1. |
Miklewska A., Tymkiewicz R., Kruglenko E., Krajewski M., Gambin B., Comparison of the influence of superparamagnetic nanoparticles concentration and coverage on the alternating magnetic field thermal effect,
Journal of Magnetism and Magnetic Materials, ISSN: 0304-8853, DOI: 10.1016/j.jmmm.2021.168918, 10.1016/j.jmmm.2022.169422, Vol.550, pp.168918-1-6, 2022Streszczenie: Magnetic nanoparticles (MNP)s of Fe3O4 were synthesized in the co-precipitation reaction of iron chlorides dissolved in water and ammonia water. To produce polyethylene glycol (PEG) coatings of the NMPs, we added PEG to the ammonia water during the fabrication process. Magnetic fluids, ferrofluids, for research were prepared as oleic acid suspension of bare and PEG-coated nanoparticles at four concentrations. The results of the conducted calorimetric experiments confirmed that the efficiency of heating ferrofluids strongly depends on the concentration of nanoparticles in fluids. The results also indicate that the ferrofluids containing PEG-coated NPs heat up more than ferrofluids with bare nanoparticles. They are characterized by a higher specific absorption rate (SAR) value calculated from the initial slope of temperature versus time curve during heating. Słowa kluczowe: nanoparticle fluid hyperthermia, magnetite nanoparticles, PEG-coated nanoparticles, hyperthermia Afiliacje autorów:
Miklewska A. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Kruglenko E. | - | IPPT PAN | Krajewski M. | - | IPPT PAN | Gambin B. | - | IPPT PAN |
| | 100p. |
2. |
Mieldzioć P.^{♦}, Tymkiewicz R., Sołek J.^{♦}, Secomski W., Litniewski J., Fita P.^{♦}, Reaction kinetics of sonochemical oxidation of potassium hexacyanoferrate(II) in aqueous solutions,
Ultrasonics Sonochemistry, ISSN: 1350-4177, DOI: 10.1016/j.ultsonch.2019.104912, Vol.63, pp.104912-1-8, 2020Streszczenie: We studied sonochemical reactions resulting from ultrasonic treatment of potassium hexacyanoferrate(II) in aqueous solutions using a custom-built apparatus working at 536 kHz. We concluded that primary reactions are completely dominated by oxidation of Fe(II) to Fe(III) and did not find any evidences for degradation of cyanide. At the highest concentration used in the present study (0.1 M) we detected formation of pentacyanoaquaferrate(II) complex, which is most probably formed in reactions between hexacyanoferrate(III) anions and hydrogen atoms or hydrated electrons formed in sonochemical processes. We also determined that hydroxyl radicals formation rate in our system, (8.7 ± 1.5)∙10^-8 M∙s^-1, is relatively high compared to other reported experiments. We attribute this to focusing of the ultrasonic wave in the sample vessel. Finally, we suggest that oxidation rate of hexacyanoferrate(II) anions can be a convenient benchmark of efficiency of sonochemical reactors. Słowa kluczowe: sonochemistry, sonooxidation, sonoreactor, advanced oxidation processes, waste-water treatment Afiliacje autorów:
Mieldzioć P. | - | Uniwersytet Warszawski (PL) | Tymkiewicz R. | - | IPPT PAN | Sołek J. | - | Uniwersytet Warszawski (PL) | Secomski W. | - | IPPT PAN | Litniewski J. | - | IPPT PAN | Fita P. | - | Uniwersytet Warszawski (PL) |
| | 140p. |
3. |
Zaszczyńska A., Sajkiewicz P.Ł., Gradys A., Tymkiewicz R., Urbanek O., Kołbuk D., Influence of process-material conditions on the structure and biological properties of electrospun polyvinylidene fluoride fibers,
BULLETIN OF THE POLISH ACADEMY OF SCIENCES: TECHNICAL SCIENCES, ISSN: 0239-7528, DOI: 10.24425/bpasts.2020.133368, Vol.68, No.3, pp.627-633, 2020Streszczenie: Polyvinylidene fluoride (PVDF) is one of the most important piezoelectric polymers. Piezoelectricity in PVDF appears in polar β and ɣ phases. Piezoelectric fibers obtained by means of electrospinning may be used in tissue engineering (TE) as a smart analogue of the natural extracellular matrix (ECM). We present results showing the effect of rotational speed of the collecting drum on morphology, phase content and in vitro biological properties of PVDF nonwovens. Morphology and phase composition were analyzed using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), respectively. It was shown that increasing rotational speed of the collector leads to an increase in fiber orientation, reduction in fiber diameter and considerable increase of polar phase content, both b and g. In vitro cell culture experiments, carried out with the use of ultrasounds in order to generate electrical potential via piezoelectricity, indicate a positive effect of polar phases on fibroblasts. Our preliminary results demonstrate that piezoelectric PVDF scaffolds are promising materials for tissue engineering applications, particularly for neural tissue regeneration, where the electric potential is crucial. Słowa kluczowe: scaffolds, electrospinning, polyvinylidene fluoride, tissue engineering Afiliacje autorów:
Zaszczyńska A. | - | IPPT PAN | Sajkiewicz P.Ł. | - | IPPT PAN | Gradys A. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Urbanek O. | - | IPPT PAN | Kołbuk D. | - | IPPT PAN |
| | 100p. |
4. |
Tasinkiewicz J., Trots I., Tymkiewicz R., Theoretical analysis and experimental verification of top orthogonal to bottom arrays of conducting strips on piezoelectric slab,
ARCHIVES OF ACOUSTICS, ISSN: 0137-5075, DOI: 10.24425/aoa.2020.134059, Vol.45, No.3, pp.433-444, 2020Streszczenie: The purpose of this work is to present a theoretical analysis of top orthogonal to bottom arrays of conducting electrodes of infinitesimal thickness (conducting strips) residing on the opposite surfaces of piezoelectric slab. The components of electric field are expanded into double periodic Bloch series with corresponding amplitudes represented by Legendre polynomials, in the proposed semi-analytical model of the considered two-dimensional (2D) array of strips. The boundary and Edge conditions are satisfied directly by field representation, as a result. The method results in a small system of linear equations for unknown expansion coefficients to be solved numerically. A simple numerical example is given to illustrate the method. Also a test transducer was designed and a pilot experiment was carried out to illustrate the acoustic-wave generating capabilities of the proposed arrangement of top orthogonal to bottom arrays of conducting strips. Słowa kluczowe: boundary value problem, Fourier series, Bloch series, partial differential equations, piezoelectric transducer Afiliacje autorów:
Tasinkiewicz J. | - | IPPT PAN | Trots I. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN |
| | 70p. |
5. |
Gambin B., Kruglenko E., Tymkiewicz R., Litniewski J., Ultrasound assessment of the conversion of sound energy into heat in tissue phantoms enriched with magnetic micro- and nanoparticles,
Medical Physics, ISSN: 0094-2405, DOI: 10.1002/mp.13742, Vol.46, No.10, pp.4361-4370, 2019Streszczenie: Purpose: Nowadays, the improvement of ultrasonic hyperthermia therapy is often achieved by adding hard particles to the sonicated medium in order to increase the heating efficiency. The explanation of the phenomenon of ultrasonic heating still requires testing on tissue mimicking materials (TMMs), enriched with particles of different sizes and physical properties. Our goal was to determine, by comparing their quantitative acoustic properties, which TMMs, with magnetic micro- or nanoparticles, convert more ultrasonic energy into heat or which of the particles embedded in the agar gel act as more effective thermal sonosensitizers. Methods: We manufactured a pure agar gel and an agar gel with the addition of magnetic micro- or nanoparticles in two proportions of 8 and 16 mg/ml. Ultrasound quantitative techniques, the broadband reflection substitution technique and backscattered spectrum analysis were used to characterize the samples by speed of sound (SOS), frequency-dependent attenuation, and backscattering coefficients. The integrated backscattering coefficients were also calculated. The quantitative parameters, scattering, and attenuation coefficients of ultrasound in phantoms with micro- and nanoparticles were estimated. Based on the attenuation and scattering of ultrasound in the samples, the ultrasonic energy absorption, which determines the heating efficiency, was evaluated. Additionally, the temperature increase during sonication of the phantoms by an ultrasonic beam was directly measured using thermocouples. Results: The density of the materials with nanoparticles was higher than for the materials with microparticles with the same fractions of particles. The SOS for all materials ranged from 1489 to 1499 m/s. The attenuation in the whole frequency range (3–8 MHz) was higher for the materials with nanoparticles than for the materials with microparticles. For the materials with the lower content (8 mg/ml) of particles, the attenuation coefficient was 0.2 dB/(MHz cm). For the 16 mg/ml concentration of nanoparticles and microparticles, the attenuation coefficients were 0.66 and 0.45 dB/(MHz cm), resectively. The value of backscattering coefficient in the whole frequency range was greater for the materials with microparticles than for the materials with nanoparticles. The values of the integrated backscattering coefficient were 0.05 and 0.08 1/m for the materials with nanoparticles and 0.46 and 0.82 1/m for the materials with microparticles and concentrations of 8 and 16 mg/ml, respectively. The rates of temperature increase in the first 3 s due to ultrasonic heating were higher for the materials with nanoparticles than for the materials with microparticles. Conclusions: Based on acoustical measurements, we confirmed that all materials can be used as tissue phantoms in the study of ultrasonic hyperthermia, as their properties were in the range of soft tissue properties. We found that the nanoparticle-doped materials had greater attenuation and smaller scattering of ultrasound than the materials with microparticles, so absorption in these materials is greater. Thus, the TMMs with nanoparticles convert more acoustic energy into heat and we conclude that magnetic nanoparticles are more effective thermal sonosensitizers than microparticles. This conclusion is confirmed by direct measurement of the temperature increase in the samples subjected to sonification. Słowa kluczowe: backscattering coefficient, frequency-dependent attenuation, hyperthermia TMM, magnetic particles, ultrasound absorption Afiliacje autorów:
Gambin B. | - | IPPT PAN | Kruglenko E. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Litniewski J. | - | IPPT PAN |
| | 100p. |
6. |
Nowicki A., Gambin B., Secomski W., Trawiński Z., Szubielski M.^{♦}, Tymkiewicz R., Olszewski R.^{♦}, Assessment of high frequency imaging and Doppler system for the measurements of the radial artery flow-mediated dilation,
ARCHIVES OF ACOUSTICS, ISSN: 0137-5075, DOI: 10.24425/aoa.2019.129276, Vol.44, No.4, pp.637-644, 2019Streszczenie: In the article we describe the new, high frequency, 20 MHz scanning/Doppler probe designed to measure the flow mediated dilation (FMD) and shear rate (SR) close to the radial artery wall. We compare two US scanning systems, standard vascular modality working below 12 MHz and high frequency 20 MHz system designed for FMD and SR measurements. Axial resolutions of both systems were compared by imaging of two closely spaced food plastic foils immersed in water and by measuring systolic/diastolic diameter changes in the radial artery. The sensitivities of Doppler modalities were also determined. The diagnostic potential of a high frequency system in measurements of FMD and SR was studied in vivo, in two groups of subjects, 12 healthy volunteers and 14 patients with stable coronary artery disease (CAD). Over three times better axial resolution was demonstrated for a high frequency system. Also, the sensitivity of the external single transducer 20 MHz pulse Doppler proved to be over 20 dB better (in terms of a signal-to-noise ratio) than the pulse Doppler incorporated into the linear array. Statistically significant differences in FMD and FMD/SR values for healthy volunteers and CAD patients were confirmed, p-values < 0:05. The areas under Receiver Operating Characteristic (ROC) curves for FMD and FMD/SR for the prediction CAD had the values of 0.99 and 0.97, respectively. These results justify the usefulness of the designed high-frequency scanning system to determine the FMD and SR in the radial artery as predictors of coronary arterial disease. Słowa kluczowe: low mediated dilation, shear rate, axial resolution, elevation resolution, pulsed Doppler, ultrasonic imaging Afiliacje autorów:
Nowicki A. | - | IPPT PAN | Gambin B. | - | IPPT PAN | Secomski W. | - | IPPT PAN | Trawiński Z. | - | IPPT PAN | Szubielski M. | - | Mazovia Regional Hospital in Siedlce (PL) | Tymkiewicz R. | - | IPPT PAN | Olszewski R. | - | inna afiliacja |
| | 70p. |
7. |
Litniewski J., Cieślik L., Lewandowski M., Tymkiewicz R., Zienkiewicz B., Nowicki A., Ultrasonic Scanner for In Vivo Measurement of Cancellous Bone Properties From Backscattered Data,
IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, ISSN: 0885-3010, DOI: 10.1109/TUFFC.2012.2347, Vol.59, No.7, pp.1470-1477, 2012Streszczenie: A dedicated ultrasonic scanner for acquiring RF echoes backscattered from the trabecular bone was developed. The design of device is based on the goal of minimizing of custom electronics and computations executed solely on the main computer processor and the graphics card. The electronic encoder-digitizer module executing all of the transmission and reception functions is based on a single low-cost field programmable gate array (FPGA). The scanner is equipped with a mechanical sector-scan probe with a concave transducer with 50 mm focal length, center frequency of 1.5 MHz and 60% bandwidth at −6 dB. The example of femoral neck bone examination shows that the scanner can provide ultrasonic data from deeply located bones with the ultrasound penetrating the trabecular bone up to a depth of 20 mm. It is also shown that the RF echo data acquired with the scanner allow for the estimation of attenuation coefficient and frequency dependence of backscattering coefficient of trabecular bone. The values of the calculated parameters are in the range of corresponding in vitro data from the literature but their variation is relatively high. Słowa kluczowe: cancellous bone, broadband ultrasound attenuation, FPGA Afiliacje autorów:
Litniewski J. | - | IPPT PAN | Cieślik L. | - | IPPT PAN | Lewandowski M. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Zienkiewicz B. | - | IPPT PAN | Nowicki A. | - | IPPT PAN |
| | 35p. |
8. |
Nowicki A., Lewandowski M., Wójcik J., Tymkiewicz R., Lou-Moller R.^{♦}, Wolny W.^{♦}, Zawada T.^{♦}, Thick Film Transducers for High Frequency Coded Ultrasonography,
ARCHIVES OF ACOUSTICS, ISSN: 0137-5075, Vol.36, No.4, pp.945-954, 2011Streszczenie: 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 transducers 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. Słowa kluczowe: transducers, thick film, high frequency ultrasound, pulse compression, Golay codes Afiliacje autorów:
Nowicki A. | - | IPPT PAN | Lewandowski M. | - | IPPT PAN | Wójcik J. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Lou-Moller R. | - | InSensor A/S (DK) | Wolny W. | - | InSensor A/S (DK) | Zawada T. | - | Ferroperm Piezoceramics A/S (DK) |
| | 15p. |
9. |
Secomski W., Nowicki A., Wójcik J., Lewandowski M., Walczak M., Tymkiewicz R., Annular array transducer and matched amplifier for therapeutic ultrasound,
ARCHIVES OF ACOUSTICS, ISSN: 0137-5075, DOI: 10.2478/v10168-010-0049-6, Vol.35, No.4, pp.653-660, 2010Streszczenie: 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 2.4W. Słowa kluczowe: ultrasonic therapy, annular array transducer, ultrasonic field Afiliacje autorów:
Secomski W. | - | IPPT PAN | Nowicki A. | - | IPPT PAN | Wójcik J. | - | IPPT PAN | Lewandowski M. | - | IPPT PAN | Walczak M. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN |
| | 9p. |
10. |
Nowicki A., Trots I., Lewin P.A.^{♦}, Secomski W., Tymkiewicz R., Influence of the ultrasound transducer bandwidth on selection of the complementary Golay bit code length,
Ultrasonics, ISSN: 0041-624X, DOI: 10.1016/j.ultras.2007.07.003, Vol.47, pp.64-73, 2007Streszczenie: In contrast to previously published papers [A. Nowicki, Z. Klimonda, M. Lewandowski, J. Litniewski, P.A. Lewin, I. Trots, Comparison of sound fields generated by different coded excitations – Experimental results, Ultrasonics 44 (1) (2006) 121–129; J. Litniewski, A. Nowicki, Z. Klimonda, M. Lewandowski, Sound fields for coded excitations in water and tissue: experimental approach, Ultrasound Med. Biol. 33 (4) (2007) 601–607], which examined the factors influencing the spatial resolution of coded complementary Golay sequences (CGS), this paper investigates the effect of ultrasound imaging transducer’s fractional bandwidth on the gain of the compressed echo signal for different spectral widths of the CGS. Two different bit lengths were considered, specifically one and two cycles. Three transducers having fractional bandwidth of 25%, 58% and 80% and operating at frequencies 6, 4.4 and 6 MHz, respectively were examined (one of the 6 MHz sources was focused and made of composite material). The experimental results have shown that by increasing the code length, i.e. decreasing the bandwidth, the compressed echo amplitude could be enhanced. The smaller the bandwidth was the larger was the gain; the pulse-echo sensitivity of the echo amplitude increased by 1.88, 1.62 and 1.47, for 25%, 58% and 80% bandwidths, respectively. These results indicate that two cycles bit length excitation is more suitable for use with bandwidth limited commercially available imaging transducers. Further, the time resolution is retained for transducers with two cycles excitation providing the fractional bandwidth is lower than approximately 90%. The results of this work also show that adjusting the code length allows signal-to-noise-ratio (SNR) to be enhanced while using limited (less that 80%) bandwidth imaging transducers. Also, for such bandwidth limited transducers two cycles excitation would not decrease the time resolution, obtained with ‘‘conventional’’ spike excitation. Hence, CGS excitation could be successfully implemented with the existing, relatively narrow band imaging transducers without the need to use usually more expensive wideband, composite ones. Słowa kluczowe: ultrasound imaging, transducer bandwidth, complementary Golay sequences Afiliacje autorów:
Nowicki A. | - | IPPT PAN | Trots I. | - | IPPT PAN | Lewin P.A. | - | Drexel University (US) | Secomski W. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN |
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11. |
Trots I., Nowicki A., Secomski W., Tymkiewicz R., The influence of the transducer bandwidth on the efficient Golay codes compression,
ARCHIVES OF ACOUSTICS, ISSN: 0137-5075, Vol.32, No.4, pp.101-110, 2007Streszczenie: The maximization of penetration depth with concurrent retaining or enhancement of image resolution constitutes one of the time invariant challenges in ultrasound imaging. To solve this problem a pulse compression technique employing long coded sequences is now under intensive investigation and in fact some of the corresponding techniques were already implemented in commercial scanning machines. This paper investigates the influence of the effective bandwidth of the transducer on the behaviour of the encoding/compression technique and its potential influence on the axial resolution. We have investigated two different bits lengths – one and two periods – in the Golay sequences resulting in substantial difference of the bandwidth of the transmitted sequences. Three transducers with different fractional bandwidths were used in the experiments: 6 MHz focused transducer with 25% fractional bandwidth, 4.4 MHz flat transducer with 58% fractional bandwidth and 6 MHz flat, composite transducer with 80% fractional bandwidth. The experimental results are clearly showing that the elongation of the Golay single bit length (two cycles in our case) compensates for the limited transducer bandwidth. For 25% bandwidth peak-to-peak echo increased by 1.89 times; for 58% bandwidth peak-to-peak echo amplitude increased by 1.62 times, and for 80% bandwidth peak-to-peak echo increased by 1.47 times. Słowa kluczowe: ultrasound imaging, transducer bandwidth, Golay complementary sequences Afiliacje autorów:
Trots I. | - | IPPT PAN | Nowicki A. | - | IPPT PAN | Secomski W. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN |
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12. |
Wójcik J., Powałowski T., Tymkiewicz R., Lamers A.^{♦}, Trawiński Z., Scattering of ultrasonic wave on a model of the artery,
ARCHIVES OF ACOUSTICS, ISSN: 0137-5075, Vol.31, pp.471-479, 2006Streszczenie: The study was aimed at elaboration of a mathematical model to describe the process of acoustic wave propagation in an inhomogeneous and absorbing medium, whereas the wave is generated by an ultrasonic probe. The modelling proces covered the phenomenon of ultrasonic wave backscattering on an elastic pipe with dimensions similar to the artery section. Later on the numerical codes were determined in order to calculate the fields of ultrasonic waves, as well as backscattered fields for various boundary conditions. Numerical calculations make it possible to definethe waveforms for electric signals that are produced when ultrasonic waves, being reflected and backsvattered by an artery model, are then received by the ultrasonic probe. It is the signalwhich pretty well corresponds with the actual RF signal that is obtained during measurements at the output of anultrasonic apparatus. Słowa kluczowe: ultrasound, backscattering, artery, numerical model Afiliacje autorów:
Wójcik J. | - | IPPT PAN | Powałowski T. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Lamers A. | - | inna afiliacja | Trawiński Z. | - | IPPT PAN |
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13. |
Nowicki A., Litniewski J., Secomski W., Trots I., Lewandowski M., Tymkiewicz R., Coded ultrasonography,
Annual Report - Polish Academy of Sciences, ISSN: 1640-3754, pp.56-57, 2005 | |
14. |
Filipczyński L., Wójcik J., Kujawska T., Łypacewicz G., Tymkiewicz R., Zienkiewicz B., Nonlinear Native Propagation Effect of Diagnostic Ultrasound Computed and Measured in Blood,
ULTRASOUND IN MEDICINE AND BIOLOGY, ISSN: 0301-5629, DOI: 10.1016/S0301-5629(00)00329-X, Vol.27, No.2, pp.251-257, 2001Streszczenie: Nonlinear propagation effects produced by focused pulses in blood were measured over a 20-cm range, being inspired by diagnostic applications in cardiology. The initial and maximum pressures applied during measurements in blood were equal to 0.40 MPapp and 0.76 MPapp, while the pressure estimated at the patient body surface equalled 0.70 MPapp. Measurements of the frequency characteristic and the linearity of the ultrasonic probe used in experiments were performed in water. A numerical procedure developed previously was applied in blood to calculate the pressure distribution of its first and second harmonics along the beam axis. The comparison of numerical and measured distributions in blood at a temperature of 37°C showed rather good agreement. Using numerical methods, a proportional growth of the second harmonic with the increased applied initial pressure was first observed, and finally the maximum limiting effect was found. In this way, much higher level of harmonics could be obtained. However, there arise the questions of the transmitting system construction and of the nonuniform resolution in the case of harmonic imaging when increasing the applied initial pressure. Słowa kluczowe: Ultrasound, Pulses, Nonlinear propagation, Blood, Cardiology Afiliacje autorów:
Filipczyński L. | - | IPPT PAN | Wójcik J. | - | IPPT PAN | Kujawska T. | - | IPPT PAN | Łypacewicz G. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Zienkiewicz B. | - | IPPT PAN |
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15. |
Filipczyński L., Kujawska T., Wójcik J., Tymkiewicz R., Numerical and experimental pressure determination in the very near field of a piezoelectric transducer,
ARCHIVES OF ACOUSTICS, ISSN: 0137-5075, Vol.26, No.3, pp.223-233, 2001Streszczenie: Measurements in the very near field of piezoelectric transducers are fundamental for many ultrasonic problems. In such cases also the transducer vibrations should be known to perform mathematical models of radiated beams. Acoustic pressure measurements near to the transducer surface can give the necessary information. The pressure of the radiated wave at the transducer surface corresponds to its normal vibration velocity multiplied by the [ampersand]rho;c value of the medium. However, this is valid only for the central wave, when the edge wave of the transducer can be ignored. On the other hand, pressure measurements on and very near to the transducer surface are not possible because of the voltage leakage between the electronic transmitter and the PVDF hydrophone used in such measurements. By means of a numerical model, central and edge waves were found for a plane PZT transducer 7.5mm in radius, with the applied 2.7MHz voltage pulse composed of 3 cycles. Two types of boundary conditions of Dirichlet and Neumann were considered showing a negligible difference in the case of short pulses. Basing on numerical and experimental results, practical conditions were determined which make it possible to carry out pressure measurements in the very near field of the transducer, and hence to determine the transducer vibrations which are important for modeling ultrasonic pulse beams. Afiliacje autorów:
Filipczyński L. | - | IPPT PAN | Kujawska T. | - | IPPT PAN | Wójcik J. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN |
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16. |
Filipczyński L., Kujawska T., Tymkiewicz R., Wójcik J., Nonlinear and linear propagation of diagnostic ultrasound pulses,
ULTRASOUND IN MEDICINE AND BIOLOGY, ISSN: 0301-5629, DOI: 10.1016/S0301-5629(98)00174-4, Vol.25, No.2, pp.285-299, 1999Streszczenie: The effect of nonlinear propagation in fluid followed by soft tissue was studied both theoretically and experimentally for a most crucial case in obstetrical ultrasonography. For this purpose, short pressure pulses, with the duration time of 1.3 μs and a carrier frequency of 3 MHz, radiated by a concave transducer into water, with maximum intensities up to the value of 18 W/cm2, were computed and measured. The ultrasonic beam had the physical focus at the distance of 6.5 cm, where the highest focal intensity of ISPPA= 242 W/cm2 was obtained. In front of the transducer, at a distance of 7 cm, artificial tissue samples prepared on the basis of ground porcine kidney, with a thickness of 0.5, 1.5 and 3 cm, were placed in water. Pressure pulses and their spectral components were produced numerically and measured by means of a PVDF hydrophone in water before and after penetrating the tissue samples. The theoretical analysis and measurements were carried out, in every case, for two signal levels: for a high level assuring nonlinear propagation and for a low one where conditions of linear propagation were fulfilled. In this way, it was possible to compare directly the effects of nonlinear and linear propagation, in every case showing a good conformity of theoretical values with measured ones. A method of determination of the effective frequency response of the hydrophone was elaborated to enable quantitative comparisons of numerical and experimental results. The theoretical part of our study was based on a paper of Wójcik (1998), enabling us to compute the characteristic function of nonlinear increase of absorption. An agreement of up to 10% was obtained when comparing theoretical and measured values of these functions in the investigated beam in water and behind tissue samples. The results obtained showed that the recently given theory of nonlinear absorption, based on the spectral analysis and the elaborated numerical procedures, may be useful in various practical ultrasonic medical problems and also in technological applications. Słowa kluczowe: Ultrasound, Pulses, Nonlinear propagation, Diagnostics Afiliacje autorów:
Filipczyński L. | - | IPPT PAN | Kujawska T. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Wójcik J. | - | IPPT PAN |
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17. |
Filipczyński L., Kujawska T., Tymkiewicz R., Wójcik J., Amplitude, isobar and gray -scale imaging of ultrasonic shadows behind rigid, elastic and gaseous spheres,
ULTRASOUND IN MEDICINE AND BIOLOGY, ISSN: 0301-5629, DOI: 10.1016/0301-5629(95)02031-4, Vol.22, No.2, pp.261-270, 1996Streszczenie: The theory of wave reflection from spherical obstacles was applied for determination of the cause of the shadow created by plane wave pulses incident on rigid, steel, gaseous spheres and on spheres made of kidney stones. The spheres were immersed in water which was assumed to be a tissuelike medium. Acoustic pressure distributions behind the spheres with the radii of 1 mm, 2.5 mm and 3.5 mm were determined at the frequency of 5 MHz. The use of the exact wave theory enabled us to take into account the diffraction effects. The computed pressure distributions were verified experimentally at the frequency of 5 MHz for a steel sphere with a 2.5-mm radius. The experimental and theoretical pulses were composed of about three ultrasonic frequency periods. Acoustic pressure distributions in the shadow zone of all spheres were shown in the amplitude axonometric projection, in the grey scale and also as acoustic isobar patterns. Our analysis confirmed existing simpler descriptions of the shadow from the point of view of reflection and refraction effects; however, our approach is more general, also including diffraction effects and assuming the pulse mode. The analysis has shown that gaseous spherical inclusions caused shadows with very high dynamics of acoustic pressures that were about 15 dB higher in relation to all the other spheres. The shadow length, determined as the length at which one observes a 6-dB drop of the acoustic pressure, followed the relation r−6dB = 3.7a2λ with the accuracy of about 20% independent of the sphere type. λ denotes the wavelength and a the sphere radius. Thus, a theoretical possibility of differentiating between gaseous and other inclusions and of estimation of the inclusion size in the millimeter range from the shadow was shown. The influence of the frequency-dependent attenuation on the shadow will be considered in the next study. Słowa kluczowe: Shadow, Pulses, Spheres, Ultrasonography Afiliacje autorów:
Filipczyński L. | - | IPPT PAN | Kujawska T. | - | IPPT PAN | Tymkiewicz R. | - | IPPT PAN | Wójcik J. | - | IPPT PAN |
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