Numerical solving of relationship between true and false lumen in acute aortic dissection

Aorta, kao osnovni i najveći krvni sud u čoveku, neprekidno je izložena visokom pulzativnom pritisku i smičućim silama. Disekcija aorte predstavlja veoma ozbiljno i urgentno stanje, u kojem dolazi do cepanja i raslojavanja unutrašnjeg sloja aortnog zida, dok spoljnji sloj ostaje netaknut. Numeričke simulacije dinamičkog ponašanja fluida-krvi u aorti sa disekcijom mogu dosta pomoći lekarima, jer daju uvid u dalji razvoj bolesti. Osnovni metod koji je korišćen u ovom radu jeste metod konačnih elemenata (MKE). Brzine strujanja fluida, pritisaka i smičućih napona u čvorovima konačnih elemenata određuju se u karakterističnim tačkama pulzatornog strujanja krvi. U jednom delu rada, primenom komercijalnih softvera, izvršene su trodimenzionalne rekonstrukcije medicinskih snimaka, a potom, primenom softvera koji je razvijen u Istraživačko razvojnom centru za bioinženjering, sprovedeno je numeričko rešavanje odnosa pravog i lažnog lumena akutne aortne disekcije. Osnovni cilj teze je da se primenom numeričkih simulacija odrede pritisci, smičući naponi i brzine u pravom i lažnom lumenu čime se dobija jasna slika njihovog međusobnog odnosa. Virtuelnim simuliranjem efekta operacije (isecanjem uzlazne aorte i zamene tubus graftom) određuju se protoci kroz bočne opstruirane grane aorte zahvaćene disekcijom, što pokazuje kako hirurški zahvat zamene uzlazne aorte i prekidanje protoka lažnog lumena, ima uticaj na protok kroz grane aortnog luka i visceralne grane (grane abdominalne aorte). Određivanjem von Mizesovih napona u zidu lažnog lumena dobijaju se potencijalna mesta rupture aorte. Ovim putem se neinvazivnim pristupom određuje rizik od nastanka rupture aorte i daje prednost ovom metodu, umesto kriterijuma maksimalnog prečnika.Aorta, as the main and the largest blood vessel in the human body, is constantly exposed to high pulse pressure and shear forces. Aortic dissection is a very serious condition and medical emergency, which leads to tearing and delamination of the inner layer of the aortic wall, while the outer layer remains intact. Numerical simulations of the dynamic behavior of fluid-blood in the aorta dissection can be of great help to doctors, because they provide insight into further development of the disease. The main method used in this paper is the finite element method (FEM). Fluid velocity, pressure and wall shear stress in nodes of finite elements are determined by specific points of the pulsatile blood flow. One section of the paper focuses on a three-dimensional reconstruction of medical images using a commercial software and in the next section, by using the software developed in the Research and Development Centre for Bioengineering, the numerical solution of relations between true and false lumens of acute aortic dissection is performed. The main objective of the thesis is to determine pressures, wall shear stress and velocity in the true and false lumen by applying numerical simulations, which gives a clear picture of their relationship. Virtual simulation of the effects of the operation (by cutting the ascending aorta and replacing it with the stent graft) determines the flow through the obstructed side branches of aortic dissection, which shows how the surgical intervention of replacing the ascending aorta and interrupting the flow in the false lumen has an impact on the flow through the branches of the aortic arch and the visceral branches (branches of the abdominal aorta). By determining von Mises stresses in the wall of the false lumen, potential points of rupture of the aorta are obtained. In this manner, the risk of rupture of the aorta is determined by using a non-invasive approach, giving this method an advantage over the maximum diameter criterion

Modeling of Arterial Stiffness using Variations of Pulse Transit Time

In this paper, a finite element (FE) modeling is used to model effects of the arterial stiffness on the different signal patterns of the pulse transit time (PTT). Several different breathing patterns of the three subjects are measured with PTT signal and corresponding finite element model of the straight elastic artery is applied. The computational fluid-structure model provides arterial elastic behavior and fitting procedure was applied in order to estimate Young's module of stiffness of the artery. It was found that approximately same elastic Young's module can be fitted for specific subject with different breathing patterns which validate this methodology for possible noninvasive determination of the arterial stiffness

Numerical solving of relationship between true and false lumen in acute aortic dissection

Aorta, kao osnovni i najveći krvni sud u čoveku, neprekidno je izložena visokom pulzativnom pritisku i smičućim silama. Disekcija aorte predstavlja veoma ozbiljno i urgentno stanje, u kojem dolazi do cepanja i raslojavanja unutrašnjeg sloja aortnog zida, dok spoljnji sloj ostaje netaknut. Numeričke simulacije dinamičkog ponašanja fluida-krvi u aorti sa disekcijom mogu dosta pomoći lekarima, jer daju uvid u dalji razvoj bolesti. Osnovni metod koji je korišćen u ovom radu jeste metod konačnih elemenata (MKE). Brzine strujanja fluida, pritisaka i smičućih napona u čvorovima konačnih elemenata određuju se u karakterističnim tačkama pulzatornog strujanja krvi. U jednom delu rada, primenom komercijalnih softvera, izvršene su trodimenzionalne rekonstrukcije medicinskih snimaka, a potom, primenom softvera koji je razvijen u Istraživačko razvojnom centru za bioinženjering, sprovedeno je numeričko rešavanje odnosa pravog i lažnog lumena akutne aortne disekcije. Osnovni cilj teze je da se primenom numeričkih simulacija odrede pritisci, smičući naponi i brzine u pravom i lažnom lumenu čime se dobija jasna slika njihovog međusobnog odnosa. Virtuelnim simuliranjem efekta operacije (isecanjem uzlazne aorte i zamene tubus graftom) određuju se protoci kroz bočne opstruirane grane aorte zahvaćene disekcijom, što pokazuje kako hirurški zahvat zamene uzlazne aorte i prekidanje protoka lažnog lumena, ima uticaj na protok kroz grane aortnog luka i visceralne grane (grane abdominalne aorte). Određivanjem von Mizesovih napona u zidu lažnog lumena dobijaju se potencijalna mesta rupture aorte. Ovim putem se neinvazivnim pristupom određuje rizik od nastanka rupture aorte i daje prednost ovom metodu, umesto kriterijuma maksimalnog prečnika.Aorta, as the main and the largest blood vessel in the human body, is constantly exposed to high pulse pressure and shear forces. Aortic dissection is a very serious condition and medical emergency, which leads to tearing and delamination of the inner layer of the aortic wall, while the outer layer remains intact. Numerical simulations of the dynamic behavior of fluid-blood in the aorta dissection can be of great help to doctors, because they provide insight into further development of the disease. The main method used in this paper is the finite element method (FEM). Fluid velocity, pressure and wall shear stress in nodes of finite elements are determined by specific points of the pulsatile blood flow. One section of the paper focuses on a three-dimensional reconstruction of medical images using a commercial software and in the next section, by using the software developed in the Research and Development Centre for Bioengineering, the numerical solution of relations between true and false lumens of acute aortic dissection is performed. The main objective of the thesis is to determine pressures, wall shear stress and velocity in the true and false lumen by applying numerical simulations, which gives a clear picture of their relationship. Virtual simulation of the effects of the operation (by cutting the ascending aorta and replacing it with the stent graft) determines the flow through the obstructed side branches of aortic dissection, which shows how the surgical intervention of replacing the ascending aorta and interrupting the flow in the false lumen has an impact on the flow through the branches of the aortic arch and the visceral branches (branches of the abdominal aorta). By determining von Mises stresses in the wall of the false lumen, potential points of rupture of the aorta are obtained. In this manner, the risk of rupture of the aorta is determined by using a non-invasive approach, giving this method an advantage over the maximum diameter criterion

EXPERIMENTAL TESTING AND NUMERICAL MODELLING OF STENTS IN THE CORONARY ARTERIES

In this study, experimental and numerical stent modelling with plaque formation and progression for specific patient in the coronary arteries is described. In the method, section experimental stent testing is firstly described. Then numerical methods with finite element methods are given. Blood flow simulation is described with Navier-Stokes and continuity equation. Blood vessel wall is modelled with nonlinear viscoelastic material properties. The coupling of fluid dynamics and solute dynamics at the endothelium was achieved by the Kedem-Katchalsky equations. The inflammatory process is modelled using three additional reaction-diffusion partial differential equations. In the results section, the examples with rigid and deformable arterial wall with stented and unstented arteries are presented. Effective stress analysis results for stent deployment have been shown. These experimental and numerical methods can give better understanding of stent deployment procedure and arterial wall response in everyday clinical practice

Computational and experimental model of transdermal iontophorethic drug delivery system

The concept of iontophoresis is often applied to increase the transdermal transport of drugs and other bioactive agents into the skin or other tissues. It is a non-invasive drug delivery method which involves electromigration and electroosmosis in addition to diffusion and is shown to be a viable alternative to conventional administration routs such as oral, hypodermic and intravenous injection. In this study we investigated, experimentally and numerically, in vitro drug delivery of dexamethasone sodium phosphate to porcine skin. Different current densities, delivery durations and drug loads were investigated experimentally and introduced as boundary conditions for numerical simulations. Nernst-Planck equation was used for calculation of active substance flux through equivalent model of homogeneous hydrogel and skin layers. The obtained numerical results were in good agreement with experimental observations. A comprehensive in-silico platform, which includes appropriate numerical tools for fitting, could contribute to iontophoretic drug-delivery devices design and correct dosage and drug clearance profiles as well as to perform much faster in-silico experiments to better determine parameters and performance criteria of iontophoretic drug delivery

THREE-DIMENSIONAL BIOMECHANICAL AND VISUALISATION MODEL OF VERTIGO DISEASE IN THE SEMI-CIRCULAR CANAL

Benign paroxysmal positional vertigo (BPPV) is the most common type of vertigo. The symptoms of BPPV typically appear after angular movements of the head. BPPV leads to dizziness, nausea and imbalance. In this study, we examined a model of the semi-circular canal (SCC) with fully 3D three dimensional anatomical data from specific patient. A full Navier-Stokes equations and continuity equations are used for fluid domain with Arbitrary-Lagrangian Eulerian (ALE) formulation for mesh motion of finite element. Fluid-structure interaction for fluid coupling with cupula deformation is used. Particle tracking algorithm is implemented for particle motion. Motion of the otoconia particles which is main cause for BPPV is simulated. Velocity distribution, shear stress and force from endolymph side are presented for patient specific three SCC.  We compared our numerical models with experiments with head moving and nystagmus eye tracking. Numerical simulation can give more details and understanding of the pathology of the specific patient in standard clinical diagnostic and therapy procedure for BPPV

Does the presence of an unerupted lower third molar influence the risk of mandibular angle and condylar fractures?

It has been suggested that unerupted lower third molars (M3) increase the fragility of the mandibular angle and simultaneously decrease the risk of condylar fracture. However, it is unknown whether this applies regardless of the direction and point of impact of the traumatic force. The aim of this study was to investigate the impact of an unerupted M3 on the fragility of the angle and condyle in terms of a force acting from different directions and affecting different regions of the mandible. Computed tomography scans of a human mandible and finite element methodology were used to obtain two three-dimensional models: a model with, and the other without an unerupted M3. A force of 2000 N was applied to three different regions of the models: the symphysis, ipsilateral body, and contralateral body, respectively. When the force was applied to the mandibular body, the results revealed increased angle fragility in cases with unerupted M3. When the force was applied to the symphysis, the condyle region showed higher fragility, irrespective of the presence of an unerupted M3. In summary, fragility of the angle and condyle regions depends on the presence of an unerupted M3 and on the direction and point of impact of the force

Occlusal load distribution through the cortical and trabecular bone of the human mid-facial skeleton in natural dentition: A three-dimensional finite element study

Understanding of the occlusal load distribution through the mid-facial skeleton in natural dentition is essential because alterations in magnitude and/or direction of occlusal forces may cause remarkable changes in cortical and trabecular bone structure. Previous analyses by strain gauge technique, photoelastic and, more recently, finite element (FE) methods provided no direct evidence for occlusal load distribution through the cortical and trabecular bone compartments individually. Therefore, we developed an improved three-dimensional FE model of the human skull in order to clarify the distribution of occlusal forces through the cortical and trabecular bone during habitual masticatory activities. Particular focus was placed on the load transfer through the anterior and posterior maxilla. The results were presented in von Mises stress (VMS) and the maximum principal stress, and compared to the reported FE and strain gauge data. Our qualitative stress analysis indicates that occlusal forces distribute through the mid-facial skeleton along five vertical and two horizontal buttresses. We demonstrated that cortical bone has a priority in the transfer of occlusal load in the anterior maxilla, whereas both cortical and trabecular bone in the posterior maxilla are equally involved in performing this task Observed site dependence of the occlusal load distribution may help clinicians in creating strategies for implantology and orthodontic treatments. Additionally, the magnitude of VMS in our model was significantly lower in comparison to previous FE models composed only of cortical bone. This finding suggests that both cortical and trabecular bone should be modeled whenever stress will be quantitatively analyzed

Impact of the lower third molar presence and position on the fragility of mandibular angle and condyle: A Three-dimensional finite element study

The aim of the present study was to investigate the influences of the presence and position of a lower third molar (M3) on the fragility of mandibular angle and condyle, using finite element analysis. From computed tomographic scans of a human mandible with normally erupted M3, two additional virtual models were generated: a mandibular model with partially impacted M3 and a model without M3. Two cases of impact were considered: a frontal and a lateral blow. The results are based on the chromatic analysis of the distributed von Mises and principal stresses, and calculation of their failure indices. In the frontal blow, the angle region showed the highest stress in the case with partially impacted M3, and the condylar region in the case without M3. Compressive stresses were dominant but caused no failure. Tensile stresses were recorded in the retromolar areas, but caused failure only in the case with partially impacted M3. In the lateral blow, the stress concentrated at the point of impact, in the ipsilateral and contralateral angle and condylar regions. The highest stresses were recorded in the case with partially impacted M3. Tensile stresses caused the failure on the ipsilateral side, whereas compressive stresses on the contralateral side

Microstructural properties of the mid-facial bones in relation to the distribution of occlusal loading

Although the concept of the occlusal load transfer through the facial skeleton along the buttresses has been extensively studied, there has been no study to link microarchitecture of the mid-facial bones to the occlusal load distribution. The aim of this study was to analyze micro-structural properties of the mid-facial bones in relation to occlusal stress. The study was performed by combining the three-dimensional finite element analysis (3D FEA) and micro-computed tomography analysis (micro-CT). Clenching was simulated on the computer model of the adult male human skull which was also used as a source of bone specimens. After the PEA was run, stress was measured at the specific sites in cortical shell and trabecular bone of the model along and between the buttresses. From the corresponding sites on the skull, twenty-five cortical and thirteen cancellous bone specimens were harvested. The specimens were classified into high stress or low stress group based on the stress levels measured via the FEA. Micro-architecture of each specimen was assessed by micro-CT. In the high stress group, cortical bone showed a tendency toward greater thickness and density, lower porosity, and greater pore separation. Stress-related differences in microstructure between the groups were more pronounced in trabecular bone, which showed significantly greater bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) in the high stress group. Our results suggest that the mid-facial bones in the adult dentate male skull exhibit regional variations in cortical and trabecular bone micro-architecture that could be a consequence of different occlusa