Crestal placement of short plateau implants in compromised jaws may cause implant failure due to bone overstress. The aim was to evaluate the impact of different sized implants on adjacent bone overload and the implant load-bearing ability in terms of the proposed index-ultimate functional load (UFL). Three-dimensional models of osseointegrated implants placed in types III and IV bone were analysed by the FEM for the case of patient-specific variations in cortical bone elasticity modulus. Maximum von Mises stresses in surrounding bone were calculated and compared with the cortical and cancellous bone ultimate strength characteristics to determine the UFL index for the studied implants. The implant UFL magnitudes were influenced by their dimensions, bone elasticity, and quality. The implant load-bearing ability was predetermined by cancellous bone strength. The maxilla with moderate elasticity modulus allows for the placement of wide short screwless implants in the compromised maxilla molar site with good clinical perspective.
- Klíčová slova
- FEM, bone quality, plateau implant, stress analysis, ultimate strength,
- MeSH
- analýza metodou konečných prvků MeSH
- lidé MeSH
- maxila * chirurgie MeSH
- mechanický stres MeSH
- modul pružnosti MeSH
- prognóza MeSH
- zubní implantáty * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- zubní implantáty * MeSH
A mathematical model of myocardial perfusion based on the lattice Boltzmann method (LBM) is proposed and its applicability is investigated in both healthy and diseased cases. The myocardium is conceptualized as a porous material in which the transport and mass transfer of a contrast agent in blood flow is studied. The results of myocardial perfusion obtained using LBM in 1D and 2D are confronted with previously reported results in the literature and the results obtained using the mixed-hybrid finite element method. Since LBM is not suitable for simulating flow in heterogeneous porous media, a simplified and computationally efficient 1D-analog approach to 2D diseased case is proposed and its applicability discussed.
- Klíčová slova
- advection–diffusion problem, contrast agent transport, lattice Boltzmann method, magnetic resonance imaging, mixed‐hybrid finite element method, myocardial perfusion,
- MeSH
- analýza metodou konečných prvků * MeSH
- kontrastní látky MeSH
- koronární cirkulace fyziologie MeSH
- lidé MeSH
- modely kardiovaskulární * MeSH
- počítačová simulace MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- kontrastní látky MeSH
Abdominal aortic aneurysm (AAA) disease, the local enlargement of the infrarenal aorta, is a serious condition that causes many deaths, especially in men exceeding 65 years of age. Over the past quarter of a century, computational biomechanical models have been developed towards the assessment of AAA risk of rupture, technology that is now on the verge of being integrated within the clinical decision-making process. The modeling of AAA requires a holistic understanding of the clinical problem, in order to set appropriate modeling assumptions and to draw sound conclusions from the simulation results. In this article we summarize and critically discuss the proposed modeling approaches and report the outcome of clinical validation studies for a number of biomechanics-based rupture risk indices. Whilst most of the aspects concerning computational mechanics have already been settled, it is the exploration of the failure properties of the AAA wall and the acquisition of robust input data for simulations that has the greatest potential for the further improvement of this technology.
- Klíčová slova
- abdominal aortic aneurysm, modeling, ruptuer risk assessment, vascular biomechanics,
- MeSH
- aneurysma břišní aorty * MeSH
- aorta abdominalis MeSH
- biomechanika MeSH
- hodnocení rizik MeSH
- klinická relevance MeSH
- lidé MeSH
- mechanický stres MeSH
- modely kardiovaskulární MeSH
- ruptura aorty * MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
We present comprehensive biomechanical analyses of abdominal aortic aneurysms (AAA) for 43 patients. We compare stress magnitudes and stress distributions within arterial walls of abdominal aortic aneurysms (AAA) obtained using two simulation and modelling methods: (a) Fully automated and computationally very efficient linear method embedded in the software platform Biomechanics based Prediction of Aneurysm Rupture Risk (BioPARR), freely available from https://bioparr.mech.uwa.edu.au/; (b) More complex and much more computationally demanding Non-Linear Iterative Stress Analysis (Non-LISA) that uses a non-linear inverse iterative approach and strongly non-linear material model. Both methods predicted localised high stress zones with over 90% of AAA model volume fraction subjected to stress below 20% of the 99th percentile maximum principal stress. However, for the non-linear iterative method, the peak maximum principal stress (and 99th percentile maximum principal stress) was higher and the stress magnitude in the low stress area lower than for the automated linear method embedded in BioPARR. Differences between the stress distributions obtained using the two methods tended to be particularly pronounced in the areas where the AAA curvature was large. Performance of the selected characteristic features of the stress fields (we used 99th percentile maximum principal stress) obtained using BioPARR and Non-LISA in distinguishing between the AAAs that would rupture and remain intact was for practical purposes the same for both methods.
- Klíčová slova
- abdominal aortic aneurysm, finite element method, patient-specific modelling, rupture, stress,
- MeSH
- analýza metodou konečných prvků MeSH
- aneurysma břišní aorty * MeSH
- aorta abdominalis MeSH
- biomechanika MeSH
- lidé MeSH
- mechanický stres MeSH
- modely kardiovaskulární MeSH
- ruptura aorty * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Physiologically realistic results are the aim of every blood flow simulation. This is not different in aorto-coronary bypasses where the properties of the coronary circulation may significantly affect the relevance of the performed simulations. By considering three patient-specific bypass geometries, the present article focuses on two aspects of the coronary blood flow - its phasic flow pattern and its behaviour affected by blood rheology. For the phasic flow property, a multiscale modelling approach is chosen as a means to assess the ability of five different types of coronary boundary conditions (mean arterial pressure, Windkessel model and three lumped parameter models) to attain realistic coronary haemodynamics. From the analysed variants of boundary conditions, the best option in terms of physiological characteristics and its potential for use in patient-based simulations, is utilised to account for the effect of shear-dependent viscosity on the resulting haemodynamics and wall shear stress stimulation. Aside from the Newtonian model, the blood rheology is approximated by two non-Newtonian models in order to determine whether the choice of a viscosity model is important in simulations involving coronary circulation. A comprehensive analysis of obtained results demonstrated notable superiority of all lumped parameter models, especially in comparison to the constant outlet pressure, which regardless of bypass type gave overestimated and physiologically misleading results. In terms of rheology, it was noted that blood in undamaged coronary arteries behaves as a Newtonian fluid, whereas in vessels with atypical lumen geometry, such as that of anastomosis or stenosis, its shear-thinning behaviour should not be ignored.
- Klíčová slova
- Windkessel model, coronary circulation, lumped parameter model, multiscale approach, patient-specific geometry, shear-thinning non-Newtonian fluid,
- MeSH
- hemodynamika * MeSH
- koronární cévy * chirurgie MeSH
- koronární cirkulace MeSH
- lidé MeSH
- mechanický stres MeSH
- modely kardiovaskulární MeSH
- počítačová simulace MeSH
- rychlost toku krve MeSH
- viskozita MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
This article focuses on the problem of maximal compliance design of a hyper-elastic solid with the optimal design of human skin grafts as the application in mind. The solution method is a phasefield-based topology optimization method that supposes multiple local phasefields and a minimum distance constraint in order to prevent the phasefields from merging. Consequently, structurally disintegrating solutions such as by the coalescence of voids can be prevented. The method is used to find an optimal graft meshing pattern for a sample that is subjected to a biaxial extension of up to 150%, which corresponds to an expansion ratio of 1 : 2.25. Three prospective unitcell solutions that exhibit meta-material behavior are proposed for a periodic graft pattern. The results are a step toward improving the skin graft meshing efficiency. This work does not cover experimental validation.
- MeSH
- kůže * MeSH
- lidé MeSH
- prospektivní studie MeSH
- transplantace kůže * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
PURPOSE: Investigation of trabecular bone strength and compaction is important for fracture risk prediction. At 1-2% compressive strain, trabecular bone undergoes strain softening, which may lead to numerical instabilities and mesh dependency in classical local damage-plastic models. The aim of this work is to improve our continuum damage-plastic model of bone by reducing the influence of finite element mesh size under large compression. METHODOLOGY: This spurious numerical phenomenon may be circumvented by incorporating the nonlocal effect of cumulated plastic strain into the constitutive law. To this end, an over-nonlocal implicit gradient model of bone is developed and implemented into the finite element software ABAQUS using a user element subroutine. The ability of the model to detect the regions of bone failure is tested against experimental stepwise loading data of 16 human trabecular bone biopsies. FINDINGS: The numerical outcomes of the nonlocal model revealed reduction of finite element mesh dependency compared with the local damage-plastic model. Furthermore, it helped reduce the computational costs of large-strain compression simulations. ORIGINALITY: To the best of our knowledge, the proposed model is the first to predict the failure and densification of trabecular bone up to large compression independently of finite element mesh size. The current development enables the analysis of trabecular bone compaction as in osteoporotic fractures and implant migration, where large deformation of bone plays a key role.
- Klíčová slova
- bone localization, densification, large deformation, nonlocal damage, softening,
- MeSH
- algoritmy MeSH
- biologické modely * MeSH
- biomechanika fyziologie MeSH
- fraktury kostí MeSH
- kosti a kostní tkáň fyziologie MeSH
- lidé MeSH
- pevnost v tlaku fyziologie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Considering the fact that hemodynamics plays an important role in the patency and overall performance of implanted bypass grafts, this work presents a numerical investigation of pulsatile non-Newtonian blood flow in three different patient-specific aorto-coronary bypasses. The three bypass models are distinguished from each other by the number of distal side-to-side and end-to-side anastomoses and denoted as single, double and triple bypasses. The mathematical model in the form of time-dependent nonlinear system of incompressible Navier-Stokes equations is coupled with the Carreau-Yasuda model describing the shear-thinning property of human blood and numerically solved using the principle of the SIMPLE algorithm and cell-centred finite volume method formulated for hybrid unstructured tetrahedral grids. The numerical results computed for non-Newtonian and Newtonian blood flow in the three aorto-coronary bypasses are compared and analysed with emphasis placed on the distribution of cycle-averaged wall shear stress and oscillatory shear index. As shown in this study, the non-Newtonian blood flow in all of the considered bypass models does not significantly differ from the Newtonian one. Our observations further suggest that, especially in the case of sequential grafts, the resulting flow field and shear stimulation are strongly influenced by the diameter of the vessels involved in the bypassing.
- Klíčová slova
- Carreau-Yasuda model, SIMPLE algorithm, finite volume method, hybrid grid system, patient-specific aorto-coronary bypass, pulsatile blood flow,
- MeSH
- algoritmy MeSH
- hemodynamika fyziologie MeSH
- koronární bypass metody MeSH
- koronární cévy chirurgie MeSH
- lidé MeSH
- mechanický stres MeSH
- rychlost toku krve fyziologie MeSH
- teoretické modely MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
When a patient is examined by positron emission tomography (PET), radiotracer dose amount (activity) has to be determined. However, the rules for activity correction according to patients' weight used nowadays do not correspond with practical experience. Very high image quality is achieved for slim patients, whereas noisy images are produced for obese patients. There is opportunity to modify the correction rule with the aim to equalize image quality within the broad spectrum of patients and to diminish radiation risk to slim patients, with special importance for children. We have built a model of a particular PET scanner and approximated human trunk, which is our region of interest, by a cylindrical model with segments of liver, outer adipose tissue, and the rest. We have performed Monte Carlo simulations of PET imaging using the GATE simulation package. Under reasonably simplifying assumptions and for special parameters, we have developed curves that recommend amount of injected activity based on body parameters to give PET images of constant quality, the quality being expressed in terms of noise equivalent counts. The dependence qualitatively differs from the rules used in clinical practice nowadays, and the results indicate potential for improvement.
- Klíčová slova
- Monte Carlo simulation, biological system modeling, image quality, positron emission tomography,
- MeSH
- biologické modely MeSH
- dávka záření * MeSH
- fantomy radiodiagnostické MeSH
- index tělesné hmotnosti MeSH
- lidé MeSH
- metoda Monte Carlo * MeSH
- počítačová rentgenová tomografie MeSH
- počítačová simulace MeSH
- počítačové zpracování obrazu MeSH
- pozitronová emisní tomografie metody MeSH
- radioaktivní indikátory MeSH
- trup diagnostické zobrazování fyziologie MeSH
- velikost těla fyziologie MeSH
- výpočet dávky léku * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- radioaktivní indikátory MeSH
