Autor: Kujawska, T. - Prolib Integro

Skocz do pozycji: 1.

Tytuł:: Determination of the B/A of biological media by measuring and modeling nonlinear distortion of pulsed acousticwave in two-layermedia
Autorzy:: Kujawska, T.
Tematy:: acoustic wave
B/A
biological media; Pokaż więcej
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/331553.pdf Link otwiera się w nowym oknie
Opis:: The acoustic nonlinearity parameter, B/A, is a fundamental material constant characterizing nonlinear properties of biological media. Knowledge of the B/A of biological fluids or soft tissues through which pulsed acoustic waves generated from clinically relevant probes are propagating is necessary whenever high intensity pressure fields are produced. The numerical model recently developed in our lab, capable of predicting the pulsed sound fields generated from axisymmetric sources in nonlinear attenuating media, was a powerful instrument for investigating nonlinear acoustic fields produced from circular plane or focused sources in attenuating media in dependence on boundary condition parameters. Quantitative analysis of the obtained results enabled developing the alternative method for determination of the B/A parameter of biological media. First, the method involves measuring in the near field of a piezoelectric transducer the nonlinear waveform distortion of the pulsed acoustic wave propagating through the two-layer system of media: water-tested material. Then, the method involves numerical modeling, in frequency domain and under experimental boundary conditions, the nonlinear waveform distortion of the propagating wave by using the Time-Averaged Wave Envelope (TAWE) approach [1]. The obtained numerical simulation results were fitted to the experimental data by adjusting the B/A parameter of the tested material. The determined values of the B/A for standard media considered (corn oil, glycerol, pig blood, homogenized pig liver), whose density, sound velocity and attenuation law have been preliminary determined experimentally, are in a good agreement with those published. The proposed method ensure the decimal degree of accuracy, is relatively simple to use and requires small volume of tested materials that is important because of difficulty of their availability.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Pulsed Focused Nonlinear Acoustic Fields from Clinically Relevant Therapeutic Sources in Layered Media: Experimental Data and Numerical Prediction Results
Autorzy:: Kujawska, T.
Tematy:: therapeutic ultrasound
circular focused transducers
pulsed nonlinear acoustic pressure beams
layered media
numerical modeling and experiments; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/176699.pdf Link otwiera się w nowym oknie
Opis:: In many therapeutic applications of a pulsed focused ultrasound with various intensities the finite- amplitude acoustic waves propagate in water before penetrating into tissues and their local heating. Water is used as the matching, cooling and harmonics generating medium. In order to design ultrasonic probes for various therapeutic applications based on the local tissue heating induced in selected organs as well as to plan ultrasonic regimes of treatment a knowledge of pressure variations in pulsed focused nonlinear acoustic beams produced in layered media is necessary. The main objective of this work was to verify experimentally the applicability of the recently developed numerical model based on the Time- Averaged Wave Envelope (TAWE) approach (Wójcik et al., 2006) as an effective research tool for predicting the pulsed focused nonlinear fields produced in two-layer media comprising of water and tested materials (with attenuation arbitrarily dependent on frequency) by clinically relevant axially-symmetric therapeutic sources. First, the model was verified in water as a reference medium with known linear and nonlinear acoustic properties. The measurements in water were carried out at a 25.C temperature using a 2.25 MHz circular focused (f/3.0) transducer with an effective diameter of 29 mm. The measurement results obtained for 8-cycle tone bursts with three different initial pressure amplitudes varied between 37 kPa and 113 kPa were compared with the numerical predictions obtained for the source boundary condition parameters determined experimentally. The comparison of the experimental results with those simulated numerically has shown that the model based on the TAWE approach predicts well both the spatial-peak and spatial-spectral pressure variations in the pulsed focused nonlinear beams produced by the transducer used in water for all excitation levels complying with the condition corresponding to weak or moderate source-pressure levels. Quantitative analysis of the simulated nonlinear beams from circular transducers with ka ť 1 allowed to show that the axial distance at which sudden accretion of the 2nd or higher harmonics amplitude appears is specific for this transducer regardless of the excitation level providing weak to moderate nonlinear fields. For the transducer used, the axial distance at which the 2nd harmonics amplitude suddenly begins to grow was found to be equal to 60 mm. Then, the model was verified experimentally for two-layer parallel media comprising of a 60-mm water layer and a 60-mm layer of 1.3-butanediol (99%, Sigma-Aldrich Chemie GmbH, Steinheim, Germany). This medium was selected because of its tissue-mimicking acoustic properties and known nonlinearity parameter B/A. The measurements of both, the peak- and harmonic-pressure variations in the pulsed nonlinear acoustic beams produced in two-layer media (water/1.3-butanediol) were performed for the same source boundary conditions as in water. The measurement results were compared with those simulated numerically. The good agreement between the measured data and numerical calculations has shown that the model based on the TAWE approach is well suited to predict both the peak and harmonic pressure variations in the pulsed focused nonlinear sound beams produced in layered media by clinically relevant therapeutic sources. Finally, the pulsed focused nonlinear fields from the transducer used in two-layer media: water/castor oil, water/silicone oil (Dow Corning Ltd., Coventry, UK), water/human brain and water/pig liver were predicted for various values of the nonlinearity parameter of tested media.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Harmonic ultrasound beams forming by means of radiating source parameters
Autorzy:: Kujawska, T.
Wójcik, J.
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/332171.pdf Link otwiera się w nowym oknie
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.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Nonlinear effects computed in Gaussian beams propagating in liquids
Autorzy:: Wójcik, W.
Kujawska, T.
Filipczyński, L.
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/332053.pdf Link otwiera się w nowym oknie
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.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: Automated bimodal ultrasound device for preclinical testing of HIFU technique in treatment of solid tumors implanted into small animals
Autorzy:: Kujawska, T.
Dera, W.
Dziekoński, C.
Tematy:: High Intensity Focused Ultrasound beam
focal volume
tissue damage; Pokaż więcej
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/332489.pdf Link otwiera się w nowym oknie
Opis:: In Poland cancer is the second cause of death overall, and the first before 65. Demand for new anticancer therapies is increasing every year. The main objective of studies on medical and technical aspects of new anticancer methods is to reduce unwanted side effects and costs associated with conventional methods of treatment. Percutaneous (noninvasive) HIFU (High Intensity Focused Ultrasound) technique gives the chance to radically reduce both of these factors. The main goal of this work is automation of HIFU technology for producing thermal damage to the entire volume of a solid breast tumor implanted into a rat mammary gland using the proposed bi-modal ultrasound equipment, enabling the ultrasonic heating of a small volume within the tumor under the ultrasonic imaging control, as well as 3D scanning of the heating beam focus throughout the entire tumor volume. Design of the proposed equipment includes the heating probe of low frequency (about 1MHz), allowing penetration of pulsed focused waves into tissues, and the linear phased array probe of high frequency (from 4 MHz to 10 MHz), allowing visualization of the locally heated area inside the tumor in real time. Automatic 3D scanning of the heating beam focus provides the thermal damage to its entire volume.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: Numerical modeling of ultrasound-induced temperature fields in multilayer nonlinear attenuating media
Autorzy:: Kujawska, T.
Wójcik, J.
Nowicki, A.
Tematy:: numerical modeling
ultrasound
attenuating media; Pokaż więcej
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/332786.pdf Link otwiera się w nowym oknie
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.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Temperature fields induced in rat liver in vitro by pulsed low intensity focused ultrasound
Autorzy:: Kujawska, T.
Wójcik, J.
Nowicki, A.
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/331934.pdf Link otwiera się w nowym oknie
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.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Nonlinear and linear pressure determination in a two-layer structure: solid crystal - water at GHz frequencies
Autorzy:: Filipczyński, L.
Wójcik, J.
Kujawska, T.
Tematy:: pressure determination
solid crystal
water
GHz frequencies; Pokaż więcej
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/332574.pdf Link otwiera się w nowym oknie
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.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: Nonlinear ultrasound propagation in water from square focused transducer
Autorzy:: Kujawska, T.
Wójcik, J.
Nowicki, A.
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/332715.pdf Link otwiera się w nowym oknie
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.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 10.

Tytuł:: Foundation of the new method of numerical calculations of the nonlinear acoustics fields
Autorzy:: Wójcik, J.
Filipczyński, L.
Kujawska, T.
Nowicki, A.
Wydawca:: Polskie Towarzystwo Akustyczne
Powiązania:: https://bibliotekanauki.pl/articles/332125.pdf Link otwiera się w nowym oknie
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.
Dostawca treści:: Biblioteka Nauki

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