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Wyświetlanie 1-15 z 27
Tytuł:
Dynamic ultrasonic model of left ventricle
Autorzy:
Trawiński, Z.
Wójcik, J.
Nowicki, A.
Olszewski, R.
Powiązania:
https://bibliotekanauki.pl/articles/332195.pdf
Data publikacji:
2013
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Two different tissue phantoms of the left ventricle to imitate a beating left ventricle were developed: first was prepared using a sponge material and second phantom was constructed using a polyvinyl alcohol material modeled into a homogeneous hollow cylinder: approximately 10 cm and 12 cm in length for the first and second phantom, respectively. Both phantoms were 5 cm in diameter, with a wall thickness of 1.0 cm. Additionally, a small part of the wall of the second phantom was processed to simulate the stiffness of myocardial infarction. The phantoms were connected at the end to an adjustable external pump. The pulse volume inside the cylinder was set between 12 to 50 ml at rates of 40, 60, 100, 120 beats/minute. The phantoms were immersed in water for ultrasound scanning with two different insonation angles (90 and 65 degrees). Strain and strain rate were measured with different combinations of angles and pulse rates. The main aim of this work was to develop the new method for validation of the human infarct wall strain calculation procedures using the speckles tracking.
Źródło:
Hydroacoustics; 2013, 16; 231-236
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Harmonic ultrasound beams forming by means of radiating source parameters
Autorzy:
Kujawska, T.
Wójcik, J.
Powiązania:
https://bibliotekanauki.pl/articles/332171.pdf
Data publikacji:
2004
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
In the paper the investigation results of the influence of such parameters as shape and size of the radiating source, as well as waveform, frequency and amplitude of the propagating pulse on the non-linear ultrasonic beam forming are presented. The analysis was carried out on the basis of numerical simulations of the amplitude and harmonic field distributions, in space and time, of two-dimensional beams propagating in water. The applied software (numerical solver), describing the nonlinear propagation of the ultrasonographic pulse wave radiated by the axially symmetrical source in the layered lossy medium for given boundary conditions, was used as the tool to predict the behavior of the ultrasound beam. The algorithm of the above numerical solver, proposed by the second author, is based on the frequency-domain numerical solution of the non-linear wave equation for finite amplitude sound beams. It takes into account the influence of the effects of diffraction, non-linearity and thermoviscous absorption on the propagation of the finite amplitude acoustic beam in attenuating media.
Źródło:
Hydroacoustics; 2004, 7; 135-142
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Nonlinear effects computed in Gaussian beams propagating in liquids
Autorzy:
Wójcik, W.
Kujawska, T.
Filipczyński, L.
Powiązania:
https://bibliotekanauki.pl/articles/332053.pdf
Data publikacji:
2001
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The existing theory of focused Gaussian nonlinear beams is based on the parabolic approximation which is not valid near to the sound source, and is restricted to weakly concave transducers. The authors have solved the exact problem of nonlinear propagation of focused Gaussian beams in lossy media without the above limitations. For this purpose a numerical model of the first author was used.
Źródło:
Hydroacoustics; 2001, 4; 257-260
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Multitone nonlinear coding
Autorzy:
Nowicki, A.
Wójcik, J.
Secomski, W.
Powiązania:
https://bibliotekanauki.pl/articles/331604.pdf
Data publikacji:
2008
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
MNC method
virtual fields
acoustic source
Opis:
A new method that utilizes nonlinear properties of tissue (or another media) to improve ultrasound image resolution is presented. In our novel method the acoustic source is activated with two tones burst (2.2 and 4.4 MHz) with specially designed polarization of the individual tone burst. This new approach is called multi tone nonlinear coding MNC because the choice of polarization of the both tones (and their amplitudes) allowing optimization of the receiving properties depends on the nonlinear properties of tissue. The calculations were done for two tones bursts propagating in the tissue-like lossy medium with absorption of 7 Np/mźMHz. The concept of the Virtual Fields was introduced to explain abilities and properties of pulse inversion and MNC method and to compare both. Comparison of the spatial field distribution obtained using MNC and conventional harmonic imaging approach, in which the first harmonic is used to reconstruct the image are presented.
Źródło:
Hydroacoustics; 2008, 11; 289-298
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Nonlinear ultrasound propagation in water from square focused transducer
Autorzy:
Kujawska, T.
Wójcik, J.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/332715.pdf
Data publikacji:
2005
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The nonlinear pulsed acoustic pressure field from a focused square aperture is considered. Experimental measurements in water of a 4D sound field radiated from a 2.8 MHz focused square transducer of a 20 mm side and a 80 mm focal distance for excitation level producing an average acoustic pressure P0 = 0.14 MPa at its surface are presented. The obtained results are compared with the numerical calculation results for the same boundary conditions. The novel, free from paraxial approximation and computationally efficient numerical algorithm was used to simulate the 4D nonlinear pulsed pressure field from the nonaxisymmetric acoustic source. Our theoretical model was based on the Time-Averaged Pressure Envelope (TAPE) method recently developed that enable to represent the propagated pulsed disturbance as a superposition of sinusoidal wavelets with carrier frequencies being the harmonics of the initial tone burst and with envelopes determined by the TAPE method. The novel approach to the solution of the nonlinear wave equation enabled to simulate full 4D nonlinear field for given boundary conditions in a dozen or so minutes utilizing the computational power of the standard PC.
Źródło:
Hydroacoustics; 2005, 8; 89-98
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Applying crystallography in analysis of trabecular bone backscatter
Autorzy:
Wojcik, J.
Litniewski, J.
Nowicki, A.
Gambin, B.
Powiązania:
https://bibliotekanauki.pl/articles/332506.pdf
Data publikacji:
2011
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Some important details of the Backscatter Effective Cross-Sections obtained for random scattering structures (like trabecular bone) are explain by comparison with the results obtained by means of the simplified theoretical model. The simplified model was (establish) and justified on the basis of the structural analysis of the results obtained for exact model of the field scattering on complex structures. The simplified model is commonly used in description of the scattering on the regular structures like crystal. Comparison with experimental results for the trabecular bone is also presented. The results allowed to conclude that crystallographic methods could be potentially useful for extracting characteristic features of trabecular bone.
Źródło:
Hydroacoustics; 2011, 14; 255-266
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ultrasound imaging of stiffness with two frequency pulses
Autorzy:
Nowicki, A.
Byra, M.
Litniewski, J.
Wójcik, J.
Powiązania:
https://bibliotekanauki.pl/articles/332602.pdf
Data publikacji:
2014
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Nowadays there are new modalities in ultrasound imaging allowing better characterization of tissue regions with different stiffness. We are proposing a novel approach based on compression and rarefaction of tissue simultaneously with imaging. The propagating wave is a combination of two pulses. A low frequency pulse is expected to change the local scattering properties of the tissue due to compression/rarefaction while a high frequency pulse is used for imaging. Two transmissions are performed for each scanning line. First, with the imaging pulse that propagates on maximum compression caused by a low frequency wave. Next, the low frequency wave is inverted and the imaging pulse propagates over the maximum rarefaction. After the processing of the subtracted echoes from subsequent transmissions including wavelet transform and band-pass filtering, differential images were reconstructed. The low frequency wave has a visible impact on the scattering properties of the tissue which can be observed on a differential image.
Źródło:
Hydroacoustics; 2014, 17; 151-160
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ilościowa ocena nieliniowej propagacji w wodzie i w tkance
Autorzy:
Filipczyński, L.
Kujawska, T.
Tymkiewicz, R.
Wójcik, J.
Powiązania:
https://bibliotekanauki.pl/articles/331916.pdf
Data publikacji:
2000
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Nonlinear propagation effects were investigated numerically and experimentally u wate r and In blood from the point of view of ultrasonic diagnostic applications in cardlology. Pressure distributions of short and long pulses with the frequency of 3 and 3.5 MHz, radiated by a typical cardiological probe, were found along the ultrasonic beam axis. The numerial results were obtained by means of the numerical code Wf developed previously. The experimental pressure distributions were measured by memu of a membrane PYDF hydrophone. The obtained numerical and experimental results show ing the distributions of the 2-nd and I -st harmonics have shown good agreement allowing us to determine some diagnostic conclusions.
Źródło:
Hydroacoustics; 2000, 3; 53-56
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical solver of acoustic field in simulation of artery wall thickness examinations
Autorzy:
Powałowski, T.
Wójcik, J.
Trawiński, Z.
Powiązania:
https://bibliotekanauki.pl/articles/332572.pdf
Data publikacji:
2007
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The aim of the study was the elaboration of a mathematical model to describe the process of acoustic wave propagation, generated by an ultrasonic probe in a inhomogenous loosing medium. Numerical calculations make it possible to define waveforms for electric signals that are generated when ultrasonic waves, being reflected and backscattered by an artery model, are then received by the ultrasonic probe. It is the signal that pretty well corresponds with the actual RF signal that is obtained during measurements at the output of the ultrasonic apparatus. The developed solver of acoustic field was used for simulation of the artery wall thickness examination. The theoretical model of the artery for the creating the simulated ultrasonic reflected echoes was used. The internal radius of the artery model was 3 mm for the diastolic pressure and 3.3 mm for the systolic pressure. The intima-media thickness (IMT) of the artery wall was changed from 0.48 mm to 0,44 mm respectively. The solver based on zero-crossing method was used for detecting changes of the IMT.
Źródło:
Hydroacoustics; 2007, 10; 163-168
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
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:
A spectral-based method for tissue characterization
Autorzy:
Wójcik, J.
Byra, M.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/331796.pdf
Data publikacji:
2016
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
quantitative ultrasound
signal analysis
wave scattering
Opis:
Quantitative ultrasound methods are widely investigated as a promising tool for tissue characterization. In this paper, a novel quantitative method is developed which can be used to assess scattering properties of tissues. The proposed method is based on analysis of oscillations of the backscattered echo power spectrum. It is shown that these oscillations of the power spectrum are connected with the distances between scatterers within the medium. Two techniques are proposed to assess the scatterer’s distribution. First, we show that the inverse Fourier transform of the backscattered echo power spectrum corresponds to a histogram of the distances between scatterers. Second, the Hilbert-Huang transform is used to directly extract the power spectrum oscillations. Both methods are examined by means of a numerical experiment. A cellular gas model of a biological medium is considered. Results are presented and discussed. Both methods can be used to evaluate the scatterer’s distribution by means of the power spectrum oscillations.
Źródło:
Hydroacoustics; 2016, 19; 369-375
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Foundation of the new method of numerical calculations of the nonlinear acoustics fields
Autorzy:
Wojcik, J.
Filipczyński, L.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/332217.pdf
Data publikacji:
2013
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
We explain, motivation behind this work and briefly describe foundation of new method which we have developed for efficient solution in PC environment of the nonlinear propagation equation with the boundary conditions applied for both circular and not circular transducers (like array). Comparison between new and old method will be presented for strongly nonlinear disturbance. At the end we will demonstrate the results of the numerical calculations of the nonlinear field propagating from the array.
Źródło:
Hydroacoustics; 2013, 16; 253-262
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Acoustic streaming generated by ultrasonic transducers, measurements by means of 32 MHz Doppler
Autorzy:
Nowicki, A.
Secomski, W.
Wójcik, J.
Powiązania:
https://bibliotekanauki.pl/articles/332760.pdf
Data publikacji:
1997
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
An approximate solution for the streaming velocity generated by flat and weakly focused transducers was derived by directly solving the Dirichlet boundary conditions for the Poisson equation. The theoretical calculations were verified using a purpose-designed 32 MHz pulsed Doppler unit. The applied average acoustic power was changed from l µW to 6 mW. The experiments were done on 4 mm diameter flat and focused transducers. The streaming velocity was measured along the ultrasonic beam from 0 to 20 mm. Streaming was induced in a solution of water and com starch. The experimental results showed that for a given acoustic power the streaming velocity was independent of the starch density in water changed from 0.3 grams to 40 grams of starch in 1 litre of distilled water. For applied acoustic powers, the streaming velocity changed Iinearly from 0.2 to 40 mm/s. Both, the theoretical solutions for pIane and focused waves, and the experimental results were in good agreement.
Źródło:
Hydroacoustics; 1997, 1; 337-342
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Multiple scattering contribution to trabecular bone backscatter
Autorzy:
Wójcik, J.
Litniewski, J.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/332838.pdf
Data publikacji:
2009
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
bone backscatter
integral equations
spectral distribution
Opis:
Integral equations that describe scattering on the structure with step rise parameters, have been numerically solved on example of the trabecular bone model. The model consists of several hundred elements with randomly selected parameters. The spectral distribution of scatter coefficients in subsequent orders of scattering has been presented.
Źródło:
Hydroacoustics; 2009, 12; 227-236
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Temperature fields induced in rat liver in vitro by pulsed low intensity focused ultrasound
Autorzy:
Kujawska, T.
Wójcik, J.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/331934.pdf
Data publikacji:
2010
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Beneficial biological effects in soft tissues can be induced by focused ultrasound of low intensity (LIFU). For example, increasing of cells immunity to stress can be accomplished through the enhanced heat shock proteins (Hsp) expression induced by the low intensity focused ultrasound. The possibility to control the Hsp expression enhancement in soft tissues in vivo can be the potential new therapeutic approach to neurodegenerative diseases that utilizes the known feature of cells to increase their immunity to stresses through the Hsp expression enhancement. The controlling of the Hsp expression enhancement by adjusting the level of exposure to ultrasound energy would allow evaluating of ultrasound-mediated treatment efficiency. Our objective was to develop the numerical model capable of predicting in space and time temperature fields induced in multilayer nonlinear attenuating media by a circular focused transducer generating pulsed acoustic waves and to compare the results calculated for two-layer configuration of media: water - fresh rat liver with the experimental data. The measurements of temperature variations versus time at 5 points on the acoustic beam axis within the tissue sample were performed using 0.2-mm diameter thermocouples. Temperature fields were induced by the transducer with 15-mm diameter, 25-mm focal length and 2-MHz centre frequency generating tone bursts with the intensity ISPTA varied between 0.45 W/cm2 and 1.7 W/cm2 and duration varied between 20 and 500 cycles at the same 20-% duty cycle and 20-min exposure time. Quantitative analysis of the obtained results allowed to show that, for example, for the acoustic beam with intensity ISPTA = 1.13 W/cm2 exposure time to ultrasound should not be longer than 10 min to avoid cells necrosis following the 43-oC temperature threshold exceeding.
Źródło:
Hydroacoustics; 2010, 13; 153-162
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 27

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