Przeglądaj {{ collection }} wg Autor "Materka, Andrzej"

Teraz wyświetlane 1 - 4 z 4

Computer Simulation of Magnetic Resonance Angiography Imaging: Model Description and Validation
(2014) Klepaczko, Artur; Szczypiński, Piotr M.; Dwojakowski, Grzegorz; Strzelecki, Michał; Materka, Andrzej
With the development of medical imaging modalities and image processing algorithms, there arises a need for methods of their comprehensive quantitative evaluation. In particular, this concerns the algorithms for vessel tracking and segmentation in magnetic resonance angiography images. The problem can be approached by using synthetic images, where true geometry of vessels is known. This paper presents a framework for computer modeling of MRA imaging and the results of its validation. A new model incorporates blood flow simulation within MR signal computation kernel. The proposed solution is unique, especially with respect to the interface between flow and image formation processes. Furthermore it utilizes the concept of particle tracing. The particles reflect the flow of fluid they are immersed in and they are assigned magnetization vectors with temporal evolution controlled by MR physics. Such an approach ensures flexibility as the designed simulator is able to reconstruct flow profiles of any type. The proposed model is validated in a series of experiments with physical and digital flow phantoms. The synthesized 3D images contain various features (including artifacts) characteristic for the time-of-flight protocol and exhibit remarkable correlation with the data acquired in a real MR scanner. The obtained results support the primary goal of the conducted research, i.e. establishing a reference technique for a quantified validation of MR angiography image processing algorithms.
Information technology networked system for student mobility support
(Emerald Group Publishing Limited, 2015) Dębiec, Piotr; Materka, Andrzej
Purpose - This paper presents an IT system - Student Connectivity Module (SCM) - designed for support of administration of student exchange between universities in different countries, developed under the EU 7th Framework Programme. This paper aims to share the acquired knowledge on existing difficulties in mobility management, propose solutions to those problems, and present results of system validation using its prototype deployed at two universities. Design/methodology/approach - Prior to the system design, the needs, plans and expectations concerning the academic IT services were surveyed among 100 universities. On this basis, in close with prospective system users, an original peer-to-peer system was developed using top-down model-driven and agile software development techniques. Findings - The barriers to effective interoperation of academic information systems were revealed: 1) diversity and heterogeneity of campus IT solutions, 2) differences in patterns of international student mobility flow, 3) diversity in national personal data protection policies, 4) lack of standards for e-data exchange. The SCM system overcomes these problems by adopting platform-independent IT solutions, Web-Services, a network of trusted authority servers, and a novel “quasi-standard” solution for e-data exchange, with the use of home university campus cards to access facilities at host institutions. Originality - The management of foreign student exchange is a complicated process. It involves students, faculty, administrative staff and external institutions. To our knowledge, there is no other comprehensive networked IT system available to facilitate administration of student mobility, make it better controlled, less laborious and faster, in a secure way. Our IT solution contributes to overcoming the current barriers to academic mobility within Europe and elsewhere.
Modelowanie i analiza sygnału elektrokardiograficznego z zastosowaniem układów i przekształceń nieliniowych
(Wydawnictwo Politechniki Łódzkiej, 2002) Strumiłło, Paweł; Materka, Andrzej
Zagadnienia referowane w rozprawie dotyczą zastosowań układów i przekształceń nieliniowych, takich jak nieliniowe układy dynamiczne, jednokierunkowe sieci neuronowe i kaskadowe filtry medianowe, do modelowania i analizy sygnału elektrokardiograficznego (EKG). Celem pracy jest wykazanie, że metody przetwarzania nieliniowego i modele nieliniowe istotnie wzbogacają medyczną informację diagnostyczną o tym najczęściej rejestrowanym sygnale elektrofizjologicznym. Pokazano, że koncepcje nieliniowego przetwarzania sygnałów oferują nową jakość, a nawet prostotę analizy niedostępną dla klasycznych układów liniowych. Interpretację elektrokardiogramu jako wyniku rejestracji aktywności nieliniowego układu dynamicznego wykorzystano do opracowania metody detekcji oraz ilościowej oceny zaburzeń repolaryzacji komór serca (tzw. altemansu załamka T). Wykazano, że metoda przecięć Poincare, oparta na teorii nieliniowych układów dynamicznych, wymaga znacznie mniejszych nakładów obliczeniowych niż tradycyjnie stosowana analiza widmowa Fouriera. Zaproponowano nowy sposób reprezentacji altemansu załamka T przez utworzenie dwuwymiarowej, czasowo-przestrzennej reprezentacji zmienności tego załamka (dla odprowadzeń przedsercowych Vl÷V6). Znaczną część pracy poświęcono układom analizy sygnału EKG wywodzącym się z koncepcji sztucznych sieci neuronowych (SSN). Zaproponowano skuteczną metodę budowania „uniwersalnych aproksymatorów neuronowych", która nie wymaga stosowania kosztownych obliczeń iteracyjnych. SSN zastosowano do wspomagania analizy zaburzeń rytmu spowodowanego migotaniem przedsionków serca ( ekstrapolacja odcinków sygnału EKG po uprzednim usunięciu zespołów QRS) oraz zbudowania modelu aproksymacyjnego sygnału wykorzystującego ideę adaptacyjnego dopasowania funkcji bazowych. Ostania część pracy dotyczy nieliniowej dekompozycji wielorozdzielczej sygnału EKG polegającej na kaskadowej filtracji medianowej (tzw. sita filtrów medianowych). W wyniku zastosowania tego dwuwymiarowego zobrazowania sygnału osiągnięto dużą dokładność detekcji chwil zakończenia załamka T, pokazano też nowe możliwości tej transformacji, użyteczne w wykrywaniu innych charakterystycznych cech sygnału EKG oraz ważnych arytmii serca.
Signals and systems
(Lodz University of Technology. Press, 2004) Tadeusiewicz, Michał; Wojciechowski, Jacek; Materka, Andrzej
This book gives an introductory treatment of signals and systems and is intended to be used as a text for students of electrical and electronic engineering. It is based on the experience of teaching circuits, signals and systems at the Faculty of Electrical and Electronic Engineering as well as the International Faculty of Engineering of the Technical University of Lodi. It is assumed that the reader has some knowledge of complex numbers and functions, basic electrical engineering and circuit theory. These prerequisite skills are mastered by the students during the junior years. The book should also be useful to engineers, enabling them to update and enhance their knowledge of signals and systems through self-study. Since the book is addressed to the electrical and electronic engineering students the material contains, beside the standard subjects of signals and systems, also analog-filter and digital-filter design. For the same reason numerous examples used to illustrate the theoretical material ref er to electric and electronic circuits and systems. The book includes a large number of examples. They are provided to illustrate the concepts and to make the theory more understandable. Furthermore, the examples enable the students to master some techniques and analysis tools and learn to use them effectively. Throughout the book linear, time-invariant systems are studied and continuous-time as well as discrete-time signals and systems are considered simultaneously as much as possible. The book provides the fundamentals of signals and systems and gives a background for later signal processing studies. A brief outline of this material is as follows. Chapter I presents an introduction to continuous-time and discrete-time signals and systems. It provides preliminary concept, basic definitions, and mathematical techniques including the continuous and discrete convolution. Chapter 2 is devoted to the Laplace transform and its application to circuit analysis. It examines in detail basic properties, rules, and techniques of the Laplace transform and derives the operator method for the analysis of linear circuits and systems. The results of Chapter 2 are extended in Chapter 3 where the concept of transfer function of continuous systems is introduced and block diagrams and signal-flow graphs enabling to determine transfer functions are discussed. Starting from Chapter 4 we consider frequency-domain descriptions of signals. Fourier series representation for continuous-time signals is included in Chapter 4. Chapter 5 exploits Fourier series to the analysis of systems driven by periodic excitations. The discrete Fourier series is introduced in Chapter 6. Discrete Fourier transform is developed in Chapter 7 and its effective implementation, known as the fast Fourier transform, is discussed in Chapter 8. Chapter 9 presents in detail the Fourier transform of continuous-time signals whereas Chapter 10 deals with the Fourier transform of discrete-time signals. Some applications of the Fourier transform, including sampling of continuoustime signals, and amplitude modulation, are given in Chapter 11. The concepts of signal energy and power are developed in Chapter 12. Chapter 13 is devoted to the Z-transform of discrete-time signals; it discusses basic properties and introduces the transfer function of a discrete system. The final two chapters are focused on design of analog and digital filters. Both mathematical background and some techniques of design of the analog Butterworth and the Chebyshev filters are developed in Chapter 14. The design techniques of digital filters are presented in Chapter 15. Window approach for designing FIR filters is discussed and bilinear transformation as well as the impulse-invariance technique for designing IIR filters are developed.[...]