1,721,049 research outputs found
Modelli computazionali della biomeccanica cellulare
No full textThe understanding of the human body mechanobiology has greatly increased over the years leading to better health outcomes in many medical fields. The powerful tools provided by methods such as finite element analysis have been proven effective in investigating, diagnosing and curing pathologies while also providing a framework which is cheap, reproducible and customisable. The field of cellular biomechanics can greatly benefit from these tools thanks to their ability to be adapted to the investigator's needs thus allowing testing setups which would not be possible otherwise and that would more closely reproduce the in vivo conditions of interest. For these reasons, this dissertation presents relevant advancements in the type and complexity of finite element models for the investigation of both healthy and pathological cells with a focus on cancerous cells. The purely mechanical models presented use the concepts of tensegrity and bendo-tensegrity to create models which can reproduce the mechanical response of a cell undergoing micropipette aspiration or atomic force indentation while increasing the level of accuracy and complexity achieved by the classical homogeneous models present in the literature. The biomechanical models developed for this work show the potential of finite element models in bridging our understanding of cell physiology and cell biomechanics. These models have shown great potential in describing the response of the cell to both physical conditions (such as osmotic pressure fields) and mechanical stresses. Taken together, these two classes of models can greatly contribute to our understanding of the complex life of cells both from a biological and mechanical standpoint thus allowing us to take a first step in bridging these two fields
EPTlib: An Open-Source Extensible Collection of Electric Properties Tomography Techniques
Full text linkElectric properties tomography (EPT) is a novel magnetic resonance imaging–based method to estimate non-invasively the distribution of the electric properties in the human body. In this paper, EPTlib, an open-source extensible C++ library collecting ready-to-use algorithms for electric properties tomography, is presented. Currently, EPTlib implements three techniques, named Helmholtz-EPT, convection-reaction-EPT and gradient-EPT, whose derivation and implementation is deeply discussed. Moreover, the configuration files needed by the terminal application included in EPTlib to apply the implemented techniques are outlined. The three techniques are applied to a couple of model problems in order to highlight their main features and the effects of the tunable parameters
Mathematical methods for magnetic resonance based electric properties tomography
Full text linkMagnetic resonance-based electric properties tomography (MREPT) is a recent quantitative imaging technique that could provide useful additional information to the results of magnetic resonance imaging (MRI) examinations. Precisely, MREPT is a collective name that gathers all the techniques that elaborate the radiofrequency (RF) magnetic field B1 generated and measured by a MRI scanner in order to map the electric properties inside a human body. The range of uses of MREPT in clinical oncology, patient-specific treatment planning and MRI safety motivates the increasing scientific interest in its development. The main advantage of MREPT with respect to other techniques for electric properties imaging is the knowledge of the input field inside the examined body, which guarantees the possibility of achieving high-resolution. On the other hand, MREPT techniques rely on just the incomplete information that MRI scanners can measure of the RF magnetic field, typically limited to the transmit sensitivity B1+. In this thesis, the state of art is described in detail by analysing the whole bibliography of MREPT, started few years ago but already rich of contents. With reference to the advantages and drawbacks of each technique proposed for MREPT, the particular implementation based on the contrast source inversion method is selected as the most promising approach for MRI safety applications and is denoted by the symbol csiEPT. Motivated by this observation, a substantial part of the thesis is devoted to a thoroughly study of csiEPT. Precisely, a generalised framework based on a functional point of view is proposed for its implementation. In this way, it is possible to adapt csiEPT to various physical situations. In particular, an original formulation, specifically developed to take into account the effects of the conductive shield always employed in RF coils, shows how an accurate modelling of the measurement system leads to more precise estimations of the electric properties. In addition, a preliminary study for the uncertainty assessment of csiEPT, an imperative requirement in order to make the method reliable for in vivo applications, is performed. The uncertainty propagation through csiEPT is studied using the Monte Carlo method as prescribed by the Supplement 1 to GUM (Guide to the expression of Uncertainty in Measurement). The robustness of the method when measurements are performed by multi-channel TEM coils for parallel transmission confirms the eligibility of csiEPT for MRI safety applications
Mathematical modeling for the design of evolution experiments to study the genetic instability of metabolically engineered photosynthetic microorganisms
Full text linkEngineering the metabolism of photosynthetic microorganisms with the aim of converting CO2 and water, by exploiting solar energy, into end-products of commercial value is a rising interest in the biotechnology field. The producing host that carries a genetic modification not associated with competitive fitness advantage usually experiences a production burden (i.e., a metabolic burden related to product synthesis), leading to genetic instability and abortive production phenotype. The genetic instability of these engineered strains is a major hindrance to the spreading of large-scale photosynthetic cell factory processes. This genetic instability can be studied by means of evolution experiments, which are often time-consuming. In these experiments, the cell population is subjected to a long-term culturing during which the possible variation of the number of producers and of cells that lose the production traits, here defined as retro-mutants, is recorded. Here, a mathematical model that describes the dynamics of retro-mutants into a population of metabolically engineered photosynthetic microorganisms has been developed. The model has been used to simulate evolution experiments, conducted both in continuous (chemostat and turbidostat) and semi-continuous (serial batch transfer) culturing modes. These simulations allowed identifying the set of operative parameters for each cultivation mode that optimizes an evolution experiment in terms of experimental time needed to detect the arising of retro-mutants. Moreover, it has been found that in a scale of number of microbial generations only two parameters, precisely the production burden and the mutation rate, are determinant for the appearance of retro-mutants. These parameters are intrinsic features of any metabolically engineered strain and do not depend on the adopted cultivation system or on the microbial growth kinetics characteristics. This result further extends the applicability of the model also to non-photosynthetic metabolically engineered microorganisms
GPU-Accelerated Finite Element and Finite Difference Methods for Scattering Problems in Voxelbased Human Models
No full textComputational Low-Frequency Electromagnetic Dosimetry Based on Magnetic Field Measurements
Full text linkThis paper compares different experimental-computational strategies for the estimation of electric fields induced in human bodies by low-frequency magnetic sources characterized by a set of magnetic field measurements. The analysis is carried out by considering three alternative procedures, which use, as the first input, the distribution of the magnetic flux density in a volume containing the studied body or on a surface surrounding the sources. The comparison is performed on a realistic model problem, related to transcranial magnetic stimulation (TMS), in which numerically simulated “virtual measurements” are employed. The comparative analysis is developed in terms of both result accuracy and robustness against noisy input due to unavoidable experimental uncertainties. It results that by performing the measurements on a surface surrounding the sources, a significant reduction of the experimental burden is found with respect to the case of volume measurements, affecting neither the accuracy nor the robustness of the procedure. In particular, when whole body electric field evaluation must be carried out, the advantage of surface measurements with respect to volume ones becomes significant. Moreover, a preferable scheme obtained as hybridization of previously proposed strategies is identified. Besides the adoption of a TMS model problem in the comparison procedure, the achieved result can be extended to any low-frequency dosimetric assessments, where the magnetic sources are difficult to model or not completely known
A fast tool for the parametric analysis of human body exposed to LF electromagnetic fields in biomedical applications
Full text link: A numerical procedure for analyzing electromagnetic (EM) fields interactions with biological tissues is presented. The proposed approach aims at drastically reducing the computational burden required by the repeated solution of large scale problems involving the interaction of the human body with EM fields, such as in the study of the time evolution of EM fields, uncertainty quantification, and inverse problems. The proposed volume integral equation (VIE), focused on low frequency applications, is a system of integral equations in terms of current density and scalar potential in the biological tissues excited by EM fields and/or electrodes connected to the human body. The proposed formulation requires the voxelization of the human body and takes advantage of the regularity of such discretization by speeding-up the computational procedure. Moreover, it exploits recent advancements in the solution of VIE by means of iterative preconditioned solvers and ad hoc parametric Model Order Reduction techniques. The efficiency of the proposed tool is demonstrated by applying it to a couple of realistic model problems: the assessment of the peripheral nerve stimulation, performed in terms of evaluation of the induced electric field, due to the gradient coils of a magnetic resonance imaging scanner during a clinical examination and the assessment of the exposure to environmental fields at 50 Hz of live-line workers with uncertain properties of the biological tissues. Thanks to the proposed method, uncertainty quantification analyses and time domain simulations are possible even for large scale problems and they can be performed on standard computers and reasonable computation time. Sample implementation of the method is made publicly available at https://github.com/UniPD-DII-ETCOMP/BioMOR
A Model to Analyze the Skin Heating Produced by Millimeter and Submillimeter Electromagnetic Waves
No full text- …
