Cyclic Breathing Simulations: Pressure Outlet Boundary Conditions Coupled With Resistance and Compliance

A patient-specific non-uniform pressure outlet boundary condition was developed and used in unsteady simulations of cyclic breathing in a large-scale model of the lung airway from the oronasal opening to the terminal bronchioles. The computational domain is a reduced-geometry model, in which some airway branches in each generation were truncated, and only selected paths were retained to the terminal generation. To characterize pressure change through airway tree extending from the truncated outlets to pulmonary zone, virtual airways represented by extended volume mesh zones were constructed in order to apply a zero-dimensional airway resistance model. The airway resistances were prescribed based on a precursor steady simulation under constant ventilation condition. The virtual airways accommodate the use of patient-specific alveolar pressure conditions. Furthermore, the time-dependent alveolar pressure profile was composed with the physiologically accurate pleural pressure predicted by the whole-body simulation software HumMod, and the transpulmonary pressure evaluated based on lung compliance and local air volume change. To investigate airway flow patterns of healthy and diseased lungs, unsteady breathing simulations were conducted with varying lung compliances accounting for healthy lungs, and lungs with emphysema or interstitial fibrosis. Results show that the simulations using this patient-specific pressure boundary condition are capable of reproducing physiologically realistic flow patterns corresponding to abnormal pulmonary compliance in diseased lungs, such as the hyperventilation in lungs with emphysema, and the demand of more mechanic work for breathing in lungs with fibrosis.

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Cyclic Breathing Simulations in Large-Scale Models of the Lung Airway From the Oronasal Opening to the Terminal Bronchioles

Journal of Fluids Engineering ◽

10.1115/1.4027485 ◽

2014 ◽

Vol 136 (10) ◽

Cited By ~ 3

Author(s):

D. Keith Walters ◽

Greg W. Burgreen ◽

Robert L. Hester ◽

David S. Thompson ◽

David M. Lavallee ◽

...

Keyword(s):

Boundary Conditions ◽

Mass Flow ◽

Flow Rate ◽

Large Scale ◽

Whole Body ◽

Patient Specific ◽

Computational Domain ◽

Scale Models ◽

Fully Coupled ◽

Conducting Zone

Computational fluid dynamics (CFD) simulations were performed using large-scale models of the human lung airway and unsteady periodic breathing conditions. The computational domain included fully coupled representations of the orotracheal region and large conducting zone up to generation four (G4) obtained from patient-specific CT data, and the small conducting zone (to the 16th generation) obtained from a stochastically generated airway tree with statistically realistic morphological characteristics. A reduced-geometry airway model was used, in which several airway branches in each generation were truncated, and only select flow paths were retained to the 16th generation. The inlet and outlet flow boundaries corresponded to the oral opening, the physical inlet/outlet boundaries at the terminal bronchioles, and the unresolved airway boundaries created from the truncation procedure. The total flow rate was specified according to the expected ventilation pattern for a healthy adult male, which was supplied by the whole-body modeling software HumMod. The unsteady mass flow distribution at the distal boundaries was prescribed based on a preliminary steady-state simulation with an applied flow rate equal to the average flow rate during the inhalation phase of the breathing cycle. In contrast to existing studies, this approach allows fully coupled simulation of the entire conducting zone, with no need to specify distal mass flow or pressure boundary conditions a priori, and without the use of impedance or one-dimensional (1D) flow models downstream of the truncated boundaries. The results show that: (1) physiologically realistic flow is obtained in the model, in terms of cyclic mass conservation and approximately uniform pressure distribution in the distal airways; (2) the predicted alveolar pressure is in good agreement with correlated experimental data; and (3) the use of reduced-order geometry modeling allows accurate and efficient simulation of large-scale breathing lung flow, provided care is taken to use a physiologically realistic geometry and to properly address the unsteady boundary conditions.

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Accurate Simulation of Light Propagation in Complex Skin Tissues Using an Improved Tetrahedron-Based Monte Carlo Method

Applied Sciences ◽

10.3390/app11072998 ◽

2021 ◽

Vol 11 (7) ◽

pp. 2998

Author(s):

Hao Jia ◽

Bin Chen ◽

Dong Li

Keyword(s):

Boundary Condition ◽

Monte Carlo ◽

Energy Deposition ◽

Laser Energy ◽

Patient Specific ◽

Computational Domain ◽

Photon Propagation ◽

Cross Bridge ◽

Diffused Light ◽

Mc Method

Understanding light transportation in skin tissues can help improve clinical efficacy in the laser treatment of dermatosis, such as port-wine stains (PWS). Patient-specific cross-bridge PWS vessels are structurally complicated and considerably influence laser energy deposition due to shading effects. The shading effect of PWS vessels is investigated using a tetrahedron-based Monte Carlo (MC) method with extended boundary condition (TMCE). In TMCE, body-fitted tetrahedra are generated in different tissues, and the precision of photon–surface interaction can be considerably improved via mesh refinement. Such improvement is difficult to achieve with the widely used voxel-based MC method. To fit the real physical boundary, the extended boundary condition is adapted by extending photon propagation to the semi-infinite tissue layers while restricting the statistics of photon propagation in the computational domain. Results indicate that the shading parameters, such as the cross angle, vessel distance, and geometric shadow (GS), of cross-bridge blood vessel pairs determine the peak characteristics of photon deposition in deep vessels by affecting the relative deposition of collimated and diffused light. Collimated light is shaded, attenuated, and partially transformed into diffused light due to the increase in vessel distance and GS of vessel pairs, resulting in difficulty in treating deep and shallow vessels with one laser pulse. The TMCE method can be used for the individualized and precise forecasting of laser energy deposition based on the morphology and embedding characteristics of vascular lesions.

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A Numerical Analysis of the Hemodynamic Functionality of Human Coronary Stenosis Under Different Physiologic Conditions and Boundary Condition Formulations

Volume 2: Computational Fluid Dynamics ◽

10.1115/ajkfluids2019-4820 ◽

2019 ◽

Author(s):

Iyad Fayssal ◽

Fadl Moukalled

Keyword(s):

Boundary Condition ◽

Boundary Conditions ◽

Functional Significance ◽

Diffusion Flux ◽

Computational Effort ◽

Patient Specific ◽

Computational Domain ◽

Artery Disease ◽

Outflow Boundary

Abstract Coronary artery disease (CAD) is among the foremost causes for human death worldwide. This study aims at investigating the performance of different boundary condition model types to characterize CAD functional significance. In addition, alternate models to estimate FFR using any different combination of boundary conditions at inlet and outlet were analyzed. In the first type of boundary condition, an outflow resistance model is used combined with a fixed pressure at inlet. In the second model of boundary conditions, constant pressure values are imposed at the domain inlet and outlet/s sections. In the third model, a zero diffusion flux is applied at outlet with a pre-specified flow rate at inlet. Numerical simulations performed on healthy and stenosed idealized and physiological arterial models revealed the superiority of the first type of boundary condition to directly capture the level of ischemia in diseased arteries. However, in this model, special numerical treatment at the outflow boundary is needed to dampen pseudo numerical reflections entering the computational domain. Alternative simple methods are developed to tackle the problem incurred in the second and third types of boundary condition types. The alternate models are effective for carrying extensive parametric studies with minimal computational effort. The new developed methods allow results generated via generic simulations under any specified boundary condition type to correctly estimate CAD functional significance. The obtained surrogate models account for the effects of the patient-specific physiologic parameters and can be easily incorporated without modifying existing CFD codes. Moreover, where it is unfeasible to experimentally incorporate the downstream effects of a given diseased arterial segment, an important aspect the alternative models provide is that they can be easily adopted by experimentalists through building in-vitro arterial models to assess the functional significance of the obstruction caused by the disease and its relation to any given patient specific physiologic parameter.

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Usefulness of the patient-specific contrast enhancement optimizer simulation software during the whole-body computed tomography angiography

Heart and Vessels ◽

10.1007/s00380-022-02024-z ◽

2022 ◽

Author(s):

Takanori Masuda ◽

Toru Higaki ◽

Takeshi Nakaura ◽

Yoshinori Funama ◽

Yoriaki Matsumoto ◽

...

Keyword(s):

Computed Tomography ◽

Contrast Enhancement ◽

Computed Tomography Angiography ◽

Simulation Software ◽

Whole Body ◽

Patient Specific ◽

Whole Body Computed Tomography

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Incorporating Patient-Specific Variability in the Simulation of Realistic Whole-Body $^{18}{\hbox{F-FDG}}$ Distributions for Oncology Applications

Proceedings of the IEEE ◽

10.1109/jproc.2009.2027925 ◽

2009 ◽

Vol 97 (12) ◽

pp. 2026-2038 ◽

Cited By ~ 42

Author(s):

Amandine Le Maitre ◽

William Paul Segars ◽

Simon Marache ◽

Anthonin Reilhac ◽

Mathieu Hatt ◽

...

Keyword(s):

Whole Body ◽

Patient Specific

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Fully Coupled Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel with a 0.1 Blockage Ratio

Energies ◽

10.3390/en14082096 ◽

2021 ◽

Vol 14 (8) ◽

pp. 2096

Author(s):

Joon Ahn ◽

Jeong Chul Song ◽

Joon Sik Lee

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Conjugate Heat Transfer ◽

Heat Transfer Analysis ◽

Scale Model ◽

Computational Domain ◽

Blockage Ratio ◽

Ribbed Channel ◽

Large Eddy ◽

Cooling Passage

Large eddy simulations are performed to analyze the conjugate heat transfer of turbulent flow in a ribbed channel with a heat-conducting solid wall. An immersed boundary method (IBM) is used to determine the effect of heat transfer in the solid region on that in the fluid region in a unitary computational domain. To satisfy the continuity of the heat flux at the solid–fluid interface, effective conductivity is introduced. By applying the IBM, it is possible to fully couple the convection on the fluid side and the conduction inside the solid and use a dynamic subgrid scale model in a Cartesian grid. The blockage ratio (e/H) is set at 0.1, which is typical for gas turbine blades. Through conjugate heat transfer analysis, it is confirmed that the heat transfer peak in front of the rib occurs because of the impinging of the reattached flow and not the influence of the thermal boundary condition. When the rib turbulator acts as a fin, its efficiency and effectiveness are predicted to be 98.9% and 8.32, respectively. When considering conjugate heat transfer, the total heat transfer rate is reduced by 3% compared with that of the isothermal wall. The typical Biot number at the internal cooling passage of a gas turbine is <0.1, and the use of the rib height as the characteristic length better represents the heat transfer of the rib.

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A method for evaluation of patient-specific lean body mass from limited-coverage CT images and its application in PERCIST: comparison with predictive equation

EJNMMI Physics ◽

10.1186/s40658-021-00358-7 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Jingjie Shang ◽

Zhiqiang Tan ◽

Yong Cheng ◽

Yongjin Tang ◽

Bin Guo ◽

...

Keyword(s):

Lean Body Mass ◽

Body Mass ◽

Whole Body ◽

Patient Specific ◽

Predictive Equation ◽

Reference Standard ◽

Pet Ct ◽

Before And After ◽

Percist 1.0 ◽

Limited Coverage

Abstract Background Standardized uptake value (SUV) normalized by lean body mass ([LBM] SUL) is recommended as metric by PERCIST 1.0. The James predictive equation (PE) is a frequently used formula for LBM estimation, but may cause substantial error for an individual. The purpose of this study was to introduce a novel and reliable method for estimating LBM by limited-coverage (LC) CT images from PET/CT examinations and test its validity, then to analyse whether SUV normalised by LC-based LBM could change the PERCIST 1.0 response classifications, based on LBM estimated by the James PE. Methods First, 199 patients who received whole-body PET/CT examinations were retrospectively retrieved. A patient-specific LBM equation was developed based on the relationship between LC fat volumes (FVLC) and whole-body fat mass (FMWB). This equation was cross-validated with an independent sample of 97 patients who also received whole-body PET/CT examinations. Its results were compared with the measurement of LBM from whole-body CT (reference standard) and the results of the James PE. Then, 241 patients with solid tumours who underwent PET/CT examinations before and after treatment were retrospectively retrieved. The treatment responses were evaluated according to the PE-based and LC-based PERCIST 1.0. Concordance between them was assessed using Cohen’s κ coefficient and Wilcoxon’s signed-ranks test. The impact of differing LBM algorithms on PERCIST 1.0 classification was evaluated. Results The FVLC were significantly correlated with the FMWB (r=0.977). Furthermore, the results of LBM measurement evaluated with LC images were much closer to the reference standard than those obtained by the James PE. The PE-based and LC-based PERCIST 1.0 classifications were discordant in 27 patients (11.2%; κ = 0.823, P=0.837). These discordant patients’ percentage changes of peak SUL (SULpeak) were all in the interval above or below 10% from the threshold (±30%), accounting for 43.5% (27/62) of total patients in this region. The degree of variability is related to changes in LBM before and after treatment. Conclusions LBM algorithm-dependent variability in PERCIST 1.0 classification is a notable issue. SUV normalised by LC-based LBM could change PERCIST 1.0 response classifications based on LBM estimated by the James PE, especially for patients with a percentage variation of SULpeak close to the threshold.

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Cyclic Breathing Simulations in Large Scale Models of the Lung Airway From the Oronasal Opening to the Terminal Bronchioles

Volume 2: Biomedical and Biotechnology ◽

10.1115/imece2012-88901 ◽

2012 ◽

Author(s):

D. Keith Walters ◽

Greg W. Burgreen ◽

Robert L. Hester ◽

David S. Thompson ◽

David M. Lavallee ◽

...

Keyword(s):

Steady State ◽

Boundary Conditions ◽

Large Scale ◽

Whole Body ◽

Patient Specific ◽

Cfd Simulations ◽

Reduced Order ◽

Scale Models ◽

Steady State Simulation ◽

Conducting Zone

Computational fluid dynamics (CFD) simulations were performed for unsteady periodic breathing conditions, using large-scale models of the human lung airway. The computational domain included fully coupled representations of the orotracheal region and large conducting zone up to generation four (G4) obtained from patient-specific CT data, and the small conducting zone (to G16) obtained from a stochastically generated airway tree with statistically realistic geometrical characteristics. A reduced-order geometry was used, in which several airway branches in each generation were truncated, and only select flow paths were retained to G16. The inlet and outlet flow boundaries corresponded to the oronasal opening (superior), the inlet/outlet planes in terminal bronchioles (distal), and the unresolved airway boundaries arising from the truncation procedure (intermediate). The cyclic flow was specified according to the predicted ventilation patterns for a healthy adult male at three different activity levels, supplied by the whole-body modeling software HumMod. The CFD simulations were performed using Ansys FLUENT. The mass flow distribution at the distal boundaries was prescribed using a previously documented methodology, in which the percentage of the total flow for each boundary was first determined from a steady-state simulation with an applied flow rate equal to the average during the inhalation phase of the breathing cycle. The distal pressure boundary conditions for the steady-state simulation were set using a stochastic coupling procedure to ensure physiologically realistic flow conditions. The results show that: 1) physiologically realistic flow is obtained in the model, in terms of cyclic mass conservation and approximately uniform pressure distribution in the distal airways; 2) the predicted alveolar pressure is in good agreement with previously documented values; and 3) the use of reduced-order geometry modeling allows accurate and efficient simulation of large-scale breathing lung flow, provided care is taken to use a physiologically realistic geometry and to properly address the unsteady boundary conditions.

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Hybrid Spine Simulator Prototype for X-ray Free Pedicle Screws Fixation Training

Applied Sciences ◽

10.3390/app11031038 ◽

2021 ◽

Vol 11 (3) ◽

pp. 1038

Author(s):

Sara Condino ◽

Giuseppe Turini ◽

Virginia Mamone ◽

Paolo Domenico Parchi ◽

Vincenzo Ferrari

Keyword(s):

Augmented Reality ◽

Low Cost ◽

Lumbar Vertebrae ◽

Pedicle Screws ◽

Simulation Software ◽

Patient Specific ◽

Innovative Strategy ◽

X Ray ◽

3D Printed ◽

Harmful Radiation

Simulation for surgical training is increasingly being considered a valuable addition to traditional teaching methods. 3D-printed physical simulators can be used for preoperative planning and rehearsal in spine surgery to improve surgical workflows and postoperative patient outcomes. This paper proposes an innovative strategy to build a hybrid simulation platform for training of pedicle screws fixation: the proposed method combines 3D-printed patient-specific spine models with augmented reality functionalities and virtual X-ray visualization, thus avoiding any exposure to harmful radiation during the simulation. Software functionalities are implemented by using a low-cost tracking strategy based on fiducial marker detection. Quantitative tests demonstrate the accuracy of the method to track the vertebral model and surgical tools, and to coherently visualize them in either the augmented reality or virtual fluoroscopic modalities. The obtained results encourage further research and clinical validation towards the use of the simulator as an effective tool for training in pedicle screws insertion in lumbar vertebrae.

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