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Wyszukujesz frazę "Lewandowski, J" wg kryterium: Autor


Wyświetlanie 1-6 z 6
Tytuł:
Cumulative method of the image reconstruction in synthetic aperture. Experimental results
Autorzy:
Wójcik, J.
Trots, I.
Lewandowski, M.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/331922.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
An analytical model of imaging using synthetic aperture (SA) methods is presented. This model takes into account: fundamental features of an environment, of an electric transmission/reception path and a description of SA structure – possible schemes of transmission, reception and image formation. Then two schemes are analyzed: a proposed cumulative synthetic transmit aperture (CSTA) and for comparison of the standard STA schemes. For both methods identical basic parameters – equal sequences of transmit and receive transducers were applied. The distinctive feature of CSTA is gathering (summing up) echoes of subsequent transmissions in one acquisition matrix sufficient for image reconstruction. In traditionally applied STA methods a separate acquisition matrix for each transmission is created. Therefore there are a dozen to several dozen more matrices and the time of image reconstruction is at least several times longer than in CSTA. The presented experimental results obtained using wire and tissue mimicking phantoms have shown the comparable imaging quality in both methods.
Źródło:
Hydroacoustics; 2012, 15; 195-206
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Evaluation of trabecular bone properties using ultrasonic scanne
Autorzy:
Cieślik, L.
Litniewski, J.
Lewandowski, M.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/331888.pdf
Data publikacji:
2010
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Signals scattered in trabecular bone contain information about properties of the bone structure. Evaluation of this properties may be essential for osteoporosis diagnosis and treatment monitoring because the standard densitometry does not provide complete information about the bone strength. It was previously demonstrated that using numerical model of backscattering in trabecular bone it is possible to estimate some microstructural characteristics of bone. Model predicts departures from the Rayleigh statistics of the scattered signal envelope depended on the scatterer physical parameters and its shape uniformity. This study concerns examination of trabecular bone (calcaneus) in vivo. Ultrasonic bone scanner operating at frequency of 1,5 MHz was used to collect backscattered signals. Data were processed in order to obtain the statistical properties of the signal envelope and to compare them with histograms resulting from modeling. This study is an approach towards developing a tool for the investigation of scattering in trabecular bone that can potentially provide clinically useful information about bone strength and condition.
Źródło:
Hydroacoustics; 2010, 13; 39-52
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The influence of the transducer bandwidth and double pulse transmission on the encoded imaging ultrasound
Autorzy:
Trots, I.
Nowicki, A.
Lewandowski, M.
Secomski, W.
Litniewski, J.
Powiązania:
https://bibliotekanauki.pl/articles/331651.pdf
Data publikacji:
2008
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
encoded imaging ultrasound
ultrasound imaging transducer
CGS
Opis:
An influence effect of fractional bandwidth of ultrasound imaging transducer on the gain of compressed echo signal being the complementary Golay sequences (CGS) with different spectral widths is studied in this paper. Also, a new composing transmission method of CGS is discussed together with compression technique applied in order to increase the signal-to-noise ratio (SNR) and penetration. The CGS with two different bit lengths, one-cycle and two-cycles are investigated. Two transducers with fractional bandwidth of 25% and 80% at centre frequency 6 MHz are used. The experimental results are presented, clearly proofing that increasing of the code length leads to compressed echo amplitude enhancement. The smaller the bandwidth is the larger is this effect; the pulse-echo sensitivity of the echo amplitude increases by 1.88 for 25% fractional bandwidth and 1.47 for 80% while preserving time resolution. The presented results of double transmission of short codes show the penetration and SNR improvement while maintaining dead zone.
Źródło:
Hydroacoustics; 2008, 11; 419-430
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Statistics of envelope of high frequency ultrasound signal backscattered in human dermis
Autorzy:
Piotrzkowska, H.
Litniewski, J.
Szymańska, E.
Lewandowski, M.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/331987.pdf
Data publikacji:
2010
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The scattering of ultrasonic waves depends on the size, shape, acoustical properties and concentration of scatterers in tissue. In these study K distribution of the ultrasound backscatter envelope was used to assess the structural properties of the skin tissue. The custom-designed high frequency ultrasonic scanner was applied to obtain RF B-scans of the skin in vivo at the frequency of 20 ÷ 30MHz. The results are encouraging. The K distribution models the envelope statistics very well. The parameters of the K-distribution, namely, the effective number of scatterers may be useful for the skin characterization.
Źródło:
Hydroacoustics; 2010, 13; 205-214
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Annular Array Transducer and Matched Amplifier for Therapeutic Ultrasound
Autorzy:
Secomski, W.
Nowicki, A.
Wójcik, J.
Lewandowski, M.
Walczak, M.
Tymkiewicz, R.
Powiązania:
https://bibliotekanauki.pl/articles/177840.pdf
Data publikacji:
2010
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
ultrasonic therapy
annular array transducer
ultrasonic field
Opis:
The use of therapeutic ultrasound continues to grow. A focused ultrasonic wave can increase the tissue temperature locally for the non-invasive cancer treatment or other medical applications. The authors have designed a seven-element annular array transducer operating at 2.4 MHz. Each element was excited by sine burst supplied by a linear amplifier and FPGA control circuits. The acoustic field, generated by a transducer was initially numerically simulated in a computer and next compared to water tank hydrophone measurements performed at 20, 40 and 60 mm focal depth. The results showed good agreement of the measurements with theory and the possibility to focus the ultrasound in the preselected area. The total acoustic power radiated by the annular array was equal to 2.4 W.
Źródło:
Archives of Acoustics; 2010, 35, 4; 653-660
0137-5075
Pojawia się w:
Archives of Acoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Thick Film Transducers for High Frequency Coded Ultrasonography
Autorzy:
Nowicki, A.
Lewandowski, M.
Wójcik, J.
Tymkiewicz, R.
Lou-Moller, R.
Wolny, W.
Zawada, T.
Powiązania:
https://bibliotekanauki.pl/articles/176939.pdf
Data publikacji:
2011
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
transducers
thick film
high frequency ultrasound
pulse compression
Golay codes
Opis:
Recently a new technology of piezoelectric transducers based on PZT thick film has been developed as a response to a call for devices working at higher frequencies suitable for production in large numbers at low cost. Eight PZT thick film based focused transducers with resonant frequency close to 40 MHz were fabricated and experimentally investigated. The PZT thick films were deposited on acoustically engineered ceramic substrates by pad printing. Considering high frequency and nonlinear propagation it has been decided to evaluate the axial pressure field emitted (and reflected by thick metal plate) by each of concave transducer differing in radius of curvature – 11 mm, 12 mm, 15 mm, 16 mm. All transducers were activated using AVTEC AVG-3A-PS transmitter and Ritec diplexer connected directly to Agilent 54641D oscilloscope. As anticipated, in all cases the focal distance was up to 10% closer to the transducer face than the one related to the curvature radius. Axial pressure distributions were also compared to the calculated ones (with the experimentally determined boundary conditions) using the angular spectrum method including nonlinear propagation in water. The computed results are in a very good agreement with the experimental ones. The trans- ducers were excited with Golay coded sequences at 35–40 MHz. Introducing the coded excitation allowed replacing the short-burst transmission at 20 MHz with the same peak amplitude pressure, but with almost double center frequency, resulting in considerably better axial resolution. The thick films exhibited at least 30% bandwidth broadening comparing to the standard PZ 27 transducer, resulting in an increase in matching filtering output by a factor of 1.4–1.5 and finally resulting in a SNR gain of the same order.
Źródło:
Archives of Acoustics; 2011, 36, 4; 945-954
0137-5075
Pojawia się w:
Archives of Acoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-6 z 6

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