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International Journal for Numerical Methods in Biomedical Engineering

M Hirschvogel, M Bassilious, L Jagschies, S M Wildhirt, M W Gee
A model for patient-specific cardiac mechanics simulation is introduced, incorporating a 3-dimensional finite element model of the ventricular part of the heart which is coupled to a reduced-order 0-dimensional closed-loop vascular system, heart valve and atrial chamber model.The ventricles are modeled by a nonlinear orthotropic passive material law. The electrical activation is mimicked by a prescribed parametrized active stress acting along a generic muscle fiber orientation. Our activation function is constructed such that the start of ventricular contraction and relaxation as well as the active stress curve's slope are parameterized...
October 15, 2016: International Journal for Numerical Methods in Biomedical Engineering
Jason Carson, Raoul Van Loon
In this study the one dimensional blood flow equations are solved using a newly proposed enhanced trapezoidal rule method ETM, which is an extension to the simplified trapezoidal rule method STM. At vessel junctions the conservation of mass and conservation of total pressure are held as system constraints using Lagrange multipliers that can be physically interpreted as external flow rates. The ETM scheme is compared with published arterial network benchmark problems and a dam break problem. Strengths of the ETM scheme include being simple to implement, intuitive connection to lumped parameter models, and no restrictive stability criteria such as the CFL number...
October 6, 2016: International Journal for Numerical Methods in Biomedical Engineering
Ravishekar Ravi Kannan, Z J Chen, Narender Singh, Andrzej Przekwas, Renishkumar Delvadia, Geng Tian, Ross Walenga
The models used for modeling the airflow in the human airways are either 0D compartmental or full 3D Computational Fluid Dynamics (CFD) models. In the former, airways are treated as compartments and the computations are performed with several assumptions, thereby generating a low fidelity solution. The CFD method displays extremely high fidelity since the solution is obtained by solving the conservation equations in a physiologically consistent geometry. However, CFD models (i) require millions of degrees of freedom (DOF) to accurately describe the geometry and to reduce the discretization errors, (ii) have convergence problems and (iii) require several days to simulate a few breathing cycles...
October 5, 2016: International Journal for Numerical Methods in Biomedical Engineering
S Barone, A Paoli, A V Razionale, R Savignano
Transparent and removable aligners represent an effective solution to correct various orthodontic malocclusions through minimally invasive procedures. An aligner-based treatment requires patients to sequentially wear dentition-mating shells obtained by thermoforming polymeric disks on reference dental models. An aligner is shaped introducing a geometrical mismatch with respect to the actual tooth positions to induce a loading system, which moves the target teeth toward the correct positions. The common practice is based on selecting the aligner features (material, thickness, and auxiliary elements) by only considering clinician's subjective assessments...
October 5, 2016: International Journal for Numerical Methods in Biomedical Engineering
M O Khan, D A Steinman, K Valen-Sendstad
Computational fluid dynamics (CFD) shows promise for informing treatment planning and rupture risk assessment for intracranial aneurysms. Much attention has been paid to the impact on predicted hemodynamics of various modelling assumptions and uncertainties, including the need for modelling the non-Newtonian, shear-thinning rheology of blood, with equivocal results. Our study clarifies this issue by contextualizing the impact of rheology model against the recently-demonstrated impact of CFD solution strategy on the prediction of aneurysm flow instabilities...
October 1, 2016: International Journal for Numerical Methods in Biomedical Engineering
M Lange, S Palamara, T Lassila, C Vergara, A Quarteroni, A F Frangi
Cardiac Purkinje fibres provide an important pathway to the coordinated contraction of the heart. We present a numerical algorithm for the solution of electrophysiology problems across the Purkinje network that is efficient enough to be used in in-silico studies on realistic Purkinje networks with physiologically detailed models of ion exchange at the cell membrane. The algorithm is based on operator splitting and is provided with three different implementations: pure CPU, hybrid CPU/GPU, and pure GPU. Compared to our previous work, we modify the explicit gap junction term at network bifurcations in order to improve its mathematical consistency...
September 23, 2016: International Journal for Numerical Methods in Biomedical Engineering
Yansheng Jiang, Ricardo Possebon, Stefaan Mulier, Chong Wang, Feng Chen, Yuanbo Feng, Qian Xia, Yewei Liu, Ting Yin, Raymond Oyen, Yicheng Ni
Radiofrequency ablation (RFA) is a minimally invasive thermal therapy for the treatment of cancer, hyperopia, and cardiac tachyarrhythmia. In RFA, the power delivered to the tissue is a key parameter. The objective of this study was to establish a methodology for the finite element modeling of RFA with constant power. Because of changes in the electric conductivity of tissue with temperature, a nonconventional boundary value problem arises in the mathematic modeling of RFA: neither the voltage (Dirichlet condition) nor the current (Neumann condition), but the power, that is, the product of voltage and current was prescribed on part of boundary...
September 21, 2016: International Journal for Numerical Methods in Biomedical Engineering
Silvia Oviedo, Josep Vehí, Remei Calm, Joaquim Armengol
This paper presents a methodological review of models for predicting blood glucose (BG) concentration, risks and BG events. The surveyed models are classified into three categories, and they are presented in summary tables containing the most relevant data regarding the experimental setup for fitting and testing each model as well as the input signals and the performance metrics. Each category exhibits trends that are presented and discussed. This document aims to be a compact guide to determine the modeling options that are currently being exploited for personalized BG prediction...
September 19, 2016: International Journal for Numerical Methods in Biomedical Engineering
Ahnryul Choi, David D McPherson, Hyunggun Kim
Mitral regurgitation (MR) is a result of mitral valve (MV) pathology. Its etiology can be categorized as degenerative or functional MR. Ring annuloplasty aims to reconfigure a dilated mitral annulus to its normal size and shape. We investigated the effect of annuloplasty ring shape on MR outcome using our established 3-dimensional (3-D) echocardiography-based computational MV evaluation protocols. Virtual patient MV models were created from 3-D transesophageal echocardiographic data in patients with MR because of mitral annular dilation...
September 7, 2016: International Journal for Numerical Methods in Biomedical Engineering
Ana F Tena, Joaquín Fernández, Eduardo Álvarez, Pere Casan, D Keith Walters
BACKGROUND: The need for a better understanding of pulmonary diseases has led to increased interest in the development of realistic computational models of the human lung. METHODS: To minimize computational cost, a reduced geometry model is used for a model lung airway geometry up to generation 16. Truncated airway branches require physiologically realistic boundary conditions to accurately represent the effect of the removed airway sections. A user-defined function has been developed, which applies velocities mapped from similar locations in fully resolved airway sections...
September 5, 2016: International Journal for Numerical Methods in Biomedical Engineering
Hossein Mohammadi, Raymond Cartier, Rosaire Mongrain
The diseases of the coronary arteries and the aortic root are still the leading causes of mortality and morbidity worldwide. In this study, a 3D global fluid-structure interaction of the aortic root with inclusion of anatomically inspired small coronary arteries using the finite element method is presented. This innovative model allows to study the impact and interaction of root biomechanics on coronary hemodynamics and brings a new understanding to small coronary vessels hemodynamics. For the first time, the velocity profiles and shear stresses are reported in distal coronary arteries as a result of the aortic flow conditions in a global fluid-structure interaction model...
September 3, 2016: International Journal for Numerical Methods in Biomedical Engineering
P Di Achille, G Tellides, J D Humphrey
Accumulating evidence suggests that intraluminal thrombus plays many roles in the natural history of abdominal aortic aneurysms. There is, therefore, a pressing need for computational models that can describe and predict the initiation and progression of thrombus in aneurysms. In this paper, we introduce a phenomenological metric for thrombus deposition potential and use hemodynamic simulations based on medical images from 6 patients to identify best-fit values of the 2 key model parameters. We then introduce a shape optimization method to predict the associated radial growth of the thrombus into the lumen based on the expectation that thrombus initiation will create a thrombogenic surface, which in turn will promote growth until increasing hemodynamically induced frictional forces prevent any further cell or protein deposition...
August 29, 2016: International Journal for Numerical Methods in Biomedical Engineering
Liang Liang, Fanwei Kong, Caitlin Martin, Thuy Pham, Qian Wang, James Duncan, Wei Sun
To conduct a patient-specific computational modeling of the aortic valve, 3-D aortic valve anatomic geometries of an individual patient need to be reconstructed from clinical 3-D cardiac images. Currently, most of computational studies involve manual heart valve geometry reconstruction and manual finite element (FE) model generation, which is both time-consuming and prone to human errors. A seamless computational modeling framework, which can automate this process based on machine learning algorithms, is desirable, as it can not only eliminate human errors and ensure the consistency of the modeling results but also allow fast feedback to clinicians and permits a future population-based probabilistic analysis of large patient cohorts...
August 24, 2016: International Journal for Numerical Methods in Biomedical Engineering
Yung-Chang Cheng, Deng-Huei Lin, Cho-Pei Jiang, Yuan-Min Lin
This study proposes a new methodology for dental implant customization consisting of numerical geometric optimization and three-dimensional printing fabrication of zirconia ceramic. In the numerical modeling, exogenous factors for implant shape include the thread pitch, thread depth, maximal diameter of implant neck and body size. Endogenous factors are bone density, cortical bone thickness and non-osseointegration. An integration procedure, including uniform design method, kriging interpolation and genetic algorithm (KIGA), is applied to optimize the geometry of dental implants...
August 18, 2016: International Journal for Numerical Methods in Biomedical Engineering
H Fujii, Y Yamada, K Kobayashi, M Watanabe, Y Hoshi
Diffuse optical tomography (DOT) using near-infrared light in a wavelength range from 700 nm to 1000 nm has the potential to enable non-invasive diagnoses of thyroid cancers, some of which are difficult to detect by conventional methods such as ultrasound tomography. DOT needs to be based on a physically accurate model of light propagation in the neck, because it reconstructs tomographic images of the optical properties in the human neck by inverse analysis. Our objective here was to investigate the effects of three factors on light propagation in the neck using the 2D time-dependent radiative transfer equation: (i) the presence of the trachea, (ii) the refractive-index mismatch at the trachea-tissue interface, and (iii) the effect of neck organs other than the trachea (spine, spinal cord, and blood vessels)...
August 17, 2016: International Journal for Numerical Methods in Biomedical Engineering
Rajnesh Lal, Bijan Mohammadi, Franck Nicoud
A method to estimate the hemodynamics parameters of a network of vessels using an Ensemble Kalman filter is presented. The elastic moduli (Young's modulus) of blood vessels and the terminal boundary parameters are estimated as the solution of an inverse problem. Two synthetic test cases and a configuration where experimental data is available are presented. The sensitivity analysis confirms that the proposed method is quite robust even with a few numbers of observations. The simulations with the estimated parameters recovers target pressure or flow rate waveforms at given specific locations, improving the state of the art predictions available in the literature...
August 17, 2016: International Journal for Numerical Methods in Biomedical Engineering
Azadeh A T Borojeni, Dennis O Frank-Ito, Julia S Kimbell, John S Rhee, Guilherme J M Garcia
Virtual surgery planning based on computational fluid dynamics (CFD) simulations has the potential to improve surgical outcomes for nasal airway obstruction (NAO) patients, but the benefits of virtual surgery planning must outweigh the risks of radiation exposure. Cone beam computed tomography (CBCT) scans represent an attractive imaging modality for virtual surgery planning due to lower costs and lower radiation exposures compared with conventional CT scans. However, to minimize the radiation exposure, the CBCT sinusitis protocol sometimes images only the nasal cavity, excluding the nasopharynx...
August 15, 2016: International Journal for Numerical Methods in Biomedical Engineering
Lachlan J Kelsey, Janet T Powell, Paul E Norman, Karol Miller, Barry J Doyle
Aneurysms of the common iliac artery (CIAA) are most commonly seen in association with an abdominal aortic aneurysm (AAA). Isolated CIAAs, in the absence of an AAA, are uncommon. Similar to AAAs, CIAA may develop intraluminal thrombus (ILT). As isolated CIAAs have a contralateral common iliac artery for comparison, they provide an opportunity to study the haemodynamic mechanisms behind ILT formation. In this study, we compared a large isolated CIAA and the contralateral iliac artery using computational fluid dynamics (CFD) to determine if haemodynamic metrics correlate with the location of ILT...
August 10, 2016: International Journal for Numerical Methods in Biomedical Engineering
Josep M López, Gerard Fortuny, Dolors Puigjaner, Joan Herrero, Francesc Marimon, Josep Garcia-Bennett
Deep venous thrombosis (DVT) is a common disease. Large thrombi in venous vessels cause bad blood circulation and pain; and when a blood clot detaches from a vein wall, it causes an embolism whose consequences range from mild to fatal. Walking is recommended to DVT patients as a therapeutical complement. In this study the mechanical effects of walking on a specific patient of DVT were simulated by means of an unprecedented integration of three elements: a real geometry, a biomechanical model of body tissues and a computational fluid dynamics (CFD) study...
August 9, 2016: International Journal for Numerical Methods in Biomedical Engineering
Harsha T Garimella, Reuben H Kraft
A subject-speciVc human head Vnite element model with embedded axonal Vber tractography obtained from diUusion tensor imaging was developed. The axonal Vber tractography Vnite element model was coupled with the volumetric elements in the head model using the embedded element method. This technique enables the calculation of axonal strains and real-time tracking of the mechanical response of the axonal Vber tracts. The coupled model was then veriVed using pressure and relative displacement-based (between skull and brain) experimental studies and was employed to analyze a head impact, demonstrating the applicability of this method in studying axonal injury...
August 8, 2016: International Journal for Numerical Methods in Biomedical Engineering
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