Noriyoshi Chubachi

Accuracy Evaluation in the Measurement of a Small Change in the Thickness of Arterial Walls and the Measurement of Elasticity of the Human Carotid Artery

For the diagnosis of the early stages of atherosclerosis, it is important to evaluate the local acoustic characteristics of the arterial wall. For this purpose, it is necessary to increase the spatial resolution in the axial direction to several millimeters, which corresponds to the size of the macular lesion on the surface of the wall. We have proposed a method for measuring small velocity signals on the intima and adventitia of the arterial wall from the skin surface using pulsive ultrasonic waves. The small change in thickness of the arterial wall is obtained by integrating the difference between the two velocity signals on the intima and adventitia. The elastic property of the arterial wall is noninvasively evaluated from the change in thickness and the arterial inner pressure. In this paper, we evaluate the accuracy of the proposed method for measuring the small displacement. Moreover, we applied this method to evaluate the elastic property of the arterial wall of 50 patients and 8 healthy subjects.

Measurement of local pulse wave velocity in arteriosclerosis by ultrasonic Doppler method

This paper presents a new method to measure local pulse wave velocity (PWV), which is an index of the hardness in the range of several millimeters on the aortic wall for diagnosis of the early stage arteriosclerosis. Small vibration signals are measured simultaneously at two adjacent points on the aortic wall near the aortic valve by electronically alternating the direction of an ultrasonic beam. Transit delay time of the pulse wave between these two points is determined from the two vibration signals obtained by this alternating-beam method. Local PWV at a point several millimeters along the aorta is precisely obtained by dividing distance between these points by resultant transit delay time. Such local acoustic properties of the blood vessels will prove useful, especially for noninvasive diagnosis of early stage arteriosclerosis

Measurement of local elasticity of human carotid arterial walls and its relationship with risk index of atherosclerosis

We have proposed a new method for evaluating the local elasticity of the arterial wall in order to diagnose the early stage atherosclerosis. In the case of the early stage atherosclerosis, the macular lesion is several millimeters in diameter. Therefore, it, is necessary to find the local change in the elasticity of the arterial wall. In the proposed method, the small change in thickness of the arterial wall during cardiac cycle is accurately measured using ultrasound, and the elasticity of the arterial wall can be evaluated in every small region of about 1 millimeter, which corresponds to the width of the ultrasonic beam. In the report, the proposed method is applied to human carotid arteries of 54 male patients and 30 healthy male subjects, where the patients have high risk factor of coronary heart diseases. From this results, the difference in the elasticity of the arterial walls between healthy subjects and patients is investigated.

Design of the Double Ultrasonic Transducer for Nonlinearity Measurement of Acoustic Waves

In this paper, we propose and design a new ultrasonic probe that can effectively measure both the fundamental and the second-harmonic waves simultaneously. The transducer consists of two bonded Pb(Zr, Ti)O3 (PZT) disks with the same properties and the same polarization, and a variable capacitor is connected to the electric terminals of one of the PZT disks for the simulation and experiment. It is shown that the second harmonic as well as the fundamental component can be efficiently received by controlling the capacitance. The result of the nonlinearity parameter B/A for ethanol measured using the double ultrasonic transducer shows good agreement with the reference value, and the B/A value for soybean is obtained.

Imaging spatial distribution of high-frequency small vibrations on the heart wall

We have developed a novel method for accurately measuring the velocity signals on the multiple points preset on an ultrasonic beam in the heart wall by tracking the movement of the heart wall. By applying the time-frequency analysis to the resultant velocity signals of the heart wall, we have determined the instantaneous eigenfrequency of the left ventricle (LV) at the end-diastole. From the eigenfrequency, the wall thickness of the LV, the average radius of the LV, and the inner pressure of the LV, are noninvasively estimated at the end-diastole using a model of an elastic spherical shell. For this measurement, however, it is necessary to confirm the mode of the eigenvibration in the LV. In this report, therefore, we control the directions of the ultrasonic beams so that the velocity signals are simultaneously measured at the multiple points on the surface of the LV wall. From these data, we estimate the spatial distribution of the eigenvibration of the LV wall at the end-diastole.

A Novel Method of Estimating the Aspect Ratio of Pipe Wall Thickness to Diameter Utilizing the Characteristics of a Hollow Cylindrical Guided Wave

We have developed a method of estimating the aspect ratio of a pipe wall thickness to diameter (t/d) using a hollow cylindrical guided wave (HCGW). The HCGW is an ultrasonic guided wave in a pipe. The method is very useful for onsite and nondestructive estimation of pipe wall thickness. It is based on the change of the dispersion relation of the HCGW as a function of t/d. The group velocity of the primary wave (first arriving wave packet from an impulse source) of the HCGW ranges from the bar velocity to the sheet velocity as a function of t/d. The bar velocity is the velocity of the DC component of the guided wave propagating in a solid cylinder; the sheet velocity is that of the S0 mode Lamb wave. The first part of the paper describes the principle of the method. In the last part, a laser ultrasonic method was employed to verify the method in both time- and time-frequency domains. The experimental results for aluminum pipes with various t/d’s were in good agreement with the theory.Copyright

Beam-Width-Controllable Ultrasonic Transducer Array

In this paper, we present a new method for beam width control of transducer array using two-layered piezoelectric transducers of which electroacoustic efficiency can be controlled by a capacitor. The measured result for beam width control of the transducer array shows good agreement with the simulation result. It is confirmed that the beam width of the transducer array is easily controlled by varying the second harmonic generation efficiency of each element.

In vivo Measurement Method for Nonlinearity Parameters Using Single Ultrasonic Transducer

A transducer consisting of two bonded Pb(Zr, Ti)O3 (PZT) disks is applied to measure the nonlinearity distribution in a layered biological tissue and an in vivo measurement method using the transducer is also investigated. The measured results of nonlinearity parameters of B/A are compared with the theoretical results calculated using equations in the literature, and good agreement between them is obtained. Consequently, the usefulness of the transducer in measuring the nonlinearity of biological media is successfully demonstrated.

Analysis of acoustic fields from acoustic convex lens

In order to give a wide beam width characteristic to a vibrating element, acoustic convex lenses were fabricated and the diverged acoustic field was investigated experimentally. To design the acoustic lenses, an acoustic field estimation method was proposed by using an angular spectrum method. It was confirmed that the estimation of the diverged acoustic field is possible using the suggested method and the acoustic convex lens can achieve the wide beam width characteristics of the vibrator.

Noninvasive evaluation of spatial distribution of thickness change in myocardium

For the noninvasive diagnosis of heart disease based on movability of the myocardium in the heart wall, the authors have already developed a new method. By the method, velocity signals of the heart wall with small amplitudes less than 10 micrometer on the motion resulting from a heartbeat with large amplitude of 10 mm can be successfully detected with sufficient reproducibility in the frequency range up to several hundred Hertz. The method is applied to multiple points which are set in the heart wall on a ultrasonic beam so that the spatial (depth) distributions of the velocity at these points are obtained. In this paper, from the spatial distributions, the spatial distribution of instantaneous change in thickness is noninvasively evaluated. From in vivo experimental evaluation, clear differences are obtained between healthy subjects and patients with cardiomyopathy, which cannot be obtained by the previously proposed tissue Doppler imaging. This new method offers potential for research on noninvasive acoustical diagnosis of myocardial local movability.