Instytut Podstawowych Problemów Techniki

Streszczenie:

The aim of this paper is to present the new method for relative changes measurements of intima-media thickness in the common carotid artery wall. The numerical solver was created for calculation of the fields of ultrasonic beams and scattered fields under different boundary conditions and different angles of penetration of ultrasonic beams with respect to the position of the arterial wall. The cylindrical model of the artery was changing the radius and thickness of the wall under cyclic variation of blood pressure. The presented method was verified on a pipe made of latex. The paper describes also the initial results of examinations of the intima-media thickness. The good agreement for the angle dependence and the perpendicular ultrasonic beam displacement from the longitudinal axis of the artery segment between the numerical calculation and experimental results was obtained for different artery diameters.

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Streszczenie:

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.

Słowa kluczowe:

Model of the artery, scattering, numerical solver

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Streszczenie:

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.

Słowa kluczowe:

ultrasound, scatering, artery model, numerical calculations, eksperimental results, Comparison

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Streszczenie:

The paper describes the initial results of examinations of the intima-media thickness (IMT) in the common carotid artery wall. The examinations of the IMT enable the assessment of elastic properties of the arterial wall. Ultrasonic examinations were carried out on healthy volunteers with the use the apparatus Vascular Echo Doppler (VED), designed by the authors to measure the elasticity of arteries. Application of the PDA-14 PC-card (Signatec) allowed for the acquisition of ultrasonic RF signal from the output of the apparatus VED and further analysis of dynamic changes of the IMT during a heart cycle. Changing of the IMT in time as a difference between the instantaneous position of the two tracking slopes of RF echoes was obtained. For this purpose, the zero-crossing method for tracking the phase changes of the two rising slopes of the RF ultrasonic echo was used.

Słowa kluczowe:

ultrasound, common carotid artery, elasticity, intima-media thickness

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Streszczenie:

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 ultrasonicVED apparatus. The theoretical model of the artery for creating the ultrasonic reflected echoes was used. The internal radius of the artery model was 3mm for the diastolic pressure and 3.3mm for the systolic pressure. The intima- media thicknes (IMT) of the artery wall was changed from 0.48mm to 0.44mm respectively. The echoes-tracking solver based on the zero-crossing and correlation methods was used for detecting changes of the IMT.

Słowa kluczowe:

ultrasound, common carotid artery, elasticity, intima-media thickness, numerical solver

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Streszczenie:

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 anultrasonic apparatus. The developed solver of acoustic field was used for simulation of the artery wall tickness examination. The theoretical model of the atrery for the creating the simulated ultrasonic reflected echoes was used. The internal radiusof the artery model was 3mm for the diastolic pressure and and 3.3mm for the systolic pressure. The intima-media thicknes (IMT) of the artery wall was changed from o.48 to 0.44 respectively. The solver based on zero-crossing method was used for detecting changes of the IMT.

Słowa kluczowe:

ultrasound, mathematical model, scatering, inhomogenous loosing medium, numerical simulations, intima-media changes

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Streszczenie:

The paper describes the initial results of numeric analysis of plane-strain of a model of the human common carotid artery. The results of computer modeling were compared with the experimental data obtained by means of ultrasonic measurements of the changes in the thickness of the common carotid artery wall. The ultrasonic examination was carried out on a 34 years old healthy male using the VED apparatus designed by the authors to measure the elasticity of arteries. The numeric analysis was made by means of the finite element method (FEM) using the MARC K7 programming of the Analysis Research Corporation based on the operating system UNIX. As a model of the common carotid artery the authors used a hollow cylinder made of the isotropic, homogeneous, almost incompressible material (Poisson’s constant ν=0.4999) having the Young’s module E=159.2 kPa and the combined thickness of the internal and middle layer IMT = 0.52 mm. The modeling of plane-strain concerned the effect of the change in the internal radius and the change in the cylinder wall thickness as a result of the static change of pressure inside the cylinder within the values of 0–45 mmHg. The study obtained satisfactory results in the computer simulation of the changes in the artery walls thickness.

Słowa kluczowe:

ultrasound, elasticity of the common carotid artery wall, wall thickness

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Streszczenie:

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

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Streszczenie:

Examination of the carotid artery stenosis is very important in the diag-nosis of cerebrovascular diseases. New possibilities in the diagnosis of stenotic lesions are provided by ultrasonic Doppler angiography. The aim of this paper is to present a Doppler imaging system developed by the authors for the exami¬nation of blood flowing in carotid arteries. The system is based upon a 5 MHz bi-directional c.tv. Doppler flowmeter with a separate output for anterograde and retrograde flows. A special bank of filters converts signals into various levels of the gray-scale display which correspond to the value of the blood flow velocity. The ultrasonic probe is held by the scanning arm. The position of the probe on the skin of the patient is electronically sensed by the position-sensing circuity which causes the bright spot on the image display to move according to the position of the probe. The Doppler image from the artery is stored in a digital memory system. The clinical results obtained by means of this system showed good agreement with X-ray arteriography for obstructions occluding more than 50 per cent of the arterial diameter.

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Streszczenie:

The authors present results of quantitative measurements of blood in vivo in the carotid artery of man. The Doppler pulse technique was used after being previously verified for steady state flows in tubes and for pulsating flows in a canine aorta where the electromagnetic method was also used for comparison.

An ultrasonic probe with two transducers was adapted for determination of the angle of the ultrasonic beam in relation to the vessel allowing the measurement of the vessel diameter which was also determined by means of the ultrasonographic B-mode technique.

By means of the Doppler pulse method profiles of the blood velocity in the carotid artery were determined as a function of time.

The continous wave Doppler technique together with the zero-crossing system and spectral analysis were also used for making measurements.

The flow velocity and the shape of the flow curve with time obtained with the above techniques showed good agreement. The measured flow rate in the carotid artery amounted to QM = 1.61/min (maximum instantaneous value) and Q0 - 0.531/min (mean time value).

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