model, satisfies all mean anatomical data down to the capillary vessels. Our results show very good agreement between the theoretical formulation and the measured anatomical data, which may provide insight into the design of the coronary Arterial Tree. Furthermore, the established relationships between the various morphometric parameters of the truncated Tree model may provide a basis for assessing the extent of diffuse coronary artery disease.