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Model Study of Ultrasound Effects on Fetal Development
Jaroš, Josef ; Halámek, Josef (referee) ; Hrazdíra,, Ivo (referee) ; Rozman, Jiří (advisor)
The progress in ultrasound techniques goes hand in hand with increasing of diagnostic machine acoustic outputs. Ultrasound biological effects can adversely influence the development of human fetus. Recent studies of thermal effect on biological tissues are usually based on simulation of simple ultrasound transducers. The aim of this work is to build a flexible model of diagnostic system to simulate temperature increase during fetal development. Different types of ultrasound probes were used for generation of acoustic field with simulated piezoelectric element properties. Optimized linear and phased arrays were modeled with dynamic beam steering and focus. Computer simulations were concentrated on extreme conditions in obstetric ultrasonography and 3D tissue model was compared with real ultrasound probes measurements. To detect temperature increase, the bone tissue phantom was used. Results point out potential risks for fetus with diagnostic ultrasound probes. Based on the results of this work, practical recommendations increasing safety of obstetric examinations were drawn.
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Analysis of Nonlinear Effects in Ultrasound Diagnostics
Čížek, Martin ; Hrazdíra,, Ivo (referee) ; Halámek, Josef (referee) ; Rozman, Jiří (advisor)
The model study of nonlinear effects in the ultrasound diagnostics is focused on developing and experimental verification of new computer algorithms for numerical modeling of the ultrasound field including nonlinear effects accompanying the ultrasound propagation in biological tissues. A theoretical analysis of nonlinearities in ultrasound propagation and their contribution to thermal and mechanical effects of diagnostic ultrasound applications was conducted. A numeric model of ultrasound propagating through a tissue model formed of a set of homogenous layers with defined physical parameters was developed in Matlab environment. The computation of ultrasound field spatial distribution is based on the angular spectrum method. For simulating of nonlinearities Burgers nonlinear wave equation is used. The resulting spatial distribution of the ultrasound field is described by the amplitudes of selected number of harmonic components of the acoustic pressure, by the mechanical index, by the harmonic distortion of the signal and by the spatial peak temporal average intensity of all considered components. The numerical model was experimentally verified using an unique ultrasound measurement system – the ultrasound measurement basin. The verified numeric model was used for assessing the veracity of mechanical index and tissue heating prediction during ultrasound applications in cases when the nonlinear effects are neglected in computations. The reliability of the mechanical index indicated by the diagnostic ultrasound instruments is also evaluated using the designed numeric model. The aim was to compare the indicated value usually obtained by derating the measurements in a water medium to the actual mechanical index present in the insonated tissue.
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Detection of the repolarization parameters from ECG
Brandejs, Jakub ; Halámek, Josef (referee) ; Veselý, Petr (advisor)
A T wave peak and offset detector based on an unpublished lead transformation that can be briefly described as multilead linear regression was proposed and implemented afterwards. Potential of the transformation as a useful QRS detection tool was revealed later on. Proposed QRS detector was put to the test of CSE database. Results were compared with work of other authors. Results of T wave peak and offset detector were introduced in visual way.
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Properties of pulse wave velocity in human body during various excitations
Matejková, Magdaléna ; Halámek, Josef (referee) ; Vondra, Vlastimil (advisor)
The thesis is concerned with the analysis of measuring pulse wave velocity in human body with the aid of whole-body multichannel bioimpedance which was developed at ISI AS CR, v.v.i.. The evaluation of pulse wave velocity can provide us with important information about the state of vessel compliance which is one of the basic parameters informing on their physiological state. The examination of the state of vascular system is a very important part of early diagnostics because its pathological states are the main contributor to the rise of cardiovascular diseases and disease mortality. The thesis is concerned with the theoretical analysis together with the available methods of valuation of the state of vascular system that use measuring of pulse wave velocity. The main part of the thesis deals with the analysis of the whole-body multichannel bioimpedance measurement. The proposed and programmed protocol that summarizes and visualizes all obtained information is a part of this thesis. This is currently used as an output of the experimental measurement by this method. Data file for statistical processing contains the values of the pulse wave velocity of 35 healthy volunteers and subsequently the properties of pulse wave are assessed at various excitations.
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SMV-2012-22: Data processing in cardiology
Jurák, Pavel ; Halámek, Josef ; Vondra, Vlastimil
Contracted research has been focused on data processing in cardiology. It includes specialized analyzes of large polysomnographic records mainly from long-term sleep studies. Research involves advanced techniques for detection and analysis of heart rate, heart depolarization and repolarization and hemodynamic changes during different sleep stages. Detected numerical parameters were further processed and analyzes by different statistical methods
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The voltammetric analysis based on electrolyte signal
Holík, M. ; Halámek, Josef ; Mikelová, R. ; Trnková, L.
The voltammetric measurements of Hetero-oligodeoxynucleotides ODNs: 5´-CCC AAA CCC- 3´, 5´-CAC CACCAC- 3´, and 5´-ACC CAC CCA- 3´ on AUTOLAB 20 (EcoChemie, The Netherlands) were analyzed with different baseline correction - linear, exponential, polynomial and with shape defined by signal of electrolyte. The best results were achieved with correction based on electrolyte and exponential shape.
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Dvoukanálový, komplexní, bioimpedanční signál pro vyhodnocení hemodynamiky
Halámek, Josef ; Vondra, Vlastimil ; Jurák, Pavel ; Verner, Petr
The complex bioimpedance signals measured in the aortal and pulmonary artery directions simultaneously are discussed with respect to the information about the heart activity. All four signals carry some information about the blood flow, this information is partly equivalent (only SNR improvement and some artefact minimizations may be achieved by processing all signals) and partly non-equivalent (different behaviour according to excitation of the cardiovascular system). The more detailed analysis of time evolution of signal parameters according to the used excitation may contribute to new information about the hemodynamic system.
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Evaluation of cognitive ERP, ERD/ERS from intracerebral electrodes during the testing of executive functions, the time – frequency analysis
Chládek, Jan ; Bočková, M. ; Halámek, Josef ; Jurák, Pavel ; Nestrašil, I. ; Rektor, I.
In the present paper we describe the procedure of evaluation repeated EEG signals obtained from deep brain structures. Data are processed using the time-frequency analysis, which helps to determine individual frequency (IF) bands and afterwards are processed using complex demodulation technique to assess power envelope of IF band. We analysed phase-locked (Event-Related Potentials) and non-phase-locked (Event Related De/Synchronisation) signals obtained during different task conditions. Because of low signal to noise ratio, statistical tests of credibility and significance were used.
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