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Wyświetlanie 1-15 z 26
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:
Theoretical results and numerical study on the nonlinear reflection and transmission of plane sound waves
Autorzy:
Wojcik, J.
Gambin, B.
Litniewski, J.
Powiązania:
https://bibliotekanauki.pl/articles/332766.pdf
Data publikacji:
2015
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
theoretical and numerical model
continuity conditions
non-linear waves
lossy media
Opis:
The comparison between theoretical and numerical solutions of the reflection/transmission problem for the acoustic plane wave normally incident on the discontinuity surface between two nonlinear lossy media was presented. Numerical calculations made under the assumption that the two media have the same impedance, allow to single out the effect of nonlinearities in the description of the reflection and transmission phenomena, so they agreed with theoretical predictions. It was shown that theoretically obtained and numerically calculated results mutually confirmed themselves.
Źródło:
Hydroacoustics; 2015, 18; 181-192
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:
Numerical modeling of ultrasound-induced temperature fields in multilayer nonlinear attenuating media
Autorzy:
Kujawska, T.
Wójcik, J.
Nowicki, A.
Powiązania:
https://bibliotekanauki.pl/articles/332786.pdf
Data publikacji:
2009
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
numerical modeling
ultrasound
attenuating media
Opis:
Ultrasound is a safe, convenient and inexpensive modality which may be useful for soft tissues treatment. A range of beneficial biological effects induced by ultrasound depends on the exposure levels used during treatment. At high intensities instantaneous tissue necrosis is desired, whereas at lower intensities remedial reversible cellular effects may be produced. For example, increasing of cells immunity against stress can be obtained through the heat shock proteins (Hsp) expression enhancement. The possibility of the Hsp expression enhancement in soft tissues in vivo by means of controlled exposure to ultrasound would allow to evaluate the treatment efficiency. Ultrasonic regimes can be controlled by adjusting the ultrasound intensity, frequency, pulse duration, duty cycle and exposure time. The goal of this work was to develop the numerical model capable of predicting in space and time the temperature fields induced by circular focused transducer generating tone bursts in multilayer nonlinear attenuating media, which is intended for the Hsp expression enhancement therapeutic application. The acoustic pulsed pressure field generated from the transducer was calculated using our original 3D numerical solver [1]. For prediction of the temperature distributions in multilayer biological media the Pennes bio-heat transfer equation was numerically solved. The 3D temperature fields induced in a rat liver in vitro by a 2 MHz transducer with 15 mm diameter and 25 mm focal length during ultrasonic Hsp expression enhancement treatment using various acoustic beam intensities and exposure time was predicted.
Źródło:
Hydroacoustics; 2009, 12; 91-97
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:
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:
Differentiation of random structure properties using wavelet analysis of backscattered ultrasound
Autorzy:
Gambin, B.
Wojcik, J.
Doubrovina, O.
Powiązania:
https://bibliotekanauki.pl/articles/331612.pdf
Data publikacji:
2016
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
spectrogram
scalogram
wavelets
random scattering structure
Opis:
The aim of this work was to find the differences between random media by analyzing the properties of the ultrasound signals backscattered from the inhomogeneities. A numerical model is used to generate two types of random media. The first has the randomness in scatterers’ positions and the second has the randomness in the size and acoustical properties of scatterers. The numerical model of wave scattering has been used to simulate the RF (radio frequency) signals caused by the incident pulse traveling as a plane wave. The markers of randomness type differences between the scattering media were obtained with the help of the spectral and wavelet analysis. The effect of differences in randomness type is more spectacular when the wavelet analysis is performed.
Źródło:
Hydroacoustics; 2016, 19; 121-128
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Comparison of experimental results and numerical calculations of ultrasonic waves scattering on a model of the artery
Autorzy:
Wójcik, J.
Trawiński, Z.
Powałowski, T.
Powiązania:
https://bibliotekanauki.pl/articles/331649.pdf
Data publikacji:
2008
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
ultrasonic waves
artery model
transmitted ultrasound
Opis:
The aim of this paper is to compare the results of the mathematical modeling and experimental results of the ultrasonic waves scattering in the inhomogeneous dissipative medium. The research was carried out for an artery model (a pipe made of a latex), with internal diameter of 3, 5 and 8 mm and wall thickness of 0.75, 1.25 and 2 mm. The numerical solver was created for calculation of the fields of ultrasonic beams and scattered fields under different boundary conditions, different angles and transversal displacement of ultrasonic beams with respect to the position of the arterial wall. The investigations employed the VED ultrasonic apparatus. The frequency of the transmitted ultrasound was 6.75 MHz. The good agreement between the numerical calculation and experimental results was obtained. The numerical solver is used for verified proposed methods for determining of the IMT in the artery walls.
Źródło:
Hydroacoustics; 2008, 11; 449-458
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:
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
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:
Nonlinear and linear pressure determination in a two-layer structure: solid crystal - water at GHz frequencies
Autorzy:
Filipczyński, L.
Wójcik, J.
Kujawska, T.
Powiązania:
https://bibliotekanauki.pl/articles/332574.pdf
Data publikacji:
2003
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
pressure determination
solid crystal
water
GHz frequencies
Opis:
Determination of acoustic pressures at the frequency of 1 GHz by means of PVDF hydrophones is not possible due to their limited frequency response. Moreover, the size of their active electrodes is by about 3 orders of magnitude greater than the resolution in the acoustic microscopes at such a high frequency. Therefore the authors solved this problem at first in a microscope with the working frequency of 34 MHz using both the numerical and experimental methods. A numerical procedure of nonlinear propagation and transducer power measurements were applied giving in effect the same quantitative results. Therefore the identical numerical procedure was used for the l GHz microscope working in the reflection mode. Many pressure field quantities of the microscope were shown, e.g. the pressure values, distributions of the first, second, third and fourth pressure harmonics in and outside of the focus, pulse distortions and their spectra, the resolutions achieved etc. The obtained information on nonlinear propagation effects in microscopy was previously lacking.
Źródło:
Hydroacoustics; 2003, 6; 143-150
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:
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:
Relationship between thermal and ultrasound fields in breast tissue in vivo
Autorzy:
Gambin, B.
Kruglenko, E.
Wójcik, J.
Powiązania:
https://bibliotekanauki.pl/articles/332806.pdf
Data publikacji:
2015
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
backscattered ultrasonic signal
non-uniform temperature field
Opis:
The study shows the direct relationship between the temperature field and the parallel changes that are taking place in backscattered ultrasonic signals from the breast tissue in vivo when heated to the temperature of approximately 42 deg. C. The non-uniform temperature field inside the heating tissue was determined by the numerical model using FEM. It is shown that the spatial distribution of intensities of the backscattered signals coincides with the temperature distribution field predicted by the numerical model in some areas. The result indicates the possibility of the indirect measurement of the temperature rise in the breast tissue in vivo by measuring the intensity variations of the ultrasound echo.
Źródło:
Hydroacoustics; 2015, 18; 53-58
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 26

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