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Mapping and homogenity correction of basic magnetic field in tomograph
Žůrek, Dalibor ; Kubásek, Radek (referee) ; Hadinec, Michal (advisor)
This work focuses on a search of available literature in the field of mapping the magnetic field and the degradation of the field gradients. Initially on introduction to basic concepts in the field of magnetic resonance imaging, which are important for understanding the problems and become familiar with the principles of measurement of magnetic fields on the selected surface. Furthermore, there are described two basic measurement techniques, magnetic resonance imaging. The work is analyzed the degradation patterns of magnetic field gradients using the Taylor series and spherical functions. The second part describes how to obtain readings in the tomograph, which together with the previous decomposition of the field then used to describe a numerical calculation of magnetic induction on the surface of a sphere. Values measured and calculated values are compared at the end.
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The Noise Spectroscopy of Radiation Detectors Based on the CdTe
Zajaček, Jiří ; Štourač, Ladislav (referee) ; Hájek, Karel (referee) ; Grmela, Lubomír (advisor)
The main object of this work is noise spectroscopy of CdTe radiation detectors (-rays and X–rays) and CdTe samples. The study of stochastic phenomenon and tracing redundant low-frequency noise in semiconductor materials require long-term measurements in time domain and evaluate suitable power spectral densities (PSD) with logarithmic divided frequency axes. We have used the means of time-frequency analysis derived from the discrete wavelet transform (DWT) and we have designed the effective algorithm for PSD estimation, which is comparable with an original analog method. CdTe single crystal with Au contacts we can imagine as a series connection of two Schottky diodes with a resistor between them. The bulk resistance at constant temperature and other constant parameters changes due to the carrier concentration changing only. The p-type CdTe sample shows metal behavior with every temperature changes. Semiconductor properties of the sample begin to dominate just after some period of time. This behavior is caused by the hole mobility changing. The voltage noise spectral density of 1/f noise depends on the quantity of free carriers in the sample. All the studied samples have very high value of low frequency noise, much higher than it should have been according to Hooge’s formula. The excess value of low frequency noise is caused by the low carrier concentration within the depleted region.
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Study of the properties of hyperpolarized xenon-129 for magnetic resonance imaging
Rychnovský, Jan ; Nováková,, Sabina (referee) ; Kohout,, jJaroslav (referee) ; Bartušek, Karel (advisor)
Produkce hyperpolarizovaných plynů, především helia (3He) nebo xenonu (129Xe), nachází stále rostoucí rozsah aplikací v zobrazování magnetickou rezonancí (MRI). Helium ani xenon nejsou obyčejně obsaženy v těle a experimenty tedy nejsou ovlivněny nechtěným signálem z okolních tkání. Ukázalo se, že několika hyperpolarizačními technikami může být magnetická polarizace (magnetizace) jader vzácných plynů zvýšena na hladinu, se kterou jsou praktické aplikace proveditelné. Hyperpolarizované plyny mohou tedy být užitečným nástrojem pro neinvazivní zkoumání lidského dýchání, dovolující statické zobrazování během zadržení dechu nebo zkoumání dynamiky výdechu nebo nádechu, nebo funkčního zobrazování. V neživé přírodě, mohou být hyperpolarizovaný plyny využity jako kontrastní látka při studiu mikroporézních materiálů, jako jsou zeolity, stavební látky a hmoty, atd. V této doktorské práci je popsán vývoj a konstrukce aparatury pro hyperpolarizaci xenonu (izotopu 129Xe). Nákup hyperpolarizovaného xenonu od jiných výzkumných center v zahraničí a jeho dovážení by ovšem nebylo efektivní a to zejména z důvodu náročnosti zajištění potřebných fyzikálních podmínek pro přepravu hyperpolarizovaného plynu. Toto bylo hlavní motivací k vývoji vlastní technologie pro přípravu hyperpolarizovaného xenonu. Se zvládnutou technologií by bylo možné navázat spolupráci s medicínskými zařízeními, nebo s týmy zabývající se živou nebo neživou přírodou (např. při studiu mikroporézních materiálů, gelů, v zemědělských aplikacích nebo při výzkumu využívajících zvířat, atd.). Cílem této práce je studium teorie hyperpolarizovaných vzácných plynů se zaměřením na 129Xe a experimentální ověření a změření relaxačních časů pomocí jaderné magnetické rezonance. Vzhledem k tomu, že je možné hyperpolarizované vzácné plyny skladovat pro pozdější využití, se tato práce také zabývá možnostmi zásobníku hyperpolarizovaného vzácného plynu a jeho teoretickým a experimentálním řešením. V této práci jsou popsány především dva základní typy experimentů přípravy hyperpolarizovaného xenonu. V obou jsou využity zatavené válcové skleněné vzorky naplněné xenonem a doplňujícím plynem – dusíkem, heliem. První z experimentů se zabývá měřením vlastností termálně polarizovaného xenonu a druhý měřením vlastností hyperpolarizovaného xenonu. Pro hyperpolarizaci 129Xe bylo použito výkonového laseru a experimentálně byla zkoumána jednak míra polarizace na základě změny spektrální hustoty čerpacího laserového svazku a dále pak optimální doba optického čerpání 129Xe a relaxační časy xenonu.
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Study of gel electrolytes properties by MR methods
Mrnka, Michal ; Gescheidtová, Eva (referee) ; Bartušek, Karel (advisor)
Theoretical part of the work deals with explanation of nuclear magnetic resonance phenomenon, relaxation processes in system of nuclear spins, basic techniques for measurement of relaxation times. There are described diffusion and techniques for diffusion coefficient measurement including method for suppressing the background gradient. Experimental part describes preparation of gel electrolytes samples and measurement of relaxation times. Sodium salt was used as a conductive agent. There is interpreted dependence of relaxation times on polymerization times and on concentration of conductive agent in gels.
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Measurement of selected samples relaxations by use of NMR
Kovalčík, Tomáš ; Gescheidtová, Eva (referee) ; Bartušek, Karel (advisor)
The work deals with nuclear magnetic resonance and principles of relaxation measurement and diffusion constants. Magnetic resonance is phenomenon, when energy in the form of RF pulse with Larmor frequency is added to this material in the magnetic field B0, the elements will be excited to a higher energy level. When you measure FID up to 90° RF pulse, from the absorption line, you will acquire . Further we can, for measurement of the transverse relaxation time T2, use the Spin echo method, that makes use of the 90° RF pulse and the series of 180° RF pulses. From measured values, the T2 relaxation time is directly acquired (inhomogeneity will prevent existence).
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MRI Acquisition and Preprocessing of Image Sequences for Clinical Perfusion Imaging
Krchňavý, Jan ; Bartoš, Michal (referee) ; Jiřík, Radovan (advisor)
This thesis describes the theory for static and dynamic magnetic-resonance imaging using contrast agents affecting T1 relaxation time. The available acquisition methods in the specified facility of Masaryk Oncological Institute in Brno are described. The sequences for subsequent experimental measurements are selected. The used phantoms are described. Acquisition protocol for measuring is described briefly and the evaluation method for the measured data is suggested. The best acquisition sequence and a method of measurements is chosen influenced by estimation of relaxation time T1, sensitivity and signal to noise ratio. Perfusion analysis is executed and perfusion parameters are calculated. The work was supported by the European Regional Development Fund and the State Budget of the Czech Republic (RECAMO, CZ.1.05/2.1.00/03.0101).
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MR image data processing in study of tissue cultures
Bidman, Petr ; Šmirg, Ondřej (referee) ; Gescheidtová, Eva (advisor)
Techniques based on principle of nuclear magnetic resonance (NMR) belong to the most modern methods for studying physical, chemical and biological properties of materials [1]. Their universality predestinates them for application in a wide range of scientific disciplines, e.g. in medicine to study properties of tissues. Advantages of techniques utilizing principle of NMR consist in their noninvasiveness and thoughtfulness to human health or studied material. In addition, no undesirable effects of magnetic force field have been so far proved by research. Objectives of this Diploma Thesis are evaluation of MR images of tissue cultures and determination of protons amount included in them. Theoretic part of the Thesis is devoted to the bases of NMR and provides basic overview of MR methods. The spin echo method (SE) is described in more details, including the process of assessment of technique’s parameters, e.g. general magnetization. Practical part of Diploma Thesis is focused on determination of integral of image intensity of clusters of early somatic embryos. Intensity integrals characterizing number of protons in growing cluster were calculated from MR images of spruce embryos contaminated by lead. The intensity of an image weighted by spin density is proportionate to the number of proton nuclei in the chosen slice. The Thesis describes further evaluation of relaxation time T2 from MR images weighted by spin density. Following part is dealing with determination of diffusion from MR images with application of compensation methods, three-measurement arrangement and presentation of obtained results. Images were processed by use of MATLAB and MAREVISI programs.
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Properties of thermo-visco-elastic material 42-809 for vibro-damping segment production
Svoboda, J. ; Pešek, Luděk ; Frölich, V. ; Klášterka, Petr
The mechanical properties of rubber elements made of thermo-visco-elastic material 42 -809 at low temperatures are summarized in the report. The tests were performed in a climate chamber bought by company INOVA Prague. The chamber was built in a fatigue machine INSTRON 8502 and the temperature range is from -50 up to 180 C. For improvement of a measurement accuracy and loading the force cell with a range up to 40kN was installed. The original sample fixtures of the machine were substituted by two rods ending by supporting plate. The rods went through the bottom and top lids of the chamber. The results of static and dynamic characteristics for temperature from -50 to 0 C, measurement of residual deformation and relaxation time, evaluation of a cyclic loading influence on static characteristics and life-time characteristics for lower temperature are herein presented.
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Měření relaxačních časů sodíkových iontů metodami magnetické resonance
Mikotová, E. ; Bartušek, Karel ; Gescheidtová, E.
Nuclear Magnetic Resonance (NMR) experiments enable describing of the structure and the internal mobility of a wide spectrum of materials and systems from solutions, very soft and movable gels over synthetic polymers to organic and inorganic crystals and very hard rigid glass. The paper deals with a study of the relaxation times of the nearly liquid and gel electrolytes with content of natrium ions by the NMR technique. Newly designed method of solid electrolytes samples compounding and a suitable method for measurement of the relaxation times during the samples solidification were established.
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