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1

Remote visualization of the velocity distribution on vibrating structures using the wave field analysis

Lewin P. A., Berger A. W., Vecchio C. J., Schafer M. E.

Mechanics / AGH University of Science and Technology

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2007

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Vol. 26, no. 2

55-59

EN

Knowledge of vibrating pattern characteristics is of interest in many applications, including minimization of noise generation in different media and design and optimization of piezoelectric transducers used in diagnostic ultrasound imaging. A field expansion technique developed for analyzing the acoustic fields and vibrating structures is presented. The technique is based on the angular spectrum method of wave-field analysis, and is applicable to both continuous (CW) and wideband pulsed waves, and allows the effects of acoustic parameters such as absorption, dispersion, refraction, and phase distortion to be accounted for. Examples of remotely reconstructed surface velocity distributions of complex acoustic radiators are presented and the potential applications of the technique developed in the analysis of fields radiated by sources with arbitrary geometries, including arrays are also pointed out.

PL

Wiedza o charakterystyce wzorów drgań znajduje się w obrębie zainteresowania wielu aplikacji, włączając w to minimalizację generacji hałasu w różnych środowiskach oraz projektowanie i optymalizację przetworników piezoelektrycznych używanych do obrazowania w diagnostyce ultradźwiękowej. Zaprezentowano obszar rozwijającej się techniki do analizy pola akustycznego i drgających obiektów. Technika ta bazuje na metodzie spektralnej analizy pola fali za pomocą obciętych szeregów Fouriera i jest stosowana zarówno do ciągłych, jak i szerokopasmowych fal impulsowych, pozwalając na wyliczenie parametrów akustycznych takich, jak pochłanianie, rozpraszanie, załamanie i zniekształcenie fazy. Wyszczególniono również przykłady zdalnie zrekonstruowanych rozkładów pól prędkości złożonych promienników akustycznych oraz potencjalne możliwości zastosowań rozwijanej techniki w analizie pól promieniujących ze źródeł o określonej geometrii; włączając struktury macierzowe.

2

Non-invasive measurement of blood hematocrit in artery

Secomski W., Nowicki A., Guidi F., Tortoli P., Lewin P.A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2005

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Vol. 53, nr 3

245-250

EN

Objective: The goal of this work was to develop a clinically applicable method for non-invasive acoustic determination of hematocrit m VIVO. Methods: The value of hematocrit (HCT) was determined initially in vitro from the pulse-echo measurements of acoustic attenuation. The testing was carried out using a laboratory setup with ultrasound transducer operating at 20 MHz and employing human blood samples at the temperature of 37°C. The attenuation coefficient measurements in blood in vitro and in vivo were implemented using multi-gated (128-gates), 20 MHz pulse Doppler flow meter. The Doppler signal was recorded in the brachial artery. Both in vitro and in vivo HCT data were compared with those obtained using widely accepted, conventional centrifuge method. Results: The attenuation coefficient in vitro was determined from the measurements of 168 samples with hematocrit varying between 23.9 and 51.6%. Those experiments indicated that the coefficient increased linearly with hematocrit. The HCT value was obtained from the 20 MHz data using regression analysis. The attenuation (0 was determined as a 42.14 + 1.02 . HCT (Np/m). The corresponding standard deviation (SD), and the correlation coefficient were calculated as SD = 2.4 Np/m, and R = 0.9, (p < 0.001 ), respectively The absolute accuracy of in vivo measurements in the brachial artery was determined to be within +-5% HCT. Conclusions: The method proposed appears to be promising for in vivo determination of hematocrit as 5% error is adequate to monitor changes in patients in shock or during dialysis. It was found that the multigate system largely simplified the placement of an ultrasonic probing beam in the center of the blood vessel. Current work focuses on enhancing the method's applicability to arbitrary selected vessels and reducing the HCT measurement error to well below 5%.

3

Direct and post-compressed sound fields for different coded excitations - experimental results

Klimonda Z., Lewandowski M., Nowicki A., Trots I., Lewin P. A.

Archives of Acoustics

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2005

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Vol. 30, No. 4

507-514

EN

Coded ultrasonography is intensively studied in many laboratories due to its remarkable properties: increased depth penetration, signal-to-noise ratio (SNR) gain and improved axial resolution. However, no data concerning the spatial behavior of the pressure field generated by coded bursts transmissions were reported so far. Five different excitation schemes were investigated. Flat, circular transducer with 15 mm diameter, 2 MHz center frequency and 50\% bandwidth was used. The experimental data was recorded using the PVDF membrane hydrophone and collected with computerized scanning system developed in our laboratory. The results of measured pressure fields before and after compression were then compared to those recorded using standard ultrasonographic short-pulse excitation. The increase in the SNR of the decoded pressure fields is observed. The modification of the spatial pressure field distribution, especially in the intensity and shape of the sidelobes is apparent. Coded sequences are relatively long and, intuitively, the beam shape could be expected to be very similar to the sound field of long-period sine burst. This is true for non-compressed distributions of examined signals. However, as will be shown, the compressed sound fields, especially for the measured binary sequences, are similar rather to field distributions of short, wideband bursts.

4

Nonlinear equations of acoustics - numerical solutions and their visualization

Wójcik J., Lewin P. A., Nowicki A., Filipczyński L., Kujawska T., Radulescu E.

Hydroacoustics

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2003

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Vol. 6

137--142

EN

The novel effective numeric solver of the nonlinear scalar wave equation describing the acoustic wave propagation in the attenuating media was derived. The solver was developed for the PC environment. The standard computation data include al! stationary and dynamic characteristics of the radiated ultrasonic pressure field, especially its 4D (space/time) visualization. The results obtained with the solver can be used as the supporting tools (tool) in designing and developments of the multielement linear and phase array transducers applied in ultrasonography.

5

On the application of signal compression using Golay's codes sequences in ultrasound diagnostic

Nowicki A., Secomski W., Litniewski J., Trots I., Lewin P. A.

Archives of Acoustics

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2003

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Vol. 28, no. 4

313-324

EN

The issue of maximizing penetration depth with concurrent retaining or enhancement of image resolution constitutes one of the time invariant challenges in ultrasound imaging. Concerns about potential and undesirable side effects set limits on the possibility of overcoming the frequency dependent attenuation effects by increasing peak acoustic amplitudes of the waves probing the tissue. To overcome this limitation a pulse compression technique employing 8 bits Complementary Golay Code (CGS) was implemented at 4 MHz. In comparison with other, earlier proposed, coded excitation schemes, such as chirp, pseudo-random chirp and Barker codes, the CGS allowed virtually side lobe free operation. Computer simulation results for CGS pulse compression are presented. Next, the images of RMI tissue phantom generated by those two excitations schemes are presented. Identical peak power conditions in the experimental setup were implemented with the earlier mentioned 8 bits CGC and 2 periods tone burst. Experimental data indicate that the quality of CGS images is comparable to that acquired using conventional pulse imaging. CGS exhibited signal-to-noise ratio (SNR) gain of 9.6 dB with the axial resolution being virtually the same for both transmitting schemes.

6

Acoustic output levels and ultrasound output display standard

Lewin P. A., Nowicki A.

Archives of Acoustics

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1998

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Vol. 23, no. 2

267-280

EN

This paper discusses rationale behind the development of output display standard (ODS) and points out its clinical implications. Physical mechanisms of interaction between ultrasound and biological tissue are reviewed and basic ultrasound field parameters needed to understand and appreciate the impact of Mechanical Index (MI) and Thermal Index (TI) on clinical practice are introduced. Definition of indices is presented and their dependence on acoustic field generated by the scanning probes is discussed. The applicability of MI as an predictor of the potential mechanical effects in B-mode imaging and TI's relevance in Doppler, M-mode and color flow imaging is indicated. Three different tissue models, namely, homogeneous and layered, and bone/tissue interface are presented in detail and the influence of each of the models on the potential temperature increase prediction is stressed. The importance of implementation of ALARA (As Low As Reasonably Achievable) principle is also noted out.