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  • 1.
    Banaem, Hossein Y.
    et al.
    Tehran University of Medical Sciences, Iran.
    Ahmadian, Alireza
    Tehran University of Medical Sciences, Iran.
    Saberi, Hooshangh
    Tehran University of Medical Sciences, Iran.
    Daneshmehr, Alireza
    Univiversity of Tehran, Iran.
    Khodadad, Davood
    Tehran University of Medical Sciences, Iran.
    Brain tumor modeling: glioma growth and interaction with chemotherapy2011In: Proc. SPIE 8285, International Conference on Graphic and Image Processing (ICGIP 2011), SPIE - International Society for Optical Engineering, 2011, article id 82851MConference paper (Refereed)
    Abstract [en]

    In last decade increasingly mathematical models of tumor growths have been studied, particularly on solid tumors which growth mainly caused by cellular proliferation. In this paper we propose a modified model to simulate the growth of gliomas in different stages. Glioma growth is modeled by a reaction-advection-diffusion. We begin with a model of untreated gliomas and continue with models of polyclonal glioma following chemotherapy. From relatively simple assumptions involving homogeneous brain tissue bounded by a few gross anatomical landmarks (ventricles and skull) the models have been expanded to include heterogeneous brain tissue with different motilities of glioma cells in grey and white matter. Tumor growth is characterized by a dangerous change in the control mechanisms, which normally maintain a balance between the rate of proliferation and the rate of apoptosis (controlled cell death). Result shows that this model closes to clinical finding and can simulate brain tumor behavior properly.

  • 2.
    Bergström, Per
    et al.
    Luleå University of Technology.
    Khodadad, Davood
    Luleå University of Technology.
    Hällstig, Emil
    Optronic Partner dp AB.
    Sjödahl, Mikael
    Luleå University of Technology.
    Single Shot Shape Evaluation Using Dual-Wavelength Holographic Reconstructions and Regularization2013In: Fringe 2013: 7th International Workshop on Advanced Optical Imaging and Metrology / [ed] Wolfgang Osten, Springer, 2013, p. 103-108Conference paper (Refereed)
    Abstract [en]

    The aim of this work is to evaluate the shape of a free form object using single shot digital holography. The digital holography results in a gradient field and wrapped phase maps representing the shape of the object. The task is then to find a surface representation from this data which is an inverse problem. To solve this inverse problem we are using regularization with additional shape information from the CAD-model of the measured object.

  • 3.
    Eriksson, Thomas
    et al.
    Graz University of Technology, Austria ; Royal Institute of Technology (KTH).
    Kroon, Martin
    Royal Institute of Technology (KTH).
    Holzapfel, Gerhard A.
    Graz University of Technology, Austria ; Royal Institute of Technology (KTH).
    Influence of medial collagen organization and in-situ axial stretch on saccular cerebral aneurysm growth2009In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 131, no 10, article id 101010Article in journal (Refereed)
    Abstract [en]

    A model for saccular cerebral aneurysm growth, proposed by Kroon and Holzapfel (2007, "A Model for Saccular Cerebral Aneurysm Growth in a Human Middle Cerebral Artery," J. Theor. Biol., 247, pp. 775-787; 2008, "Modeling of Saccular Aneurysm Growth in a Human Middle Cerebral Artery," ASME J. Biomech. Eng., 130, p. 051012), is further investigated. A human middle cerebral artery is modeled as a two-layer cylinder where the layers correspond to the media and the adventitia. The immediate loss of media in the location of the aneurysm is taken to be responsible for the initiation of the aneurysm growth. The aneurysmis regarded as a development of the adventitia, which is composed of several distinct layers of collagen fibers perfectly aligned in specified directions. The collagen fibers are the only load-bearing constituent in the aneurysm wall; their production and degradation depend on the stretch of the wall and are responsible for the aneurysm growth. The anisotropy of the surrounding media was modeled using the strain-energy function proposed by Holzapfel et al. (2000, "A New Constitutive Framework for Arterial Wall Mechanics and a Comparative Study of Material Models," J. Elast., 61, pp. 1-48), which is valid for an elastic material with two families of fibers. It was shown that the inclusion of fibers in the media reduced the maximum principal Cauchy stress and the maximum shear stress in the aneurysm wall. The thickness increase in the aneurysm wall due to material growth was also decreased. Varying the fiber angle in the media from a circumferential direction to a deviation of 10 deg from the circumferential direction did, however, only show a little effect. Altering the axial in situ stretch of the artery had a much larger effect in terms of the steady-state shape of the aneurysm and the resulting stresses in the aneurysm wall. The peak values of the maximum principal stress and the thickness increase both became significantly higher for larger axial stretches.

  • 4.
    Fallqvist, B.
    et al.
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    A chemo-mechanical constitutive model for transiently cross-linked actin networks and a theoretical assessment of their viscoelastic behaviour2013In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 12, no 2, p. 373-382Article in journal (Refereed)
    Abstract [en]

    Biological materials can undergo large deformations and also show viscoelastic behaviour. One such material is the network of actin filaments found in biological cells, giving the cell much of its mechanical stiffness. A theory for predicting the relaxation behaviour of actin networks crosslinked with the cross-linker α-actinin is proposed. The constitutive model is based on a continuum approach involving a neo-Hookean material model, modified in terms of concentration of chemically activated cross-links. The chemical model builds on work done by Spiros (Doctoral thesis, University of British Columbia, Vancouver, Canada, 1998) and has been modified to respond to mechanical stress experienced by the network. The deformation is split into a viscous and elastic part, and a thermodynamically motivated rate equation is assigned for the evolution of viscous deformation. The model predictions were evaluated for stress relaxation tests at different levels of strain and found to be in good agreement with experimental results for actin networks cross-linked with α-actinin.

  • 5.
    Fallqvist, B.
    et al.
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Constitutive modelling of composite biopolymer networks2016In: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 395, p. 51-61Article in journal (Refereed)
    Abstract [en]

    The mechanical behaviour of biopolymer networks is to a large extent determined at a microstructural level where the characteristics of individual filaments and the interactions between them determine the response at a macroscopic level. Phenomena such as viscoelasticity and strain-hardening followed by strain-softening are observed experimentally in these networks, often due to microstructural changes (such as filament sliding, rupture and cross-link debonding). Further, composite structures can also be formed with vastly different mechanical properties as compared to the individual networks. In this present paper, we present a constitutive model presented in a continuum framework aimed at capturing these effects. Special care is taken to formulate thermodynamically consistent evolution laws for dissipative effects. This model, incorporating possible anisotropic network properties, is based on a strain energy function, split into an isochoric and a volumetric part. Generalisation to three dimensions is performed by numerical integration over the unit sphere. Model predictions indicate that the constitutive model is well able to predict the elastic and viscoelastic response of biological networks, and to an extent also composite structures.

  • 6.
    Fallqvist, B.
    et al.
    Royal Institute of Technology, (KTH).
    Kulachenko, A.
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Modelling of cross-linked actin networks: influence of network parameters and cross-link compliance2014In: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 350, p. 57-69Article in journal (Refereed)
    Abstract [en]

    A major structural component of the cell is the actin cytoskeleton, in which actin subunits are polymerised into actin filaments. These networks can be cross-linked by various types of ABPs (Actin Binding Proteins), such as Filamin A. In this paper, the passive response of cross-linked actin filament networks is evaluated, by use of a numerical and continuum network model. For the numerical model, the influence of filament length, statistical dispersion, cross-link compliance (including that representative of Filamin A) and boundary conditions on the mechanical response is evaluated and compared to experimental results. It is found that the introduction of statistical dispersion of filament lengths has a significant influence on the computed results, reducing the network stiffness by several orders of magnitude. Actin networks have previously been shown to have a characteristic transition from an initial bending-dominated to a stretching-dominated regime at larger strains, and the cross-link compliance is shown to shift this transition. The continuum network model, a modified eight-chain polymer model, is evaluated and shown to predict experimental results reasonably well, although a single set of parameters cannot be found to predict the characteristic dependence of filament length for different types of cross-links. Given the vast diversity of cross-linking proteins, the dependence of mechanical response on cross-link compliance signifies the importance of incorporating it properly in models to understand the roles of different types of actin networks and their respective tasks in the cell.

  • 7.
    Fallqvist, Björn
    et al.
    Royal Institute of Technology, (KTH).
    Fielden, Matthew L.
    Royal Institute of Technology, (KTH).
    Pettersson, Torbjörn
    Royal Institute of Technology, (KTH).
    Nordgren, Niklas
    SP Technical Research Institute of Sweden.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Gad, Annica K.B.
    Karolinska Institutet, KI.
    Experimental and computational asessment of F-actin influence in regulating cellular stiffness and relaxation behaviour of fibroblasts2016In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 59, p. 168-184Article in journal (Refereed)
    Abstract [en]

    In biomechanics, a complete understanding of the structures and mechanisms that regulate cellular stiffness at a molecular level remain elusive. In this paper, we have elucidated the role of filamentous actin (F-actin) in regulating elastic and viscous properties of the cytoplasm and the nucleus. Specifically, we performed colloidal-probe atomic force microscopy (AFM) on BjhTERT fibroblast cells incubated with Latrunculin B (LatB), which results in depolymerisation of F-actin, or DMSO control. We found that the treatment with LatB not only reduced cellular stiffness, but also greatly increased the relaxation rate for the cytoplasm in the peripheral region and in the vicinity of the nucleus. We thus conclude that F-actin is a major determinant in not only providing elastic stiffness to the cell, but also in regulating its viscous behaviour. To further investigate the interdependence of different cytoskeletal networks and cell shape, we provided a computational model in a finite element framework. The computational model is based on a split strain energy function of separate cellular constituents, here assumed to be cytoskeletal components, for which a composite strain energy function was defined. We found a significant influence of cell geometry on the predicted mechanical response. Importantly, the relaxation behaviour of the cell can be characterised by a material model with two time constants that have previously been found to predict mechanical behaviour of actin and intermediate filament networks. By merely tuning two effective stiffness parameters, the model predicts experimental results in cells with a partly depolymerised actin cytoskeleton as well as in untreated control. This indicates that actin and intermediate filament networks are instrumental in providing elastic stiffness in response to applied forces, as well as governing the relaxation behaviour over shorter and longer time-scales, respectively.

  • 8.
    Fallqvist, Björn
    et al.
    Royal Institute of Technology, (KTH).
    Kulachenko, Artem
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Cross-link debonding in actin networks: influence on mechanical properties2015In: International Journal of Experimental and Computational Biomechanics, ISSN 1755-8735, Vol. 3, no 1, p. 16-26Article in journal (Refereed)
    Abstract [en]

    The actin cytoskeleton is essential for the continued function and survival of the cell. A peculiar mechanical characteristic of actin networks is their remodelling ability, providing them with a time-dependent response to mechanical forces. In cross-linked actin networks, this behaviour is typically tuned by the binding affinity of the cross-link. We propose that the debonding of a cross-link between filaments can be modelled using a stochastic approach, in which the activation energy for a bond is modified by a term to account for mechanical strain energy. By use of a finite element model, we perform numerical analyses in which we first compare the model behaviour to experimental results. The computed and experimental results are in good agreement for short time scales, but over longer time scales the stress is overestimated. However, it does provide a possible explanation for experimentally observed strain-rate dependence as well as strain-softening at longer time scales.

  • 9.
    Holzapfel, Gerhard A.
    et al.
    Royal Institute of Technology KTH ; Graz University of Technology, Austria.
    Kiousis, Dimitrios E.
    Graz University of Technology, Austria .
    Kroon, Martin
    Royal Institute of Technology KTH.
    On Modelling Multi-Layered Soft Collagenous Tissues2008In: Presented at 8th World Congress on Computational Mechanics, 30 June – 4 July, 2008, Venice, Italy, 2008Conference paper (Refereed)
  • 10.
    Kandušer, Maša
    et al.
    University of Ljubljana, Slovenia.
    Kokalj Imsirovic, Mojca
    University of Ljubljana, Slovenia.
    Ušaj, Marko
    University of Ljubljana, Slovenia.
    The Effect of Lipid Antioxidant α-Tocopherol on Cell Viability and Electrofusion Yield of B16-F1 Cells In Vitro2019In: The Journal of Membrane Biology, ISSN 0022-2631, Vol. 252, no 1, p. 105-114Article in journal (Refereed)
    Abstract [en]

    Induced cell fusion is a powerful method for production of hybridoma in biotechnology and cell vaccines in medical applications. Among different alternatives, physical methods have an advantage, as they do not require any additives. Among them electrofusion, an electroporation-based cell fusion method holds a great promise. Electric pulses cause cell membrane permeabilization and due to pore formation bring cell membrane into the fusogenic state. At the same time, however, they compromise cell viability. We used a train of 8 × 100 µs electric pulses, delivered at 1 Hz with strengths ranging from 400 to 1600 V/cm. We evaluated electrofusion efficiency by dual color microscopy. We determined cell viability, because during electroporation reactive oxygen species are generated affecting cell survival. The novelty of our study is evaluation of the effect of lipid antioxidant α-tocopherol on cell fusion yield and cell viability on mouse B16-F1 cells. Pretreatment with α-tocopherol slowed down dynamic of cell fusion shortly after electroporation. Twenty-four hours later, fusion yields between α-tocopherol treated and untreated cells were comparable. The viability of α-tocopherol pretreated cells was drastically improved. Pretreatment of cells with α-tocopherol improved whole electrofusion process by more than 60%. We believe that α-tocopherol holds great promise to become an important agent to improve cell electrofusion method.

  • 11.
    Kandušer, Maša
    et al.
    University of Ljubljana, Slovenia.
    Ušaj, Marko
    University of Ljubljana, Slovenia.
    Cell electrofusion: past and future perspectives for antibody production and cancer cell vaccines2014In: Expert Opinion on Drug Delivery, ISSN 1742-5247, E-ISSN 1744-7593, Vol. 11, no 12, p. 1885-1898Article in journal (Refereed)
    Abstract [en]

    Introduction: In the past few decades, new methods for drug and gene delivery have been developed, among which electroporation and electrofusion have gained noticeable attention. Lately, advances in the field of immunotherapy have enabled new cancer therapies based on immune response, including monoclonal antibodies and cell vaccines. Efficient cell fusion is needed for both hybridoma production and cell vaccine preparation, and electrofusion is a promising method to achieve this goal.Areas covered: In the present review, we cover new strategies of cancer treatment related to antibody production and cell vaccines. In more detail, cell electroporation and electrofusion are addressed. We briefly describe principles of cell electroporation and focus on electrofusion and its influential factors, with special attention on the fusogenic state of the cell membrane, contact formation, the effect of electrofusion media and cell viability. We end the review with an overview of the very promising field of microfluidic devices for electrofusion.Expert opinion: In our opinion, electrofusion can be a very efficient method for hybridoma and cell vaccine production. Advances in the development of microfluidic devices and a better understanding of the underlying (biological) mechanisms will overcome the current limitations.

  • 12.
    Khodadad, Davood
    et al.
    Luleå University of Technology.
    Bergström, Per
    Luleå University of Technology.
    Hällstig, Emil
    Optronic Partner dp AB.
    Sjödahl, Mikael
    Luleå University of Technology.
    Dual-wavelength digital holography: single shot calibration2014In: Proc. SPIE9203: Interferometry XVII: Techniques and Analysis / [ed] Katherine Creath; Jan Burke; Joanna Schmit, SPIE - International Society for Optical Engineering, 2014, article id 920305Conference paper (Refereed)
    Abstract [en]

    In an on line shape measurement in disturbed environment, use of many wavelengths in order to avoid phase ambiguity may become a problem as it is necessary to acquire all holograms simultaneously due to environmental disturbances. Therefore to make the shape data available the different holograms have to be extracted from a single recorded image in spectral domain. Appropriate cut areas in the Fourier method are therefore of great importance for decoding information carried by different wavelengths. Furthermore using different laser sources, induces aberration and pseudo phase changes which must be compensated. To insure any phase change is only because of the object shape, calibration is therefore indispensable. For this purpose, effects of uncontrolled carrier frequency filtering are discussed. A registration procedure is applied using minimum speckle displacements to find the best cut area to extract and match the interference terms. Both holograms are numerically propagated to a focus plane to avoid any unknown errors. Deviations between a reference known plate and its measurement are found and used for calibration. We demonstrate that phase maps and speckle displacements can be recovered free of chromatic aberrations. To our knowledge, this is the first time that a single shot dual wavelength calibration is reported by defining a criteria to make the spatial filtering automatic avoiding the problems of manual methods. The procedure is shown to give shape accuracy of 35μm with negligible systematic errors using a synthetic wavelength of 1.1 mm.

  • 13.
    Khodadad, Davood
    et al.
    Luleå University of Technology.
    Bergström, Per
    Luleå University of Technology.
    Hällstig, Emil
    Optronic Partner dp AB.
    Sjödahl, Mikael
    Luleå University of Technology.
    Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements2015In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, no 16, p. 5003-5010Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18  mm×18  mm.

  • 14.
    Khodadad, Davood
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Nordebo, Sven
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Mueller, Beat
    Swisstom AG, Switzerland.
    Waldmann, Andreas Daniel
    Swisstom AG, Switzerland.
    Yerworth, Rebecca
    University College London, UK.
    Becher, Tobias
    University Medical Centre Schleswig-Holstein, Germany.
    Frerichs, Inez
    University Medical Centre Schleswig-Holstein, Germany.
    Sophocleous, Louiza
    University of Cyprus, Cyprus.
    Kaam, Anton van
    Emma Children's Hospital, Academic Medical Center, Netherlands ; VU Medical Center, Netherlands.
    Miedema, Martijn
    Emma Children's Hospital, Academic Medical Center, Netherlands.
    Seifnaraghi, Nima
    Middlesex University, UK.
    Bayford, Richard H
    Middlesex University, UK.
    Optimized breath detection algorithm in electrical impedance tomography2018In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 39, no 9, article id 094001Article in journal (Refereed)
    Abstract [en]

    Objective: This paper defines a method for optimizing the breath delineation algorithms used in Electrical Impedance Tomography (EIT). In lung EIT the identification of the breath phases is central for generating tidal impedance variation images, subsequent data analysis and clinical evaluation. The optimisation of these algorithms is particularly important in neonatal care since the existing breath detectors developed for adults may give insufficient reliability in neonates due to their very irregular breathing pattern. Approach: Our approach is generic in the sense that it relies on the definition of a gold standard and the associated definition of detector sensitivity and specificity, an optimisation criterion and a set of detector parameters to be investigated. The gold standard has been defined by 11 clinicians with previous experience with EIT and the performance of our approach is described and validated using a neonatal EIT dataset acquired within the EU-funded CRADL project. Main results: Three different algorithms are proposed that are improving the breath detector performance by adding conditions on 1) maximum tidal breath rate obtained from zero-crossings of the EIT breathing signal, 2) minimum tidal impedance amplitude and 3) minimum tidal breath rate obtained from Time-Frequency (TF) analysis. As a baseline the zero crossing algorithm has been used with some default parameters based on the Swisstom EIT device. Significance: Based on the gold standard, the most crucial parameters of the proposed algorithms are optimised by using a simple exhaustive search and a weighted metric defined in connection with the Receiver Operating Characterics (ROC). This provides a practical way to achieve any desirable trade-off between the sensitivity and the specificity of the detectors.

  • 15.
    Khodadad, Davood
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Nordebo, Sven
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Seifnaraghi, Nima
    The Burroughs, UK.
    Waldmann, Andreas D.
    Swisstom AG, Switzerland.
    Müller, Beat
    Swisstom AG, Switzerland.
    Bayford, Richard
    The Burroughs, UK.
    Breath detection using short-time Fourier transform analysis in electrical impedance tomography2017In: 2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017, IEEE, 2017, , p. 3p. 1-3Conference paper (Refereed)
    Abstract [en]

    Spectral analysis based on short-time Fourier transform (STFT) using Kaiser window is proposed to examine the frequency components of neonates EIT data. In this way, a simultaneous spatial-time-frequency analysis is achieved.

  • 16.
    Khodadad, Davood
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Nordebo, Sven
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Seifnaraghi, Nima
    Middlesex University, UK.
    Yerworth, Rebecca
    University College London, UK.
    Waldmann, Andreas D.
    Swisstom AG. Switzerland.
    Muller, Beat
    Swisstom AG, Switzerland.
    Frerichs, Inez
    University Medical Centre Schleswig-Holstein, Germany.
    Kaam, Anton van
    Emma Children's Hospital, Academic Medical Center, Netherlands.
    Miedema, Martijn
    Emma Children's Hospital, Academic Medical Center, Netherlands.
    Bayford, Richard
    Middlesex University, UK.
    The Value of Phase Angle in Electrical Impedance Tomography Breath Detection2018In: Progress In Electromagnetics Research Symposium 2018, IEEE, 2018, p. 1040-1043Conference paper (Refereed)
    Abstract [en]

    The objective of this paper is to report our investigation demonstrating that the phase angle information of complex impedance could be a simple indicator of a breath cycle in chest Electrical Impedance Tomography (EIT). The study used clinical neonatal EIT data. The results show that measurement of the phase angle from complex EIT data can be used as a complementary information for improving the conventional breath detection algorithms.

  • 17.
    Kondori, Farid Abedan
    et al.
    Umeå universitet, Institutionen för tillämpad fysik och elektronik.
    Yousefi, Shahrouz
    Umeå universitet, Institutionen för tillämpad fysik och elektronik.
    Liu, Li
    Umeå universitet, Institutionen för tillämpad fysik och elektronik.
    Active human gesture capture for diagnosing and treating movement disorders2013In: Proceeding of The Swedish Symposium on Image Analysis (SSBA2013), Gothenburg, Sweden, 2013Conference paper (Other academic)
    Abstract [en]

    Movement disorders prevent many people fromenjoying their daily lives. As with other diseases, diagnosisand analysis are key issues in treating such disorders.Computer vision-based motion capture systems are helpfultools for accomplishing this task. However Classical motiontracking systems suffer from several limitations. First theyare not cost effective. Second these systems cannot detectminute motions accurately. Finally they are spatially limitedto the lab environment where the system is installed. In thisproject, we propose an innovative solution to solve the abovementionedissues. Mounting the camera on human body, webuild a convenient, low cost motion capture system that canbe used by the patient in daily-life activities. We refer tothis system as active motion capture, which is not confinedto the lab environment. Real-time experiments in our labrevealed the robustness and accuracy of the system.

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  • 18.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    A constitutive framework for modelling thin incompressible viscoelastic materials under plane stress in the finite strain regime2011In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 15, no 4, p. 389-406Article in journal (Refereed)
    Abstract [en]

    Rubbers and soft biological tissues may undergo large deformations and are also viscoelastic. The formulation of constitutive models for these materials poses special challenges. In several applications, especially in biomechanics, these materials are also relatively thin, implying that in-plane stresses dominate and that plane stress may therefore be assumed. In the present paper, a constitutive model for viscoelastic materials in the finite strain regime and under the assumption of plane stress is proposed. It is assumed that the relaxation behaviour in the direction of plane stress can be treated separately, which makes it possible to formulate evolution laws for the plastic strains on explicit form at the same time as incompressibility is fulfilled. Experimental results from biomechanics (dynamic inflation of dog aorta) and rubber mechanics (biaxial stretching of rubber sheets) were used to assess the proposed model. The assessment clearly indicates that the model is fully able to predict the experimental outcome for these types of material.

  • 19.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    A constitutive model for smooth muscle including active tone and passive viscoelastic behaviour2010In: Mathematical Medicine and Biology, ISSN 1477-8599, E-ISSN 1477-8602, Vol. 27, no 2, p. 129-155Article in journal (Refereed)
    Abstract [en]

    A new constitutive model for the biomechanical behaviour of smooth muscle tissue is proposed. The active muscle contraction is accomplished by the relative sliding between actin and myosin filaments, comprising contractile units in the smooth muscle cells. The model includes a chemical part, governing the cross-bridge (myosin head) cycling, that is responsible for the filament sliding. The number of activated cross-bridges govern the contractile force generated and also the contraction speed. A strain-energy function is used to describe the mechanical behaviour of the smooth muscle tissue. Besides the active contractile apparatus, the mechanical model also incorporates a passive viscoelastic part. The constitutive model was calibrated with respect to experiments on smooth muscle tissue from swine carotid artery and guinea pig taenia coli, in terms of isometric and isotonic tensile test results. The model was fully able to reproduce the experimental results.

  • 20.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    A continuum mechanics framework and a constitutive model for remodelling of collagen gels and collagenous tissues2010In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 58, no 6, p. 918-933Article in journal (Refereed)
    Abstract [en]

    Collagen is a very important protein of the human body and is responsible for the structural stability of many body components. Furthermore, collagen fibre networks are able to grow and remodel themselves, which enables them to adjust to varying physiological conditions. This remodelling is accomplished by fibre-producing cells, such as fibroblasts. The ability to adjust to new physiological conditions is very important, for example in wound healing. In the present paper, a theoretical framework for modelling collagenous tissues and collagen gels is proposed. Continuum mechanics is employed to describe the kinematics of the collagen, and affine deformations of fibres are assumed. Biological soft tissues can be approximated as being hyperelastic, and the constitutive model for the collagen fabric is therefore formulated in terms of a strain energy function. This strain energy function includes a density function that describes the distribution of the collagen fibre orientation. The density function evolves according to an evolution law, where fibres tend to reorient towards the direction of maximum Cauchy stress. The remodelling of the collagen network is also assumed to include a pre-stretching of collagen fibres, accomplished by fibroblasts. The theoretical framework is applied to experiments performed on collagen gels, where gels were exposed to remodelling under both biaxial and uniaxial constraints. The proposed model was able to predict both the resulting collagen distribution and the resulting stress–strain relationships obtained for the remodelled collagen gels. The influence of the most important model parameters is demonstrated, and it appears that there is a fairly unique set of model parameters that gives an optimal fit to the experimental data.

  • 21.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    A numerical framework for material characterization of inhomogeneous hyperelastic membranes by inverse analysis2010In: Journal of Computational and Applied Mechanics, ISSN 1586-2070, Vol. 234, no 2, p. 563-578Article in journal (Refereed)
    Abstract [en]

    An inverse method for estimating the distributions of the elastic properties of hyperelastic, inhomogeneous membranes is proposed. The material description of the membrane is based on a versatile constitutive model, in which two stiffness parameters govern the nonlinear elastic behaviour of the material. The estimation procedure includes a finite element framework. The two stiffness parameters in the constitutive law are assumed to vary continuously over the inhomogeneous membrane, and in the finite element framework the distributions of the two parameters are approximated using standard linear shape functions. Experimental results are assumed to exist in terms of nodal displacements from a test with known geometry and boundary conditions. The experimental membrane is modelled in the finite element framework, and the deformation of it is predicted. An error function, quantifying the discrepancy between the experimentally obtained deformation pattern and the numerically predicted pattern, is then minimised with respect to the nodal values of the two interpolated parameters. In a number of numerical examples, the proposed procedure is assessed by attempting to reproduce the given random reference distributions of material properties. The proposed estimation method is fully able to reproduce the reference distributions of the two material parameters with excellent accuracy.

  • 22.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    An efficient method for material characterization of hyperelastic anisotropic inhomogeneous membranes based on inverse finite element method and an element partition strategy2010In: Quarterly Journal of Mechanics and Applied Mathematics, ISSN 0033-5614, E-ISSN 1464-3855, Vol. 63, no 2, p. 201-225Article in journal (Refereed)
    Abstract [en]

    An inverse method for estimating the distributions of the nonlinear elastic properties of inhomogeneous and anisotropic membranes is investigated. The material description of the membrane is based on a versatile constitutive model, including four material parameters: two initial stiffness values pertaining to the principal directions of the material, the angle between these principal directions and a reference coordinate system and a parameter related to the level of nonlinearity of the material. The estimation procedure consists of the following three steps: (i) perform experiments on the membranous structure whose properties are to be determined, (ii) define a corresponding finite-element (FE) model and (iii) minimise an error function (with respect to the unknown parameters) that quantifies the deviation between the numerical predictions and the experimental data. For this finite deformation problem, an FE framework for membranous structures exposed to a pressure boundary loading is outlined: the principle of virtual work, its linearisation and the related spatial discretisation. To achieve a robust parameter estimation, an element partition method is employed. In numerical examples, the proposed procedure is assessed by attempting to reproduce given random reference distributions of material fields in a reference membrane. The deviations between the estimated material parameter distributions and the related reference fields are within a few percent in most cases. The standard deviation for the resulting maximum principal stress was consistently below 1%.

  • 23. Kroon, Martin
    An Inverse Method to Estimate the Material Parameters and Wall Stresses of a Saccular Cerebral Aneurysm2008In: Presented at 11th Euromech – Mecamat Conference, 10-14 March, 2008, Torino, Italy, 2008Conference paper (Refereed)
  • 24.
    Kroon, Martin
    Royal Institute of Technology KTH.
    Assessment of three possible criteria for remodelling of collagen gels and collagenous tissues2010In: Presented at ASME Summer Bioengineering Conference, 16-19 June, 2010, ASME Press, 2010, p. 775-776Conference paper (Refereed)
    Abstract [en]

    Collagenous tissues are living structures, in which new material may be added and the structural organisation may change over time. The maintenance of the collagen matrix is accomplished by fibre-producing cells, such as fibroblasts. During maintenance, the extracellular matrix (ECM) influences the development, shape, migration, proliferation, survival, and function of the cells. The mobility of the fibroblasts and their ability to contract the ECM are important properties for a proper maintenance of the ECM [1,2]. The purpose of the present paper is to shed some more light on the interaction between the ECM and the fibre-producing cells. The fibroblasts remodel the collagen gel by reorienting the individual collagen fibres. This reorientation of fibres is described by an evolution law, which depends on a continuum mechanics entity. Three possible choices are assessed: reorientation towards increasing Cauchy stress, increasing elastic stretch, and increasing current stiffness of the material. The model is compared with experimental results, and the three different criteria are evaluated in terms of the predicted distribution of collagen fibres after remodeling and resulting stress-strain relations. Experimental results from tissue equivalents in the form of collagen gels are used when assessing the three criteria [3]. We consider a network of collagen fibres, where the fibres are embedded in a matrix fluid. The collagen fabric and the surrounding fluid are assumed to be the only load-carrying constituents in the material. Embedded in and attached to the collagen fabric is also a population of fibroblasts. The collagen fabric is composed of collagen fibres, which in turn are bundles of collagen fibrils. The deformation of a line element in the matrix is described by the deformation gradient F(X) = ∂x/∂X, which is decomposed according to F = FelFlfFr, see Fig. 1. The fibroblasts’ remodelling of the collagen fabric results in a new matrix configuration Ωr. This deformation of the matrix is described by Fr. The configuration Ωr does not necessarily fulfill equilibrium, and the deformation gradient Flf takes the matrix to the state Ωlf, that fulfils global equilibrium with no external loads applied. Finally, if external loads are applied to the material, the configuration Ωel is attained, and this deformation is described by the deformation gradient Fel.

  • 25.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Cell contraction of an elastic substrate assessed by an axisymmetric model2012In: International Journal of Experimental and Computational Biomechanics, ISSN 1755-8735, Vol. 2, no 1, p. 61-73Article in journal (Refereed)
    Abstract [en]

    In the present paper, a computational model for cell contraction of an elastic substrate is proposed. Axisymmetry is assumed and the cell is represented by its contractile apparatus, which is taken to consist of radially oriented stress fibres. The constitutive behaviour of the contractile apparatus is modelled by use of a strain energy function, and contraction of stress fibres is modelled by giving them a different natural configuration compared with the underlying elastic substrate. The model was compared with experiments, in which fibroblasts were put on an elastic substrate. The contracted cell radius depends on the stiffness of the elastic substrate, and model predictions were compared with the experimental results for different values of the stiffness of the elastic substrate. The model also predicts that the contraction of the cell tends to cause a small crater below the cell, which is qualitatively in agreement with experimental observations.

  • 26.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Influence of dispersion in myosin filament orientation and anisotropic filament contractions in smooth muscle2011In: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 272, no 1, p. 72-82Article in journal (Refereed)
    Abstract [en]

    A new constitutive model for the biomechanical behaviour of smooth muscle tissue is proposed. The active muscle contraction is accomplished by the relative sliding between actin and myosin filaments, comprising contractile units in the smooth muscle cells. The orientation of the myosin filaments, and thereby the contractile units, are taken to exhibit a statistical dispersion around a preferred direction. The number of activated cross-bridges between the actin and myosin filaments governs the contractile force generated by the muscle and also the contraction speed. A strain-energy function is used to describe the mechanical behaviour of the smooth muscle tissue. Besides the active contractile apparatus, the mechanical model also incorporates a passive elastic part. The constitutive model was compared to histological and isometric tensile test results for smooth muscle tissue from swine carotid artery. In order to be able to predict the active stress at different muscle lengths, a filament dispersion significantly larger than the one observed experimentally was required. Furthermore, a comparison of the predicted active stress for a case of uniaxially oriented myosin filaments and a case of filaments with a dispersion based on the experimental histological data shows that the difference in generated stress is noticeable but limited. Thus, the results suggest that myosin filament dispersion alone cannot explain the increase in active muscle stress with increasing muscle stretch.

  • 27. Kroon, Martin
    Mechanical Modelling of Calcium-Activated Contraction of Smooth Muscle Cells2008In: Presented at IUTAM Symposium on Cellular, Molecular and Tissue Mechanics, 18-21 June, 2008, Woods Hole, Massachusetts, USA, 2008Conference paper (Refereed)
  • 28. Kroon, Martin
    Modelling of smooth muscle Cells2008In: Presented at 8th World Congress on Computational Mechanics, 30 June – 4 July, 2008, Venice, Italy, 2008Conference paper (Refereed)
  • 29. Kroon, Martin
    Modelling of Thin Anisotropic Collagen-Dominated Soft Biological Tissue2008In: Presented at 2nd International Conference on Heterogeneous Material Mechanics, 3-8 June, 2008, Huangshan, China, 2008Conference paper (Refereed)
  • 30.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    On the correlation between continuum mechanics entities and cell activity in biological soft tissues: Assessment of three possible criteria for cell-controlled fibre reorientation in collagen gels and collagenous tissues2010In: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 264, no 1, p. 66-76Article in journal (Refereed)
    Abstract [en]

    The biomechanical behaviour of biological cells is of great importance in many physiological processes. One such process is the maintenance of fibrous networks, such as collagenous tissues. The activity of the fibre-producing cells in this type of tissue is very important, and a comprehensive material description needs to incorporate the activity of the cells. In biomechanics, continuum mechanics is often employed to describe deforming solids, and modelling can be much simplified if continuum mechanics entities, such as stress and strain, can be correlated with cell activity. To investigate this, a continuum mechanics framework is employed in which remodelling of a collagen gel is modelled. The remodelling is accomplished by fibroblasts, and the activity of the fibroblasts is linked to the continuum mechanics theory. The constitutive model for the collagen fabric is formulated in terms of a strain energy function, which includes a density function describing the distribution of the collagen fibre orientation. This density function evolves according to an evolution law, where fibroblasts reorient fibres towards the direction of increasing Cauchy stress, elastic deformation, or stiffness. The theoretical framework is applied to experimental results from collagen gels, where gels have undergone remodelling under both biaxial and uniaxial constraint. The analyses indicated that criteria 1 and 2 (Cauchy stress and elastic deformations) are able to predict the collagen fibre distribution after remodelling, whereas criterion 3 (current stiffness) is not. This conclusion is, however, tentative and pertains, strictly speaking, only to fibre remodelling processes, and may not be valid for other types of cell activities.

  • 31.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    Optimal length of smooth muscle assessed by a microstructurally and statistically based constitutive model2011In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 14, no 1, p. 43-52Article in journal (Refereed)
    Abstract [en]

    Smooth muscle exhibits an optimal length at which it is able to generate a maximum amount of force. In this study, the optimal length is assessed by use of a microstructurally and statistically based constitutive model for smooth muscle. The model is based on the sliding filament theory, and a modified version of Hill's mechanical model was adopted. It was conjectured, that a variation in the overlap in the actomyosin contractile units together with a statistical dispersion in the size of the dense bodies are responsible for the optimal length characteristics. The influence of contractile unit length, dense body size and dense body compliance was investigated, and the model was fully able to predict experimental data. The results indicate that the compliance of the dense bodies does not contribute significantly to the total compliance of the contractile apparatus.

  • 32.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Simulation of cerebral aneurysm growth and prediction of evolving rupture risk2011In: Modelling and Simulation in Engineering, ISSN 1687-5591, E-ISSN 1687-5605, article id 289523Article in journal (Refereed)
    Abstract [en]

    Cerebral aneurysms are local expansions of blood vessel walls in the brain blood system. The rupture of an aneurysm is a very severe event associated with a high rate of mortality. When cerebral aneurysms are detected, clinicians need to decide if operation is required. The risk of aneurysm rupture is then compared to the risks associated with the medical intervention. In the present paper, a probabilistic framework for a mechanically based rupture risk assessment of cerebral aneurysms is proposed. The method is based on the assumption that the strength of aneurysmal tissues can be described by a statistical distribution. A structural analysis of the aneurysm in question is performed, and the maximum stress experienced by the aneurysm is compared to the strength distribution. The proposed model was compared with clinical results for ruptured aneurysms in terms of rupture density and accumulated rupture risk as a function of aneurysm size. The model was able to reproduce the clinical results well. The proposed framework may potentially be used under in vivo conditions to predict the risk of rupture for diagnosed aneurysms.

  • 33.
    Murtada, Sae-Il
    et al.
    Royal Institute of Technology (KTH).
    Kroon, Martin
    Royal Institute of Technology (KTH).
    Holzapfel, Gerhard A.
    Graz University of Technology, Austria ; Royal Institute of Technology (KTH).
    A calcium-driven mechanochemical model for prediction of force generation in smooth muscle.2010In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 9, no 6, p. 749-762Article in journal (Refereed)
    Abstract [en]

    A new model for the mechanochemical response of smooth muscle is presented. The focus is on the response of the actin–myosin complex and on the related generation of force (or stress). The chemical (kinetic) model describes the cross-bridge interactions with the thin filament in which the calcium-dependent myosin phosphorylation is the only regulatory mechanism. The new mechanical model is based on Hill’s three-component model and it includes one internal state variable that describes the contraction/relaxation of the contractile units. It is characterized by a strainenergy function and an evolution law incorporating only a few material parameters with clear physical meaning. The proposed model satisfies the second law of thermodynamics. The results of the combined coupled model are broadly consistent with isometric and isotonic experiments on smooth muscle tissue. The simulations suggest that the matrix in which the actin–myosin complex is embedded does have a viscous property. It is straightforward for implementation into a finite element program in order to solve more complex boundary-value problems such as the control of short-term changes in lumen diameter of arteries due to mechanochemical signals.

  • 34.
    Murtada, Sae-Il
    et al.
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Holzapfel, Gerhard A.
    Graz University of Technology, Austria ; Royal Institute of Technology (KTH).
    Modeling the dispersion effects of contractile fibers in smooth muscles2010In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 58, no 12, p. 2065-2082Article in journal (Refereed)
    Abstract [en]

    Micro-structurally based models for smooth muscle contraction are crucial for a better understanding of pathological conditions such as atherosclerosis, incontinence and asthma. It is meaningful that models consider the underlying mechanical structure and the biochemical activation. Hence, a simple mechanochemical model is proposed that includes the dispersion of the orientation of smooth muscle myofilaments and that is capable to capture available experimental data on smooth muscle contraction. This allows a refined study of the effects of myofilament dispersion on the smooth muscle contraction. A classical biochemical model is used to describe the cross-bridge interactions with the thin filament in smooth muscles in which calcium-dependent myosin phosphorylation is the only regulatory mechanism. A novel mechanical model considers the dispersion of the contractile fiber orientations in smooth muscle cells by means of a strain-energy function in terms of one dispersion parameter. All model parameters have a biophysical meaning and may be estimated through comparisons with experimental data. The contraction of the middle layer of a carotid artery is studied numerically. Using a tube the relationships between the internal pressure and the stretches are investigated as functions of the dispersion parameter, which implies a strong influence of the orientation of smooth muscle myofilaments on the contraction response. It is straightforward to implement this model in a finite element code to better analyze more complex boundary-value problems.

  • 35.
    Nicholls, Ian A.
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Karlsson, Björn C. G.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences. Bioorganic & Biophysical Chemistry Laboratory.
    Rosengren, Annika M.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Andersson, Per-Ola
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Method and apparatus for detecting pharmaceuticals in a sample2014Patent (Other (popular science, discussion, etc.))
  • 36.
    Nordebo, Sven
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Dalarsson, Mariana
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Khodadad, Davood
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Müller, Beat
    Swisstom AG, Switzerland.
    Waldermann, Andreas D.
    Swisstom AG, Switzerland.
    Becher, Tobias
    University Medical Centre Schleswig-Holstein, Germany.
    Frerichs, Inez
    University Medical Centre Schleswig-Holstein, Germany.
    Sophocleous, Louiza
    University of Cyprus, Cyprus.
    Sjöberg, Daniel
    Lund University.
    Seifnaraghi, Nima
    Middlesex University, UK.
    Bayford, Richard
    Middlesex University, UK.
    A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 20, article id 205401Article in journal (Refereed)
    Abstract [en]

    Classical homogenization theory based on the Hashin–Shtrikman coated ellipsoids is used to model the changes in the complex valued conductivity (or admittivity) of a lung during tidal breathing. Here, the lung is modeled as a two-phase composite material where the alveolar air-filling corresponds to the inclusion phase. The theory predicts a linear relationship between the real and the imaginary parts of the change in the complex valued conductivity of a lung during tidal breathing, and where the loss cotangent of the change is approximately the same as of the effective background conductivity and hence easy to estimate. The theory is illustrated with numerical examples based on realistic parameter values and frequency ranges used with electrical impedance tomography (EIT). The theory may be potentially useful for imaging and clinical evaluations in connection with lung EIT for respiratory management and control.

  • 37.
    Rems, Lea
    et al.
    University of Ljubljana, Slovenia.
    Ušaj, Marko
    University of Ljubljana, Slovenia.
    Kandušer, Maša
    University of Ljubljana, Slovenia.
    Reberšek, Matej
    University of Ljubljana, Slovenia.
    Miklavčič, Damijan
    University of Ljubljana, Slovenia.
    Pucihar, Gorazd
    University of Ljubljana, Slovenia.
    Cell electrofusion using nanosecond electric pulses2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, article id 3382Article in journal (Refereed)
    Abstract [en]

    Electrofusion is an efficient method for fusing cells using short-duration high-voltage electric pulses. However, electrofusion yields are very low when fusion partner cells differ considerably in their size, since the extent of electroporation (consequently membrane fusogenic state) with conventionally used microsecond pulses depends proportionally on the cell radius. We here propose a new and innovative approach to fuse cells with shorter, nanosecond (ns) pulses. Using numerical calculations we demonstrate that ns pulses can induce selective electroporation of the contact areas between cells (i.e. the target areas), regardless of the cell size. We then confirm experimentally on B16-F1 and CHO cell lines that electrofusion of cells with either equal or different size by using ns pulses is indeed feasible. Based on our results we expect that ns pulses can improve fusion yields in electrofusion of cells with different size, such as myeloma cells and B lymphocytes in hybridoma technology.

  • 38.
    Seifnaraghi, Nima
    et al.
    Middlesex University, UK.
    Tizzard, Andrew
    Middlesex University, UK.
    de Gelidi, Serena
    Middlesex University, UK.
    Khodadad, Davood
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Nordebo, Sven
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Van Kaam, Anton
    University of Amsterdam, The Netherlands.
    Frerichs, Inez
    University Medical Centre Schleswig-Holstein, Germany.
    Waldmann, Andreas
    Swisstom AG company, Switzerland.
    Sorantin, Erich
    Medical University of Graz, Austria.
    Tschauner, Sebastian
    Medical University of Graz, Austria.
    Demosthenous, Andreas
    UCL, UK.
    Christofides, Stelios
    Nicosia General Hospital, Cyprus.
    Bayford, Richard
    Middlesex University, UK.
    Estimation of thorax shape for forward modelling in lungs EIT2017In: Proceedings of the 18th International Conference on Biomedical Applications of Electrical Impedance Tomography / [ed] Alistair Boyle, Ryan Halter, Ethan Murphy & Andy Adler, Hanover, New Hampshire, USA: Thayer School of Engineering at Dartmouth , 2017, p. 58-58Conference paper (Refereed)
    Abstract [en]

    The thorax models for pre-term babies are developed based on the CT scans from new-borns and their effect on image reconstruction is evaluated in comparison with other available models.

  • 39.
    Sjödén, Therese
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
    Nordebo, Sven
    Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
    Nilsson, Börje
    Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
    Sensitivity analysis for inverse problems in Electrical Impedance Tomography2012Conference paper (Refereed)
  • 40.
    Ušaj, Marko
    et al.
    University of Ljubljana, Slovenia.
    Flisar, Karel
    University of Ljubljana, Slovenia.
    Miklavcic, Damijan
    University of Ljubljana, Slovenia.
    Kanduser, Masa
    University of Ljubljana, Slovenia.
    Electrofusion of B16-F1 and CHO cells: the comparison of the pulse first and contact first protocols2013In: Bioelectrochemistry, ISSN 1567-5394, E-ISSN 1878-562X, Vol. 89, p. 34-41Article in journal (Refereed)
    Abstract [en]

    High voltage electric pulses induce permeabilisation (i.e. electroporation) of cell membranes. Electric pulses also induce fusion of cells which are in contact. Contacts between cells can be established before electroporation, in so-called contact first or after electroporation in pulse first protocol. The lowest fusion yield was obtained by pulse first protocol (0.8%±0.3%) and it was only detected by phase contrast microscopy. Higher fusion yield detected by fluorescence microscopy was obtained by contact first protocol. The highest fusion yield (15%) was obtained by modified adherence method whereas fusion yield obtained by dielectrophoresis was lower (4%). The results are in agreement with current understanding of electrofusion process and with existing electrochemical models. Our data indicate that probability of stalk formation leading to fusion pores and cytoplasmic mixing is higher in contact first protocol where cells in contact are exposed to electric pulses. Another contribution of present study is the comparison of two detection methods. Although fusion yield can be more precisely determined with fluorescence microscopy we should note that by using this detection method single coloured fused cells cannot be detected. Therefore low fusion yields are more reliably detected by phase contrast microscopy.

  • 41.
    Ušaj, Marko
    et al.
    University of Ljubljana, Slovenia.
    Kandušer, Maša
    University of Ljubljana, Slovenia.
    Modified Adherence Method (MAM) for Electrofusion of Anchorage-Dependent Cells2015In: Cell Fusion: Overviews and Methods, New York, NY: Humana Press, 2015, p. 203-216Chapter in book (Refereed)
    Abstract [en]

    The artificially induced cell fusion is a useful experimental tool in biology, biotechnology and medicine. The electrofusion is a physical method for cell fusion that applies high-voltage electric pulses. The use of electric pulses causes cell membrane structural changes which bring the cell membrane in the so-called fusogenic state. When such fusogenic membranes are in close contact cell fusion takes place. Physical contact between fusion partners can be achieved by various methods and one of them is modified adherence method (MAM) described in detail here on B16-F1 cell line. The method is based on the fact that living cells form contacts in confluent culture. However, instead of using confluent cell culture, in modified adherence method cells are plated in suitable concentration and allowed to form contacts for only short predetermined period of time. During that time the cells are only slightly attached to the dish surface maintaining the spherical shape. Observed high fusion yields up to 50 % obtained by MAM in situ by dual-color fluorescence microscopy are among the highest in field of electrofusion. The method can be readily adapted to other anchorage-dependent cell lines.

  • 42.
    Y Banaem, Hossein
    et al.
    Tehran University of Medical Science, Iran.
    Ahmadian, Alireza
    Tehran University of Medical Science, Iran.
    Saberi, Hooshangh
    Tehran University of Medical Science, Iran.
    Daneshmehr, Alireza
    University of Tehran, Iran.
    Khodadad, Davood
    Tehran University of Medical Science, Iran.
    Brain tumor modeling: glioma growth and interaction with chemotherapy2011In: International Conference on Graphic and Image Processing (ICGIP 2011) / [ed] Yi Xie, Yanjun Zheng, 2011, article id 82851MConference paper (Refereed)
    Abstract [en]

    In last decade increasingly mathematical models of tumor growths have been studied, particularly on solid tumors which growth mainly caused by cellular proliferation. In this paper we propose a modified model to simulate the growth of gliomas in different stages. Glioma growth is modeled by a reaction-advection-diffusion. We begin with a model of untreated gliomas and continue with models of polyclonal glioma following chemotherapy. From relatively simple assumptions involving homogeneous brain tissue bounded by a few gross anatomical landmarks (ventricles and skull) the models have been expanded to include heterogeneous brain tissue with different motilities of glioma cells in grey and white matter. Tumor growth is characterized by a dangerous change in the control mechanisms, which normally maintain a balance between the rate of proliferation and the rate of apoptosis (controlled cell death). Result shows that this model closes to clinical finding and can simulate brain tumor behavior properly.

  • 43.
    Yousefi, Hossein
    et al.
    Tehran University of Medical Sciences (TUMS), Iran.
    Ahmadian, Alireza
    Tehran University of Medical Sciences (TUMS), Iran.
    Khodadad, Davood
    Luleå University of Technology ; Exceptional Talents Development Centre, Iran.
    Saberi, Hooshangh
    Tehran University of Medical Sciences (TUMS), Iran ; Spinal Injuries Repair Research Centre, Iran.
    Daneshmehr, Alireza
    University of Tehran, Iran.
    An Optimised Linear Mechanical Model for Estimating Brain Shift Caused by Meningioma Tumours2013In: International Journal of Biomedical Science and Engineering, ISSN 2376-7227, Vol. 1, no 1, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Estimation of brain deformation plays an important role in computer-aided therapy and image-guided neurosurgery systems. Tumour growth can cause brain deformation and change stress distribution in the brain. Biomechanical models exist that use a finite element method to estimate brain shift caused by tumour growth. Such models can be categorised as linear and non-linear models, both of which assume finite deformation of the brain after tumour growth. Linear models are easy to implement and fast enough to for applications such as IGS where the time is a great of concern. However their accuracy highly dependent on the parameters of the models in this paper, we proposed an optimisation approach to improve a naive linear model to achieve more precise estimation of brain displacements caused by tumour growth. The optimisation process has improved the accuracy of the model by adapting the brain model parameters according to different tomour sizes.We used patient-based tetrahedron finite element mesh with proper material properties for brain tissue and appropriate boundary conditions in the tumour region. Anatomical landmarks were determined by an expert and were divided into two different sets for evaluation and optimisation. Tetrahedral finite element meshes were used and the model parameters were optimised by minimising the mean square distance between the predicted locations of the anatomical landmarks derived from Brain Atlas images and their actual locations on the tumour images. Our results demonstrate great improvement in the accuracy of an optimised linear mechanical model that achieved an accuracy rate of approximately 92%.

  • 44.
    Yousefi-Banaem, Hossein
    et al.
    Isfahan University of Med. Sci., Iran.
    Kermani, Saeed
    Isfahan University of Med. Sci., Iran.
    Sarrafzadeh, Omid
    Isfahan University of Med. Sci., Iran.
    Khodadad, Davood
    Luleå University of Technology.
    An improved spatial FCM algorithm for cardiac image segmentation2013In: 13th Iranian Conference on Fuzzy Systems (IFSC), 2013, IEEE Press, 2013Conference paper (Refereed)
    Abstract [en]

    Image segmentation is one of challenging field in medical image processing. Segmentation of cardiac wall is one of challenging work and it is very important step in evaluation of heart functionality by existing methods. For cardiac image analysis, Fuzzy C- Means (FCM) algorithm proved to be superior over the other clustering approaches in segmentation field. However, the nave FCM algorithm is sensitive to noise because of not considering the spatial information in the image. In this paper an improved FCM algorithm is formulated by incorporating the spatial domain neighborhood information into the membership function for clustering (ISFCM). In this paper we applied improved Fuzzy c-Means with spatial information for left ventricular wall segmentation. Obtained results showed that the proposed method can segment cardiac wall automatically with acceptable accuracy. The comparison of proposed method with nave FCM proved that ISFCM can segment with more accuracy than nave FCM.

1 - 44 of 44
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