Patient-specific Blood Flow Simulation Research Articles

Hemodynamics in Coronary Arteries: using Open-Source Software-Simvascular to Investigate the Hemodynamics in Coronary Arteries of the Patient-Specific Modeling

Patient-specific cardiovascular simulation is emerging as a potent tool for basic, translational, and clinical research and has established itself as a paradigm in the field of cardiovascular science. The SimVascular software package, considered a state-of-the-art open-source package, offers a comprehensive pipeline from medical imaging data segmentation to patient-specific blood flow simulation and analysis. In this study, we employ SimVascular to explore a model of coronary arteries in a young and healthy 24-year-old woman. The outcomes of the entire simulation process encompass the assessment of flow and pressure waveforms at both the outlet of the aorta and the coronary arteries, which serve as indicators of blood flow qualities within these vessels. Given the pivotal role of wall shear stress in the development of arterial plaque, SimVascular employs the finite element method to solve the governing equations of incompressible viscous fluids. This approach effectively tackles the Navier-Stokes equations along the vessel wall using meticulously constructed mesh components. Additionally, this paper delves into the issue of cardiovascular blood vessel dynamics via an analysis of wall shear stress data).

Abstract WP137: A CT Perfusion Based Computational Modeling for Improved Risk Stratification of Haemodynamically Significant ICAD

Aim: In endovascular ICAD treatment, an individualized patient-specific treatment pathway may be very helpful. Patient selection for endovascular treatment based on anatomical markers has not been shown to be effective in past clinical trials. This pilot study combines CT perfusion (CTP) analysis and computational fluid dynamics to identify hemodynamically significant patients for a reliable pathway for intervention planning. Methods: We assessed patients from two stroke centers with 50-99% ICAD lesions. Using a novel technique, CTP scans generated acute vascular territory maps for major cerebral arteries (ACA,MCA,PCA) with perfusion Time-to-peak (TTP) maps. Patient-specific blood flow simulations using physiology-informed boundary conditions calculated stenotic pressure ratios for both the patient’s acute and a population-based healthy scenario. The changes in affected territory volumes and pressure ratio between healthy and acute conditions and the acute TTP delays were presented to an expert reader who stratified cases into three clinical groups (A) non-hemodynamic, (B) hemodynamically hazardous with insufficient collateral support and (C) hemodynamically stable due to collateralisation. These results were compared against patient outcomes of recurrent ischemic events attributed to the target stenosis using the commonly used 70% threshold. Results: (95%CI in brackets) Patients (n=47, age: 73±11Y, 23F/24M) were stratified across the three categories A) 30, B) 15, C) 2. Of the patient groups with follow-up (n=31), categorisation of hemodynamic ICAD against recurrent ipsilateral stroke in territory (n=8) yielded a sensitivity of 75% [34-97] and specificity of 91% [72-98]. Mean±standard deviation of stenosis degree (SD) 55±14% for patients across each cohort was A) 50±11%, B) 70±9%, C) 70%. This is compared to using 70% stenosis threshold for dichotomising patients against risk of recurrent stroke, which yielded a sensitivity of 62.5% [24-91], and specificity of 87% [66-97]. Conclusions: We report on a CTP derived method for stratifying hemodynamically significant ICAD. The methodology has potential in both in assessing symptomatic chronic ICAD and identifying cohorts who would benefit from endovascular intervention.

High Dose Rate and Fractionation to Reduce Radiation-Induced Lymphopenia: In Vivo Derivation of Lymphocyte Radiosensitivity Using Patient-Specific Blood Flow Simulations

<h3>Purpose/Objective(s)</h3> Radiation induced lymphopenia (RIL) has recently gained attention due to its correlation with outcome/survival in a range of indications, particularly when combining radiotherapy (RT) with immunotherapy. The purpose of this study is to use a dynamic blood circulation model combined with observed lymphocyte depletion in patients to derive the in vivo lymphocyte radiosensitivity and study the effect of fast delivery techniques. <h3>Materials/Methods</h3> We evaluated weekly Absolute Lymphocyte Counts (ALC) during RT and follow-up (median 7 measurements per patient) in 17 patients with hepatocellular carcinoma (HCC) treated with RT alone in 15 fractions (fx) using conventional dose rates. We utilized HEDOS, a time-dependent, whole-body, blood flow computational framework, in combination with explicit liver blood flow modeling, to calculate the dose volume histogram for circulating lymphocytes. We utilized linear-quadratic cell survival and an exponential recovery model optimized for lymphocyte radiation sensitivity, α (and β using α/β=2), and the daily recovery source term. We investigated the impact of using a 5-fx treatment regimen (currently investigated in a randomized trial – NCT03186898) and increasing the dose rate to delivery times <<1s (FLASH). The primary endpoints of interest were relative ALC depletion measured at nadir and time to recovery of 80% of baseline ALC. <h3>Results</h3> The <i>in-vivo</i> derived patient-specific lymphocyte radiation sensitivity has a mean of 0.7 <i>Gy⁻¹</i> (range 0.28 – 1.23) after optimal fitting using conventional fractionation and dose rate. Simulating a 5-fx treatment regimen at the conventional dose rate reduces ALC depletion by 8% on average, with an interquartile range (IQR) from 3% to 16% and mean reduction in number of days until recovery by 26% (IQR 21 – 31%) both caused by the varying patient-specific lymphocyte radiosensitivity. Simulating the 15-fx regimen with FLASH dose rates leads to a 13% reduction (IQR 3 – 23%) in ALC depletion and a mean reduction in number of days until recovery by 9% (IQR 2 – 116%). Combining the shorter, 5-fx, treatment regimen with FLASH dose rates leads to a mean reduction in ALC depletion by 45% (IQR 41 – 56%) and mean reduction in time to ALC recovery by 67% (IQR 54 – 80%). <h3>Conclusion</h3> We developed a patient-specific computational framework to simulate lymphocyte depletion in patients receiving RT depending on fractionation and dose rate. We observed that increasing dose rate at the same fractionation reduced ALC depletion more significantly than reducing the number of fractions. High dose rates led to an increased sparing of lymphocytes when shortening the fractionation regimen, particularly for patients with radiosensitive lymphocytes at elevated risk.

High-resolution cerebral blood flow simulation with a domain decomposition method and verified by the TCD measurement

Background: An efficient and accurate blood flow simulation can be useful for understanding many vascular diseases. Accurately resolving the blood flow velocity based on patient-specific geometries and model parameters is still a major challenge because of complex geomerty and turbulence issues. In addition, obtaining results in a short amount of computing time is important so that the simulation can be used in the clinical environment. In this work, we present a parallel scalable method for the patient-specific blood flow simulation with focuses on its parallel performance study and clinical verification.Methods: We adopt a fully implicit unstructured finite element method for a patient-specific simulation of blood flow in a full precerebral artery. The 3D artery is constructed from MRI images, and a parallel Newton–Krylov method preconditioned with a two-level domain decomposition method is adopted to solve the large nonlinear system discretized from the time-dependent 3D Navier-Stokes equations in the artery with an integral outlet boundary condition. The simulated results are verified using the clinical data measured by transcranial Doppler ultrasound, and the parallel performance of the algorithm is studied on a supercomputer.Results: The simulated velocity matches the clinical measured data well. Other simulated blood flow parameters, such as pressure and wall shear stress, are within reasonable ranges. The results show that the parallel algorithm scales up to 2160 processors with a 49% parallel efficiency for solving a problem with over 20 million unstructured elements on a supercomputer. For a standard cerebral blood flow simulation case with approximately 4 million finite elements, the calculation of one cardiac cycle can be finished within one hour with 1000 processors.Conclusion: The proposed method is able to perform high-resolution 3D blood flow simulations in a patient-specific full precerebral artery within an acceptable time, and the simulated results are comparable with the clinical measured data, which demonstrates its high potential for clinical applications.

Simulation of intracranial hemodynamics by an efficient and accurate immersed boundary scheme.

We use computational fluid dynamics (CFD) to simulate blood flow in intracranial aneurysms (IAs). Despite ongoing improvements in the accuracy and efficiency of body-fitted CFD solvers, generation of a high quality mesh appears as the bottleneck of the flow simulation and strongly affects the accuracy of the numerical solution. To overcome this drawback, we use an immersed boundary method. The proposed approach solves the incompressible Navier-Stokes equations on a rectangular (box) domain discretized using uniform Cartesian grid using the finite element method. The immersed object is represented by a set of points (Lagrangian points) located on the surface of the object. Grid local refinement is applied using an automated algorithm. We verify and validate the proposed method by comparing our numerical findings with published experimental results and analytical solutions. We demonstrate the applicability of the proposed scheme on patient-specific blood flow simulations in IAs.

Using Contrast Motion to Generate Patient-Specific Blood Flow Simulations During Invasive Coronary Angiography

Virtual fractional flow reserve (vFFR) is an emerging technology employing patient-specific computational fluid dynamics (CFD) simulations to infer the hemodynamic significance of a coronary stenosis. Patient-specific boundary conditions are an important aspect of this approach and while most efforts make use of lumped parameter models to capture key phenomena, they lack the ability to specify the associated parameters on a patient-specific basis. When applying vFFR in a catheter laboratory setting using X-ray angiograms as the basis for creating the simulations, there is some indirect functional information available through the observation of the radio-opaque contrast agent motion. In this work, we present a novel method for tuning the lumped parameter arterial resistances (commonly incorporated in such simulations), based on simulating the physics of the contrast motion and comparing the observed and simulated arrival times of the contrast front at key points within a coronary tree. We present proof of principle results on a synthetically generated coronary tree comprised of multiple segments, demonstrating that the method can successfully optimize the arterial resistances to reconstruct the underlying velocity and pressure fields, providing a potential new means to improve the patient specificity of simulation-based technologies in this area.

An Image-based Modeling Approach for Patient-Specific Blood Flow Simulations of Aortic Dissection

An Image-based Modeling Approach for Patient-Specific Blood Flow Simulations of Aortic Dissection

A simplified method to account for wall motion in patient-specific blood flow simulations of aortic dissection: Comparison with fluid-structure interaction

Aortic dissection (AD) is a complex and highly patient-specific vascular condition difficult to treat. Computational fluid dynamics (CFD) can aid the medical management of this pathology, yet its modelling and simulation are challenging. One aspect usually disregarded when modelling AD is the motion of the vessel wall, which has been shown to significantly impact simulation results. Fluid-structure interaction (FSI) methods are difficult to implement and are subject to assumptions regarding the mechanical properties of the vessel wall, which cannot be retrieved non-invasively. This paper presents a simplified ‘moving-boundary method’ (MBM) to account for the motion of the vessel wall in type-B AD CFD simulations, which can be tuned with non-invasive clinical images (e.g. 2D cine-MRI). The method is firstly validated against the 1D solution of flow through an elastic straight tube; it is then applied to a type-B AD case study and the results are compared to a state-of-the-art, full FSI simulation. Results show that the proposed method can capture the main effects due to the wall motion on the flow field: the average relative difference between flow and pressure waves obtained with the FSI and MBM simulations was less than 1.8% and 1.3%, respectively and the wall shear stress indices were found to have a similar distribution. Moreover, compared to FSI, MBM has the advantage to be less computationally expensive (requiring half of the time of an FSI simulation) and easier to implement, which are important requirements for clinical translation.

Blood Flow Simulation in Patient-Specific Segmented Hepatic Arterial Tree

PurposeSelective Internal Radiation Therapy is an emerging, minimally invasive therapy of liver cancer. Millions of microspheres are injected through a catheter into tumor vascular supply. Microspheres distribution in liver is strongly dependent on patient's arteries geometry and catheter tip positioning, which is currently chosen by the physician based on qualitative image interpretation. A patient-specific numerical simulation of blood flow would have a crucial importance in therapy optimization, allowing in-silico research of microspheres trajectories. Material and methodsWe developed a procedure to segment patient's hepatic arterial vasculature with a Hessian based approach on 3D angiography, and to perform blood flow numerical simulation in the extracted geometry with ANSYS Fluent. In vivo blood velocity measurements were performed using phase contrast MRI to constrain these simulations. ResultsFlow results in the larger vessels are coherent with literature, but very little is known for smaller arteries: simulation results are compared to velocity measures on hepatic arteries down to 2.2 mm of diameter on phase contrast MRI, which gave encouraging results for validation. ConclusionA viable procedure for arteries segmentation and patient-specific blood flow simulation is proposed, phase contrast MRI allowing for tuning and validation of velocity values. The proposed personalized blood flow simulation is compulsory for the simulation of microspheres trajectories in the aim of tumor targeting.

PC-MRI 計測データを用いたフィードバック制御データ同化手法に基づく患者個別脳動脈血流解析の計算的研究

PC-MRI 計測データを用いたフィードバック制御データ同化手法に基づく患者個別脳動脈血流解析の計算的研究

SimVascular: An Open Source Pipeline for Cardiovascular Simulation.

Patient-specific cardiovascular simulation has become a paradigm in cardiovascular research and is emerging as a powerful tool in basic, translational and clinical research. In this paper we discuss the recent development of a fully open-source SimVascular software package, which provides a complete pipeline from medical image data segmentation to patient-specific blood flow simulation and analysis. This package serves as a research tool for cardiovascular modeling and simulation, and has contributed to numerous advances in personalized medicine, surgical planning and medical device design. The SimVascular software has recently been refactored and expanded to enhance functionality, usability, efficiency and accuracy of image-based patient-specific modeling tools. Moreover, SimVascular previously required several licensed components that hindered new user adoption and code management and our recent developments have replaced these commercial components to create a fully open source pipeline. These developments foster advances in cardiovascular modeling research, increased collaboration, standardization of methods, and a growing developer community.

Investigation of blood flow in the external carotid artery and its branches with a new 0D peripheral model.

BackgroundPatient-specific modelling in clinical studies requires a realistic simulation to be performed within a reasonable computational time. The aim of this study was to develop simple but realistic outflow boundary conditions for patient-specific blood flow simulation which can be used to clarify the distribution of the anticancer agent in intra-arterial chemotherapy for oral cancer.MethodsIn this study, the boundary conditions are expressed as a zero dimension (0D) resistance model of the peripheral vessel network based on the fractal characteristics of branching arteries combined with knowledge of the circulatory system and the energy minimization principle. This resistance model was applied to four patient-specific blood flow simulations at the region where the common carotid artery bifurcates into the internal and external carotid arteries.ResultsResults of these simulations with the proposed boundary conditions were compared with the results of ultrasound measurements for the same patients. The pressure was found to be within the physiological range. The difference in velocity in the superficial temporal artery results in an error of 5.21 ± 0.78 % between the numerical results and the measurement data.ConclusionsThe proposed outflow boundary conditions, therefore, constitute a simple resistance-based model and can be used for performing accurate simulations with commercial fluid dynamics software.

Thrombotic risk stratification using computational modeling in patients with coronary artery aneurysms following Kawasaki disease.

Kawasaki disease (KD) is the leading cause of acquired heart disease in children and can result in life-threatening coronary artery aneurysms in up to 25% of patients. These aneurysms put patients at risk of thrombus formation, myocardial infarction, and sudden death. Clinicians must therefore decide which patients should be treated with anticoagulant medication, and/or surgical or percutaneous intervention. Current recommendations regarding initiation of anticoagulant therapy are based on anatomy alone with historical data suggesting that patients with aneurysms [Formula: see text]8mm are at greatest risk of thrombosis. Given the multitude of variables that influence thrombus formation, we postulated that hemodynamic data derived from patient-specific simulations would more accurately predict risk of thrombosis than maximum diameter alone. Patient-specific blood flow simulations were performed on five KD patients with aneurysms and one KD patient with normal coronary arteries. Key hemodynamic and geometric parameters, including wall shear stress, particle residence time, and shape indices, were extracted from the models and simulations and compared with clinical outcomes. Preliminary fluid structure interaction simulations with radial expansion were performed, revealing modest differences in wall shear stress compared to the rigid wall case. Simulations provide compelling evidence that hemodynamic parameters may be a more accurate predictor of thrombotic risk than aneurysm diameter alone and motivate the need for follow-up studies with a larger cohort. These results suggest that a clinical index incorporating hemodynamic information be used in the future to select patients for anticoagulant therapy.

Patient-specific Blood Flow Simulations: Setting Dirichlet Boundary Conditions for Minimal Error with Respect to Measured Data

We present a fully automatic approach to recover boundary conditions and locations of the vessel wall, given a crude initial guess and some velocity cross-sections, which can be corrupted by noise. This paper contributes to the body of work regarding patient-specific numerical simulations of blood flow, where the computational domain and boundary conditions have an implicit uncertainty and error, that derives from acquiring and processing clinical data in the form of medical images. The tools described in this paper fit well in the current approach of performing patient-specific simulations, where a reasonable segmentation of the medical images is used to form the computational domain, and boundary conditions are obtained as velocity cross-sections from phase-contrast magnetic resonance imaging. The only additional requirement in the proposed methods is to obtain additional velocity cross-section measurements throughout the domain. The tools developed around optimal control theory, would then minimize a user defined cost function to fit the observations, while solving the incompressible Navier-Stokes equations. Examples include two-dimensional idealized geometries and an anatomically realistic saccular geometry description.

The Vascular Model Repository: A Public Resource of Medical Imaging Data and Blood Flow Simulation Results.

Patient-specific blood flow simulations may provide insight into disease progression, treatment options, and medical device design that would be difficult or impossible to obtain experimentally. However, publicly available image data and computer models for researchers and device designers are extremely limited. The National Heart, Lung, and Blood Institute sponsored Open Source Medical Software Corporation (contract nos. HHSN268200800008C and HHSN268201100035C) and its university collaborators to build a repository (www.vascularmodel.org) including realistic, image-based anatomic models and related hemodynamic simulation results to address this unmet need.

A reconstruction platform for coronary arteries, finite element mesh generation and patient specific simulations

The left coronary artery (LCA) is one of the most important sites of atherosclerotic plaque formation and its progression may lead to stroke. There are many systemic risk factors that are related to the appearance and development of atherosclerosis. It has been observed, however, that the lesions occur in specific regions of the arterial tree. Nowadays it is accepted that these regions are the ones with low abnormal values of Wall Shear Stress (WSS). The aim of this work is to generate a platform to obtain a three-dimensional (3D) reconstruction from an LCA, generate a finite element mesh and run a patient specific blood flow simulation in it. The 3D model of the LCA reconstructed was based on a computed tomography (CT) study from a healthy patient. The method used for this procedure consisted basically on three stages: (1) segmenting the LCA principal branches from TC images, (2) extracting several contours from the arteries so as to get the essence of the geometry, applying a self-developed software, and (3) using this outlines to generate a Non-uniform rotational basis spline (NURBS surface). A finite element unstructured volume mesh was generated and refined and a simulation was run on it using a Computational Fluid Dynamics (CFD) application. The values of pressure and velocity were analyzed and WSS was computed. As expected, regions of low WSS were found in the outer walls of the bifurcation and in the inner wall of curvatures.

Patient-specific blood flow simulation through an aneurysmal thoracic aorta with a folded proximal neck

Transient blood flow through a geometrically patient-specific human aorta with a thoracic aortic aneurysm (TAA) is carried out. Special attention is given to the folded neck (kink) of the aneurysm found in the geometry studied. It is a common practice in the UK to intervene when the size of a TAA is between 5.5–6.5 cm. However, the results obtained suggest that neck or any other geometrical features of a TAA may also play a major role in determining the failure of an aortic aneurysm. Thus, we believe that the current practice of intervention needs to be reconsidered and a procedure based on flow classification and geometrical features may be required to minimize mortalities. To establish the effect of the kink, we have compared the results with and without the presence of the kink. The original geometry has been modified to obtain a geometry that is smoother without the kink. The results clearly show a drastic drop in wall shear stress when the kink is smoothed out. This clearly demonstrates that attention must be given to the shape and geometrical features of an aneurysm, in addition to its size. Copyright © 2010 John Wiley & Sons, Ltd.

Realistic and patient specific blood flow simulations

Realistic and patient specific blood flow simulations

Level set methods to build moving meshes for patient specific blood flow simulations

Introduction The hemodynamic factor in the thoracic aorta is believed to play an important role in the initiation and the progress of endovascular injuries. Most reported studies are dealing with averaged physiological geometries and rigid arterial boundaries. However, for diseases such as the aortic dissection, the geometrical changes are very patient specific and the wall motions over the cardiac cycle influence the blood flow drastically. There is a need to generalize the patient specific studies where the actual inlet/outlet boundary conditions and wall motions are accounted for. In the most general approach, the geometrical changes during the cardiac cycle result from the coupled fluid-structure interaction problem. This path is very challenging because the density of blood and tissues are of the same order, the rheology of the vessels is far from well understood and because the actual answer depends on the interaction of the arteries with the surrounding organs. Another option is to study the response of the blood flow submitted to prescribed wall motions and geometry changes. In this study we propose a method to build patient specific geometric data and boundary conditions for unsteady CFD runs with variable meshes valid over the cardiac cycle.