Semiautomated Skeletonization of the Pulmonary Arterial Tree in Micro-CT Images

We present a simple and robust approach that utilizes planar images at different angular rotations combined with unfiltered back-projection to locate the central axes of the pulmonary arterial tree. Three-dimensional points are selected interactively by the user. The computer calculates a sub- volume unfiltered back-projection orthogonal to the vector connecting the two points and centered on the first point. Because more x-rays are absorbed at the thickest portion of the vessel, in the unfiltered back-projection, the darkest pixel is assumed to be the center of the vessel. The computer replaces this point with the newly computer-calculated point. A second back-projection is calculated around the original point orthogonal to a vector connecting the newly-calculated first point and user-determined second point. The darkest pixel within the reconstruction is determined. The computer then replaces the second point with the XYZ coordinates of the darkest pixel within this second reconstruction. Following a vector based on a moving average of previously determined 3- dimensional points along the vessel\u27s axis, the computer continues this skeletonization process until stopped by the user. The computer estimates the vessel diameter along the set of previously determined points using a method similar to the full width-half max algorithm. On all subsequent vessels, the process works the same way except that at each point, distances between the current point and all previously determined points along different vessels are determined. If the difference is less than the previously estimated diameter, the vessels are assumed to branch. This user/computer interaction continues until the vascular tree has been skeletonized

Biomedical and biophysical limits to mathematical modeling of pulmonary system mechanics: a scoping review on aerosol and drug delivery.

Undoubtedly, the construction of the biomechanical geometry systems with the help of computer tomography (CT) and magnetic resonance imaging (MRI) has made a significant advancement in studying in vitro numerical models as accurately as possible. However, some simplifying assumptions in the computational studies of the respiratory system have caused errors and deviations from the in vivo actual state. The most important of these hypotheses is how to generate volume from the point cloud exported from CT or MRI images, not paying attention to the wall thickness and its effect in computational fluid dynamic method, statistical logic of aerosol trap in software; and most importantly, the viscoelastic effect of respiratory tract wall in living tissue pointed in the fluid-structure interaction method. So that applying the viscoelastic dynamic mesh effect in the form of the moving deforming mesh can be very effective in achieving more appropriate response quality. Also, changing the volume fraction of the pulmonary extracellular matrix constituents leads to changes in elastic modulus (storage modulus) and the viscous modulus (loss modulus) of lung tissue. Therefore, in the biomedical computational methods where the model wall is considered flexible, the viscoelastic properties of the texture must be considered correctly

Effect of upper airway on tracheobronchial fluid dynamics

The upper airways play a significant role in the tracheal flow dynamics. Despite many previous studies, however, the effect of the upper airways on the ventilation distribution in distal airways has remained a challenge. The aim of this study is to experimentally and computationally investigate the dynamic behaviour in the intratracheal flow induced by the upper respiratory tract and to assess its influence on the subsequent tributaries. Patient-specific images from 2 different modalities (magnetic resonance imaging of the upper airways and computed tomography of the lower airways) were segmented and combined. An experimental phantom of patient-specific airways (including the oral cavity, larynx, trachea, down to generations 6-8) was generated using 3D printing. The flow velocities in this phantom model were measured by the flow-sensitised phase contrast magnetic resonance imaging technique and compared with the computational fluid dynamics simulations. Both experimental and computational results show a good agreement in the time-averaged velocity fields as well as fluctuating velocity. The flows in the proximal trachea were complex and unsteady under both lower- and higher-flow rate conditions. Computational fluid dynamics simulations were also performed with an airways model without the upper airways. Although the flow near the carina remained unstable only when the inflow rate was high, the influence of the upper airways caused notable changes in distal flow distributions when the 2 airways models were compared with and without the upper airways. The results suggest that the influence of the upper airways should be included in the respiratory flow assessment as the upper airways extensively affect the flows in distal airways and consequent ventilation distribution in the lungs

Fluid-structure interaction in lower airways of CT-based lung geometries

In this study, the deformability of airway walls is taken into account to study airflow patterns and airway wall stresses in the first generations of lower airways in a real lung geometry. The lung geometry is based on CT-scans that are obtained from in-vivo experiments on humans. A partitioned fluid-structure interaction (FSI) approach, realized within a parallel in-house finite element code, is employed. It is designed for the robust and eficient simulation of the interaction of transient incompressible Newtonian flows and (geometrically) nonlinear airway wall behavior. Arbitrary Lagrangian Eulerian (ALE)-based stabilized tetrahedral finite elements are used for the fluid and Lagrangian-based 7-parametric mixed/hybrid shell elements are used for the airway walls using unstructured meshes due to the complexity of the geometry. Air flow patterns as well as airway wall stresses in the bronchial tree are studied for a number of different scenarios. Thereby, both models for healthy and diseased lungs are taken into account and both normal breathing and mechanical ventilation scenarios are studied

Optimización fluido-dinámica de un stent de tráquea

Estudio por elementos finitos y CFD de un stent de tráquea con diferentes modificaciones con el objetivo de lograr la optimización del flujo de aire circulante

Biomechanical Models of Human Upper and Tracheal Airway Functionality

The respiratory tract, in other words, the airway, is the primary airflow path for several physiological activities such as coughing, breathing, and sneezing. Diseases can impact airway functionality through various means including cancer of the head and neck, Neurological disorders such as Parkinson\u27s disease, and sleep disorders and all of which are considered in this study. In this dissertation, numerical modeling techniques were used to simulate three distinct airway diseases: a weak cough leading to aspiration, upper airway patency in obstructive sleep apnea, and tongue cancer in swallow disorders. The work described in this dissertation, therefore, divided into three biomechanical models, of which fluid and particulate dynamics model of cough is the first. Cough is an airway protective mechanism, which results from a coordinated series of respiratory, laryngeal, and pharyngeal muscle activity. Patients with diminished upper airway protection often exhibit cough impairment resulting in aspiration pneumonia. Computational Fluid Dynamics (CFD) technique was used to simulate airflow and penetrant behavior in the airway geometry reconstructed from Computed Tomography (CT) images acquired from participants. The second study describes Obstructive Sleep Apnea (OSA) and the effects of dilator muscular activation on the human retro-lingual airway in OSA. Computations were performed for the inspiration stage of the breathing cycle, utilizing a fluid-structure interaction (FSI) method to couple structural deformation with airflow dynamics. The spatiotemporal deformation of the structures surrounding the airway wall was predicted and found to be in general agreement with observed changes in luminal opening and the distribution of airflow from upright to supine posture. The third study describes the effects of cancer of the tongue base on tongue motion during swallow. A three-dimensional biomechanical model was developed and used to calculate the spatiotemporal deformation of the tongue under a sequence of movements which simulate the oral stage of swallow

Numerical modelling of airflow dynamics and particle deposition in human lungs

Research into airflow dynamics and particle transport in human lungs is receiving considerable attention from many researchers because of its significance for human health. Drug delivery through inhalation of air into the human lung is important to prevent/cure respiratory diseases. Many researchers have investigated the process of particle transport and deposition (TD) in the respiratory airway through analytical as well as numerical methods, during the last century. Nowadays, numerical methods are used to model various biomechanical engineering problems, including particle flow in the respiratory system. The greatest challenge in numerical modelling of particle TD is the complexity of human lungs. This thesis mainly focuses on developing numerical models and investigating the effectiveness of aerosol particle inhalation as drug delivery. Particle inhalation and deposition in human lungs is affected by the lung anatomy, breathing pattern and particle properties (Rissler et al. 2017). Therefore, airflow dynamics and inhaled aerosol particle transport in the lung airways are significant for human health; thus it is important to measure both the efficiency of inhaled drug therapy and the health implications of air pollution (Deng et al. 2018). Further, the lung airways become larger as people grow into adults, and the shape of the airway structure and breathing habits change. Therefore, aging is an important factor in respiratory health. Hence, a comprehensive age-specified particle TD study is necessary to better predict drug delivery to the targeted position in a human lung. This study aims to develop an advanced and efficient three-dimensional (3D) numerical model to analyse airflow characteristics and aerosol particle TD in human lungs. The model is used to analyse the contribution of fundamental impaction and diffusion mechanisms for nanoand microscale particle TD in age-specific terminal bronchiole airways. The outcomes of this study will help improve the effectiveness of delivery of drug aerosols into human lungs to treat obstructive lung diseases including asthma, lung cancer and COPD. In addition, the inhalation of different types of pollutant particles into human lungs is investigated further to understand the consequence of the pollution particle on lung health

Homogenization of a Multiscale Viscoelastic Model with Nonlocal Damping, Application to the Human Lungs

International audienceWe are interested in the mathematical modeling of the deformation of the human lung tissue, called the lung parenchyma, during the respiration process. The parenchyma is a foam–like elastic material containing millions of air–filled alveoli connected by a tree– shaped network of airways. In this study, the parenchyma is governed by the linearized elasticity equations and the air movement in the tree by the Poiseuille law in each airway. The geometric arrangement of the alveoli is assumed to be periodic with a small period ε > 0. We use the two–scale convergence theory to study the asymptotic behavior as ε goes to zero. The effect of the network of airways is described by a nonlocal operator and we propose a simple geometrical setting for which we show that this operator converges as ε goes to zero. We identify in the limit the equations modeling the homogenized behavior under an abstract convergence condition on this nonlocal operator. We derive some mechanical properties of the limit material by studying the homogenized equations: the limit model is nonlocal both in space and time if the parenchyma material is considered compressible, but only in space if it is incompressible. Finally, we propose a numerical method to solve the homogenized equations and we study numerically a few properties of the homogenized parenchyma model

CFD Study of the Flow Field and Particle Dispersion and Deposition in the Upper Human Respiratory System

Das Einatmen von Partikeln in den menschlichen Körper hat zwei verschiedene Aspekte im Hinblick auf die Gesundheit des Menschen. Einerseits existieren schädliche Partikel wie beispielsweise Feinstaub in der Umwelt, der nach Eintreten in den menschlichen Körper Krankheiten wie Herzerkrankungen und Erkrankungen der Atemwege auslösen kann, und der sogar zum Tod führen kann. Hier sind insbesondere Partikel, die kleiner als 2,5 µm sind, relevant. Andererseits ist es in der medizinischen Therapie einiger Atemwegerkrankungen wünschenswert, gezielt Partikel den Atemwegen zuzuführen. Die medikamentöse Aerosol-Therapie, bei der das Medikament durch den nasalen oder oralen Atemweg in die Lunge oder einen anderen Ort des Atemtrakts gebracht wird, wird gern verwendet, um Krankheiten wie z.B. Asthma oder chronisch obstruktive Lungenerkrankungen zu behandeln. Diese Therapie hat den Vorteil der kleinen Dosierung, der minimalen systemischen Nebenwirkungen und der schnellen Wirkung. Das Medikament soll hier tief in die Lunge, in der die Krankheit auftritt, eindringen. Die typische Größe dieser Partikel liegt im Bereich von 1 bis 5 µm. Fokus ist die gezielte Steuerung des Medikaments in spezielle Regionen wie beispielsweise zu einer Tumorposition, sodass Nebenwirkungen durch Ablagerung in anderen Regionen vermieden werden. Ein verbessertes Verständnis des Gesamtprozesses beinhaltet die Kenntnis der charakteristischen Luftströmung und des Partikeltransports sowie deren gegenseitige Beeinflussung. In der vorliegenden Arbeit, in der die Luftströmung sowie die Partikelverteilung und -ablagerung in den menschlichen oberen Atemwegen untersucht werden, werden vier verschiedene Geometrien verwendet: die verengte Luftröhre, das auf einem Gussstück basierende Mund-Rachen-Modell, das auf Computertomographie (CT) basierende Mund-Rachen-Modell und das auf CT-Skans basierende Nasenhöhlen-Modell. Die Software NeuRa2 wird zur Generierung des numerischen Oberflächengitters verwendet und ANSYS ICEM CFD-11.0, um Volumengitter zu erzeugen. Ein-Weg- und Zwei-Wege-Kopplung zwischen der Gasphase und den Partikeln werden in der Arbeit in Abhängigkeit verschiedener Partikelvolumenanteile angewendet. Dreidimensionale inkompressible Navier-Stokes (N-S) Gleichungen werden zur Beschreibung der Luftströmung verwendet. Large Eddy Simulation (LES) wird zur Modellierung der turbulenten Strömung herangezogen, und das Smagorinsky Feinskalen-Modell sowie das dynamische Smagorinsky Modell dienen der Beschreibung der kleinen turbulenten Skalen. Unter der Annahme eines großen Partikel-Luft Dichteverhältnisses, der Vernachlässigbarkeit der Partikelrotation und der Kollision zwischen den Partikeln sowie der Annahme, dass die Trägheitskraft die Partikelbewegung dominiert, werde Lagrange-Gleichungen herangezogen, um die Bewegung der Partikel zu modellieren. Im Falle von Partikeln, die kleiner als ein Mikrometer sind, wird die Brownsche Kraft zusätzlich berücksichtigt. Zur Lösung der Gleichungen wird die Software-Plattform OpenFOAM 1.5 benutzt, für die neue Solver entwickelt werden, die die Luftströmung mit LES und die Teilchenbewegung mit Hilfe einer Lagrange-Formulierung lösen können. Abhängig von der Partikelbeladung wird Ein-Weg- oder Zwei-Wege-Kopplung mit oder ohne Berücksichtigung des Einflusses des Partikelimpulses auf die Gasphase verwendet. Zunächst wird die Luftgeschwindigkeit an der Mittellinie und in unterschiedlichen Querschnitten stromabwärts der Glottis in der verengten Luftröhre mit numerischen Ergebnissen und experimentellen Daten aus der Literatur verglichen, hier wird ein Modell der Reynolds-gemittelten Navier-Stokes-Gleichungen (RANS) bei niedriger Reynolds-Zahl, das k-omega; Modell, verwendet. Die hier verwendete Methode verbessert die vorliegenden Literaturergebnisse, sodass sie die Basis für weitere Berechnungen in den verbleibenden Geometrien bildet. Die Luftströmung wird im Gussstück-basierten Mund-Rachen-Modell für drei verschiedene Inhalationsgeschwindigkeiten simuliert. Die numerischen Ergebnisse zeigen, dass das Geschwindigkeitsfeld der instationären Luftströmung sehr stark vom mittleren Geschwindigkeitsfeld abweicht, dies gilt insbesondere für das Auftreten von Wirbeln. Die numerische Simulation zeigt, dass die Partikelablagerung von der Partikelgröße, ihrer Ausgangsposition, der Inhalationsgeschwindigkeit sowie von der Geometrie abhängt. Turbulenz und Existenz von Rezirkulationszonen haben ebenfalls großen Einfluss auf den Partikeltransport. Eine polydisperse Partikelverteilung, die aus Messungen an einem Trockenpulver-Inhalator zur Verfügung steht, wird ebenfalls zur Simulation herangezogen. In diesem Fall wird Zwei-Wege-Kopplung verwendet. Polydisperse Partikelablagerung zeigt im Vergleich zur monodispersen Partikelablagerung stark unterschiedliche Charakteristika. Deshalb ist es notwendig, polydisperse Partikelverteilung und Zwei-Wege-Kopplung zu verwenden, wenn die reale medikamentöse Dosis eines Hubs berücksichtigt wird, die bei der klinischen Behandlung Anwendung findet. Um das Strömungsfeld bei einer realistischeren zeitabhängigen Inhalation zu untersuchen, wird eine numerische Simulation für das Gussstück-basierte Mund-Rachen-Modell unter den gleichen Bedingungen durchgeführt. Die Untersuchung zeigt, dass das Strömungsfeld signifikant verschieden ist in der beschleunigenden und der verlangsamenden Phase der Inhalation: In der Beschleunigungsphase ist die Luftströmung laminar während sie in der verlangsamenden Phase eher turbulent ist. Zur Untersuchung des Einflusses geometrischer Eigenschaften auf die Partikelablagerung werden numerische Simulationen für das CT-basierte Mund-Rachen-Modell durchgeführt. Im Ergebnis ist das Strömungsfeld im CT-basierten Mund-Rachen-Modell sehr verschieden von dem im Gussstück-basierten Mund-Rachen-Modell. Obwohl das Geschwindigkeitsfeld sowohl im mittleren als auch im zeitabhängigen Fall ähnlich ist, hat das Strömungsfeld ein sehr kompliziertes Wirbelfeld mit hoher räumlicher und zeitlicher Dynamik. Partikel der Größe 2 µm können den Pharynx passieren, sich in der Luftröhre ablagern oder weiter in die Lungenregion vordringen. Um die Eigenschaften des Geschwindigkeitsfelds in der Nasenhöhle zu untersuchen, wurde ein geometrisches Modell der Nasenhöhle aus CT-Skans konstruiert. Die numerischen Ergebnisse zeigen, dass die Luft durch die Hauptluft-Passage der Nasenhöhle fließt und nur wenig Luft die Spitzen der Nasengänge und der olfaktorischen Region erreicht