National Repository of Grey Literature 157 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Numerical Modeling of Periodical Structures
Nešpor, Dušan ; Bartušek, Karel (referee) ; Brančík, Lubomír (referee) ; Fiala, Pavel (advisor)
The thesis discusses the dynamic electromagnetic field on periodic structures. The author focuses on three principal types of resonant structures, considering their application possibilities. In general, these types can be individually defined as follows: materials exhibiting a negative refractive index of the incident electromagnetic wave; structures with gradual changes in impedance, characterised by their usability as reflectionless surfaces; and periodic structures able to conveniently shape the magnetic field distribution. Materials of the third group within the above-shown short list facilitate the fabrication of magnetoinductive lenses for nuclear magnetic resonance. The presented analysis of the properties of periodic resonant structures is mainly based on numerical models utilising the finite element method, and this approach is combined with both the derivation of the corresponding analytical relations and an experimental measurement of the non-radiating component of the electromagnetic field. The thesis includes a physical description of the basic elements of periodic resonant structures. Physical properties of the elements were examined in detail via numerical analysis. In the course of the research, the data acquired through this analysis and the related experimental measurement enabled the author to propose a method for optimising the most widely used resonant structures. Moreover, several new versions of resonant elements, structures, and fabrication techniques were also designed. The results obtained from the numerical analyses carried out to examine the central physical properties of the fabricated structure samples were all verified via the designed method for measuring the non-radiating component of the magnetic field.
Creating 3D Model of Temporomandibular Joint
Šmirg, Ondřej ; Bartušek, Karel (referee) ; Liberda,, Ondřej (referee) ; Smékal, Zdeněk (advisor)
The dissertation thesis deals with 3D reconstruction of the temporomandibular joint from 2D slices of tissue obtained by magnetic resonance. The current practice uses 2D MRI slices in diagnosing. 3D models have many advantages for the diagnosis, which are based on the knowledge of spatial information. Contemporary medicine uses 3D models of tissues, but with the temporomandibular joint tissues there is a problem with segmenting the articular disc. This small tissue, which has a low contrast and very similar statistical characteristics to its neighborhood, is very complicated to segment. For the segmentation of the articular disk new methods were developed based on the knowledge of the anatomy of the joint area of the disk and on the genetic-algorithm-based statistics. A set of 2D slices has different resolutions in the x-, y- and z-axes. An up-sampling algorithm, which seeks to preserve the shape properties of the tissue was developed to unify the resolutions in the axes. In the last phase of creating 3D models standard methods were used, but these methods for smoothing and decimating have different settings (number of polygons in the model, the number of iterations of the algorithm). As the aim of this thesis is to obtain the most precise model possible of the real tissue, it was necessary to establish an objective method by which it would be possible to set the algorithms so as to achieve the best compromise between the distortion and the model credibility achieve.
Measurement of small objects by magnetic resonance
Chotaš, Kryštof ; Bartušek, Karel (referee) ; Klusáček, Stanislav (advisor)
Bachelor thesis deals with the issue of noise reduction in magnetic resonance imaging. In this thesis we discuss about suitable methods of noise reduction for images obtained by magnetic resonance tomography. Including classical methods we also discuss noise suppression by getting fewer slices than in ordinary situation. Then we would obtain remaining slices by interpolation. This thesis also include comparison of application of these methods. This thesis also deals with the issue of magnetic resonance, which is described in first chapter.
Optimization of Basic Magnetic Field Homogeneity in MR Tomography
Hadinec, Michal ; Brančík, Lubomír (referee) ; Frollo, Ivan (referee) ; Bartušek, Karel (advisor)
This thesis is concerned with problems of measuring and mapping of magnetic field in MR tomograph, for purpose of magnetic flux density homogeneity optimization. Attention is paid to mapping techniques on rotary symmetric volume and to ways of magnetic fields optimization with utilization of passive and active correction systems. Theoretical analysis of magnetic field decomposition with utilization of spherical harmonics and numerical decomposition is made. Mapping and approximation techniques of basic magnetic field are verified by experiments in the laboratory at the Institute of Scientific Instruments AS CR in Brno.
Study of the influence of magnetic fields on biological tissue
Vlachová Hutová, Eliška ; Fiala, Pavel (referee) ; Bartušek, Karel (advisor)
The aim of this research is to explore the influence of magnetic field on early somatic embryos (ESEs) of spruce and pine. The magnetic field is gradual. This is important for the experiment, each cluster of ESE was exposed to magnetic field of different intensity. The resulting report of this experiment consists of the comparison between various methods of image analysis and the difference in growth of ESEs due to different exposure to magnetic field and surrounding temperature. Enclosed is a proposal of ESE size computing algorithm from a given image.
Diffussion measurement by NMR
Vanko, Filip ; Gescheidtová, Eva (referee) ; Bartušek, Karel (advisor)
In Bachelor thesis is described the principle of MRI, the physical foundations of the phenomenon of magnetic resonance imaging, quantum and macroscopic model. Followed by a description of the mechanisms of relaxation of magnetic resonance phenomenon. In the following sections describes the basis of diffusion, each sequence for measuring diffusion NMR methods and the method of three measurements, which was used in experimental measurements. Last chapter deals with the practical. The results of measurements are evaluated in conclusion.
Susceptibility weighted magnetic resonance imaging (SWI)
Bačovský, Jaromír ; Bartušek, Karel (referee) ; Starčuk, Zenon (advisor)
Susceptibility weighted magnetic resonance imaging (SWI) seems to be a very promising method usable in the diagnosis of a number of clinical and biomedical applications. Difusse axonal injuries and neurodegenerative diseases to name a few. The goal of my bachelor's thesis was to study the principal methods of magnetic resonance imaging with particular emphasis on susceptibility weighted imaging. Then use this theoretical knowledge for practical implementation of the SWI method to 4,7T/200mm NMR system located at Institute of Scientific Instruments of the ASCR, v.v.i. It was necessary to create an image calculated software, which is capable of enhancing contrast caused by magnetic susceptibility differences as they manifest themselves in local phase changes between tissues. Few basic problems had to be solved. The phase image was filtered by a high pass filter, a Phase Mask was created from adjusted image, which is generated from phase unwrapped image. To varify the SWI method, samples were designed, which have the desired magnetic properties. During the initial phase of experimenting, hen's eggs were used and then citrus fruits with nanoiron, CaCl2, Zn and AgCl. We investigated basic parametres and settings of the MRI measurements that affect final susceptibility weighted image.
Minimization number of measured data for magnetostatic field mapping
Csonka, Gábor ; Bartušek, Karel (referee) ; Dědková, Jarmila (advisor)
This work deals with questions of mapping statical magnetical field and methods analyses plumbed dates. There is mentioned solving of problems and interpretation of results. Work is centered on evaluation map of magnetic field in workspace of MR tomography from data measured on surface shere. Imposition of submission is proposition acceptable mathematical method and trought program MATLAB compile algorithm for interpretation map magnetic field. In work is further included calculation resulting values of coefficients for induction of magnetic field for selected parts of sphere. By force of admeasurement were experimentally verifyded values wich from the work proceed. Designed method is possible to use for calculation of coefficeints for magnetic induction at any point on sphere from booked up dates.
Analysis and segmentation of tomographic images
Dorazil, Jan ; Bartušek, Karel (referee) ; Smékal, Zdeněk (advisor)
The thesis deals with the edge detection in the magnetic resonance images and their segmentation. There are adduced the gradient based methods, methods based on zero-crossing in the Laplacian images and also methods combined both of the methods adduced above. These methods are compared to find the best one for the temporo-mandibular joint detection. Consequently sufficient segmentation method for particular parts of the temporo-mandibular joint (the condyle, the acetabulum and the articular disk) separation is chosen.
Measurement of diffusion coefitients by use of magnetic resonance
Král, Jakub ; Gescheidtová, Eva (referee) ; Bartušek, Karel (advisor)
This Bachelor thesis is focused on imaging techniques based on the principles of nuclear-magnetic resonance. These techniques are one of the most modern studies of physical, chemical and biological properties of substances. Introduction of this work is focused primarily on physical principles. Further in this work attention is given to the method of the PFG-SE but also to more modern multiinterval NMR methods, which removes the systematic measurement errors for heterogeneous materials. Part of the work is also devoted to b-factor calculations for various kinds of pulse sequences. In last part the work is devoted to data processing in Matlab and Marevisi. Selected method from the beginning of the work is than used to measure the diffusion and processing of tissue cultures.

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