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1
Content available Comparison of experimental results and numerical calculations of ultrasonic waves scattering on a model of the artery
Wójcik J., Trawiński Z., Powałowski T.
Hydroacoustics
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2008
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Vol. 11
449-458
EN
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.
2
Numerical analyze and experimental results of ultrasonic waves scattering on a model of the artery
Wójcik J., Powałowski T., Trawiński Z.
Molecular and Quantum Acoustics
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2007
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Vol. 28
279-283
EN
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 5 mm and wall thickness of 1.25 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 good agreement between the numerical calculation and experimental results was obtained.
3
Content available Numerical solver of acoustic field in simulation of artery wall thickness examinations
Powałowski T., Wójcik J., Trawiński Z.
Hydroacoustics
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2007
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Vol. 10
163-168
EN
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.
4
Content available remote Modelling of examinations of artery wall thickness changes
Powałowski T., Wójcik J., Trawiński Z.
Archives of Acoustics
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2007
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Vol. 32, No. 4
851--857
EN
The developed solver of acoustic field was used for simulation of the artery wall thickness examination. It is capable of describing spatial and time-dependent distribution of an ultrasonic beam, that is emitted by a piezoelectric ring transducer and then backscattered on cylindrical surfaces of the walls in artery models. The electrical signal received corresponds closely with the actual RF signal that is obtained during measurements at the output of the ultrasonic VED apparatus. The theoretical model of the artery for creating the ultrasonic reflected echoes was used. The internal radius of the artery model was equal 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 echoes-tracking solver based on the zero-crossing and correlation methods was used for detecting changes of the IMT.
5
Content available remote Scattering of ultrasonic wave on a model of the artery
Wójcik J., Powałowski T., Tymkiewicz R., Lamers A., Trawiński Z.
Archives of Acoustics
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2006
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Vol. 31, No. 4
471-479
EN
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 process 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 define the waveforms for electric signals that are produced when ultrasonic waves, being reflected and backscattered by an artery model, are then received by the ultrasonic probe. It is the signal which pretty well corresponds with the actual RF signal that is obtained during measurements at the output of an ultrasonic apparatus.
6
Content available remote Non-invasive ultrasonic examination of the local pulse wave velocity in the common carotid artery
Powałowski T., Trawiński Z.
Archives of Acoustics
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2004
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Vol. 29, no. 4
597-606
EN
Local pulse wave velocity (PWV) is one of important indicators of artery wall's elastic properties. This paper describes a non-invasive method of examinations of local PWV on the basis of ultrasonic blood flow velocity measurements at two points, several centimetres along the common carotid artery (CCA). This velocity was compared with values of PWV calculated on the basis of measurement of distensibility coefficient DC. The examinations were carried out on the group of 12 healthy volunteers ranging in age from 22 to 68 years (mean 39š16 years). Mean value of local PWV for the examined group was 5.1š1.09 m/s. This velocity was linearly correlated (r = 0.9807) with the PWV examined on the basis of distensibility coefficient DC, the mean value of which was 6.14š1.29 m/s.
7
Content available remote Ultrasonic examination of common carotid artery wall elasticity of persons with different stages of internal carotid artery atherosclerosis
Powałowski T., Trawiński Z., Hilgertner R.
Archives of Acoustics
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2003
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Vol. 28, no. 4
325-337
EN
Ultrasonic methods were used in this study to examine the association between the common carotid artery (CCA) wall elasticity and the atherosclerosis stage in the internal carotid artery (ICA). The degree of stenosis determined ultrasongraphically was used as an indicator of the atherosclerosis stage in the ICA. The examined persons were 45 to 80 years old. They had no arterial hypertension, diabetes mellitus and were not smokers. A comparative study was carried out for cases with ICA atherosclerosis (66 arteries) and without ICA atherosclerosis (61 arteries). In both groups there were persons without and with hypercholesterolemia, which according to our studies had no significant influence on CCA wall elasticity. The CCA wall elasticity was determined by the stiffness coefficient alpha and the distensibility coefficient DC based on ultrasonic measurements. The influences of age and arterial blood pressure on the CCA wall elasticity were taken into account in the analysis. The study revealed a significant decrease of the CCA wall elasticity in the case of patients with atherosclerosis compared with persons without atherosclerosis, and showed a significant correlation between the increase of the ICA stenosis degree and the decrease of CCA wall elasticity.
8
Ultradźwiękowe badanie wejściowej impedancji w modelach rozgałęzienia tętnicy szyjnej wspólnej
Powałowski T., Kałużyński K., Trawiński Z., Leśniak B.
Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje
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2001
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Vol. 83, nr 27
355-360
EN
The paper presents the setup and the results of examinations of the input impedance in the silicon models of the common carotid artery bifurcation without stenosis and with 90 % stenosis of the internal carotid artery branch. The input impedance measured in the models is compared with impedance calculated on the base of the values of the hydraulic model elements and of the model load. As a criterion of determination is used the difference between the measured flow and the flow evaluated on the basis on the calculated impedance in the carotid artery bifurcation models. There was no significant difference between the measured and calculated input impedances in the ease of the non-stenosed internal carotid artery. A significant difference between measured and calculated impedances was found for the model of bifurcation with the stenosis of the internal carotid artery. Reflections of pressure wave from the stenosis are expected to be the reason of this effect.
9
Content available remote Analysis or vascular input impedance in the common carotid artery measured by means or ultrasound
Powałowski T.
Biocybernetics and Biomedical Engineering
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2001
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Vol. 21, no. 3
101-115
EN
The paper presents the results of analysis of vascular input impedance noninvasively determined in the common carotid artery in healthy persons and persons with atherosclerosis in the internal carotid artery. The vascular input impedance was evaluated by simultaneous measurements of blood flow velocity and blood pressure employing the Doppler ultrasound and echo tracking methods. The examinations were performed using the ultrasonic equipment VED which was designed at the Ultrasonic Department of the Institute of Fundamental Technology Research, Polish Academy of Science in Warsaw. The results of measuring vascular input impedance were compared with the extent of stenosis in the internal carotid artery, evaluated through a joint ultrasonography and Doppler examination, and the volumetric velocity and values of the resistance RI and pulsatility PI indexes evaluated by measuring linear blood flow velocity. Analysis of the vascular input impedance was based on a four-element substitution lumped parameters model of the vascular system. The particular elements represented inertance L, vessel compliance C, vessel resistance Ro in the main arteries and peripheral resistance Rp in small vessels. The values of these elements were determined by computer simulation of vascular input impedance using the input impedance of the model. Analysis of the vascular input impedance showed that for internal carotid artery stenosis exceeding 30% the value of resistance Ro was significantly greater than in healthy persons. For internal carotid artery stenosis of 30% to 74% the value of Ro/ Rp ratio increased while the average blood flow remained the same (as a result of autoregulation in cerebral circulation system). For this range of stenosis, the PI and RI index values showed no significant difference from the healthy control group. In the range of autoregulation in cerebral circulation system the results point to the non-invasive measurements of the vascular input impedance in the common carotid artery as being a much more sensitive indication of the occurrence of atherosclerotic stenosis in the internal carotid artery than the resistance RI and pulsatility PI indexes that have so far been applied.
PL
W pracy przedstawiono wyniki analizy wejściowej impedancji naczyniowej wyznaczanej nieinwazyjnie w tętnicy szyjnej wspólnej u osób zdrowych i osób ze zmianami miażdżycowymi w tętnicy szyjnej wewnętrznej. Wejściowa impedancja naczyniowa wyznaczana była na podstawie równoczesnych pomiarów prędkości przepływu krwi i ciśnienia krwi przy zastosowaniu ultradźwiękowej metody dopplerowskiej i metody śledzenia echa. Badania przeprowadzono za pomocą aparatu ultradźwiękowego VED opracowanego w Zakładzie Ultradźwięków Instytutu Podstawowych Problemów Techniki, Polskiej Akademii Nauk w Warszawie. Wyniki badań wejściowej impedancji naczyniowej odnoszono do stopnia zwężenia tętnicy szyjnej wewnętrznej określonego na podstawie połączonego badania ultrasonograficznego i dopplerowskiego oraz do prędkości objętościowej krwi i wartości indeksów oporowego RI i pulsacji PI wyznaczonych na podstawie pomiaru prędkości liniowej przepływu krwi. Analiza wejściowej impedancji naczyniowej przeprowadzona była na podstawie czteroelementowego modelu zastępczego układu naczyniowego o stałych skupionych. Elementy modelu reprezentowały inertancję L, podatność układu naczyniowego C, opór naczyniowy w głównych naczyniach tętniczych Ro i opór peryferyjny Rp w małych naczyniach krwionośnych. Elementy te wyznaczane były na drodze symulacji komputerowej wejściowej impedancji naczyniowej za pomocą impedancji wejściowej modelu. Analiza wejściowej impedancji wykazała, że dla przedziału zwężeń tętnicy szyjnej wewnętrznej powyżej 30%, wartość oporu Ro była znacząco większa, w porównaniu z tą wartością u osób zdrowych. Dla przedziału zwężeń od 30% do 74% wartość stosunku Ro/Rp rosła podczas gdy średni przepływ krwi nie ulegał zmianie, co spowodowane było działaniem systemu autoregulacji w krążeniu mózgowym. Dla tego przedziału zwężeń nie zaobserwowano również znamiennej różnicy w wartościach indeksów PI i RI w stosunku do grupy kontrolnej osób zdrowych. Uzyskane wyniki badań wskazują, że dla zakresu działania systemu autoregulacji w krążeniu mózgowym wejściowa impedancja naczyniowa wyznaczana nieinwazyjnie w tętnicy szyjnej wspólnej jest znacznie czulszym wskaźnikiem występowania zwężeń tętnicy szyjnej wewnętrznej na tle miażdżycowym niż stosowane do tej pory indeksy: oporowy RI i pulsacji PI.
10
Content available remote Common carotid wall elasticity and intima-media thickness examinations by means of ultrasound
Powałowski T., Hilgertner R., Trawiński Z.
Archives of Acoustics
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2000
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Vol. 25, no. 2
205-212
EN
The aim of this study was to examine the relation between the intima-media thickness and the wall elasticity measured simultaneously in the same cross-section of the common carotid artery. A group of 40 persons (19 healthy and 21 with hypertension and/or atherosclerosis) aged 22 to 81 were diagnosed by means of ultrasound. A high correlation occurred between the wall stiffness coefficient [alpha] and the intima-media thickness (r=0.950, p<0.00001)
11
Content available remote Analysis of blood pressure wave in the human common carotid artery on the basis of non-invasive ultrasonic examinations
Powałowski T.
Archives of Acoustics
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2000
|
Vol. 25, no. 2
191-204
EN
The aim of the study was the examination of the forward and reflected blood pressure waves in the common carotid artery on the basis of non-invasive ultrasonic examinations. The study concerned the effect of stenosis of the internal carotid artery caused by atherosclerosis on the mean reflection coefficient modulus and the time delay between the reflected blood pressure wave and the forward blood pressure wave. The investigations were carried out on a group of healthy persons (30 cases) and on a group of sick persons (17 cases) with stenosis or occlusion of the internal carotid artery.
12
Content available Common carotid wall elasticity and intima-media thickness examinations by means of ultrasound
Powałowski T., Hilgertner L., Trawiński Z.
Hydroacoustics
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1997
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Vol. 1
343--346
EN
The aim of this study was to examine the relation between the intima-media thickness and the wall elasticity in the common carotid artery. A group of 40 persons (19 healthy and 21 with hypertension and/or atherosclerosis) aged 22 to 81 were diagnosed by means of ultrasound. A high correlation occurred between the wall stiffness coefficient α and the intima-media thickness (r = 0.950, p<0.001).
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