Tadashi Moriya

Development of a Mechanical Scanning-type Intravascular Ultrasound System Using a Miniature Ultrasound Motor

Intravascular ultrasound (IVUS) plays an important role for the detection of arteriosclerosis, which causes the ischemic heart disease. In mechanical scanning-type IVUS, it is necessary to rotate a transducer or a reflecting mirror. A method that involves rotating the transducer using a torque wire causes image distortion (NURD: non uniform rotation distortion). For a method that involves placing an electromagnetic motor on the tip of an IVUS probe is difficult to miniaturize the probe. Our objectives are to miniaturize the probe (1 mm in diameter, 5 mm in length) and to remove NURD. Therefore, we conducted a study to assess the feasibility of attaining these objectives by constructing a prototype IVUS system, in which an ultrasound motor using a stator in the form of a helical coil (abbreviated as CS–USM: coiled stator–ultrasonic motor) is incorporated, and to clarify problems that need to be solved in constructing the probe.

Imaging System for Intravascular Ultrasonography Using Pulse Compression Technique.

We have developed an imaging system that applies FM-chirp pulse compression technology for use in intraductal ultrasonography, or intravascular ultrasonography. The pulse compression technique attempts to raise resolving power by using average power effectively under peak power restriction. This paper describes a method that use pulse compression technology in intravascular ultrasonography. In this paper, the following are reported: 1) A method to use the FM-chirp pulse compression technique in an imaging system is proposed. 2) A transmission line suited for intravascular ultrasonography is constructed using the L(0, 1) mode of the Pochhmmer-Chree wave propagating in a fused quartz rod coated with carbon. 3) A receiving signal from a target is compressed to give a shot pulse.

A Method for the Measurement of Acoustic Impedance and Speed of Sound in a Small Region of Bone using a Fused Quartz Rod as a Transmission Line

Precise correction for γ-ray attenuation in skull bone has been a significant problem in obtaining quantitative single photon emission computed tomography (SPECT) images. The correction for γ-ray attenuation is approximately proportional to the density and thickness of the bone under investigation. If the acoustic impedance and the speed of sound in bone are measurable using ultrasonic techniques, then the density and thickness of the bone sample can be calculated. Whole bone usually consists of three layers, and each layer has a different ultrasonic character. Thus, the speed of sound must be measured in a small section of each layer in order to determine the overall density of whole bone. It is important to measure the attenuation constant in order to determine the appropriate level for the ultrasonic input signal. We have developed a method for measuring the acoustic impedance, speed of sound, and attenuation constant in a small region of a bone sample using a fused quartz rod as a transmission line. In the present study, we obtained the following results: impedance of compact bone; 5.30(±0.40)×106 kg/(m2s), speed of sound; 3780±250 m/s, and attenuation constant; 2.70±0.50 Np/m. These results were used to obtain the densities of compact bone, spongy bone and bone marrow in a bovine bone sample and as well as the density of pig skull bone, which were found to be 1.40±0.30 g/cm3, 1.19±0.50 g/cm3, 0.90±0.30 g/cm3 and 1.26±0.30 g/cm3, respectively. Using a thin solid transmission line, the proposed method makes it possible to determine the density of a small region of a bone sample. It is expected that the proposed method, which is based on ultrasonic measurement, will be useful for application in brain SPECT.

Inline Transmitter/Receiver System Using Pb(Zn1/3Nb2/3)O3–PbTiO3 Single Crystal and Poly(vinylidene fluoride) for Harmonic Pulse Compression Imaging

An inline transmitter/receiver system for intravascular ultrasound for realizing fine imaging with high resolution and high signal-to-noise ratio (SNR) is newly proposed. This system can be used for tissue harmonic imaging using pulse compression. In this system, a Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN–PT) layer is applied to the transmitter with consideration of efficient transmission, and a poly(vinylidene fluoride) (PVDF) film is used as the receiver because of its wide bandwidth, which is suitable for receiving harmonic components in echo signals. An inline structure, in which the beam axis of a transmitter coincides with that of a receiver, is required to regard the high directivity of the harmonic components as important. In this system, since coded pulses are transmitted from a PZN–PT layer through a PVDF film, which is placed on the transmission side of the PZN–PT layer, a transmitted pulse is mixed with the received echo signal. To avoid such mixing, another PVDF film is placed on the reverse side of the PZN–PT layer to cancel the transmitted pulse. Through experiments, we investigate the effectiveness of the proposed invention, and confirm the feasibility of the proposed system.

A Method to Separate the Transmitting Signal and the Receiving Signal in FM-Chirp Pulse Compression Systems

We have developed a method of separating the transmitting and the receiving signals for FM-chirp pulse compression systems for use in intraductal ultrasonography. The method enables us to remove the unnecessary signals and to obtain a sufficient delay time. In this paper the following results are described: 1) A method to separate the transmitting signal and the receiving signal with a long-time-duration was proposed using a flexible guided line. 2) A guided line suited for intravascular ultrasonography was constructed using the L(0, 3) mode of the Pocchammer-Chree wave propagating in a tapered fused quartz rod. 3) A tentative result was obtained that a transmitting signal of a long-time-duration could be compressed to give a short pulse. 4) To use this guided line in intraductal ultrasonography, a method to design an optimum signal is necessary.

Development of Scanning Method for Puncture Needle-Type Ultrasonography

In this paper, we propose a scanning method for determining the acoustic impedance difference for puncture needle-type ultrasonography using a thin rod. The principle of the proposed scanning method is based on the movements of the end point of a lever. A thin rod is placed on the fulcrum, there by forming a lever. When the end point of the thin rod rotates clockwise forming a circle, the other side of the thin rod moves counterclockwise also forming a circle. By sensing the surface of the sample as a function of the angle made by the thin rod and center axis, scanning can be performed. First, we confirmed that the scanning is possible using the lever; moreover, the movement of the end of the rod is related to that of the other end of the lever. Next, we also confirmed that a one-dimensional image of the amplitude of an interference signal shows the difference in impedance between the polyethylene (PE), acrylic (AC), and polypropylene (PP). The experimental results show that the method is useful for scanning.

Imaging Method for Acoustic Impedance Difference for Puncture Needle-Type Ultrasonography using a Thin Rod with Focusing End Face

In this paper, we propose an imaging method for acoustic impedance difference for puncture needle-type ultrasonography. The difference in acoustic impedance between benign and malignant tissues will provide valuable diagnostic information. In this experiment, a thin rod that has a concave polished end face was constructed using a fused quartz with a diameter of 1 mm and a focus length of 0.3 mm. An ultrasonic wave emitted from the concave end face of the rod is focused on a tissue. The difference in acoustic impedance was determined by the reflection-type interference-based acoustic impedance measurement method. We confirmed that the image shows the difference in impedance between the polyethylene (PE) plate and acrylic rod with a diameter of 3.5 mm embedded therein. The experimental results show that the method is useful for puncture needle-type ultrasonography.

Development of a miniature ultrasonic motor using a helical coil as a stator

Preliminary results for the development of a miniature ultrasonic motor that operates as a traveling wave type ultrasonic motor without the need for a preload spring are presented. The newly developed motor consists of a rotor and a stator that is a helical coil wound inside or outside of the rotor. The coil is constructed using an acoustic waveguide of SUS. An ultrasonic transducer was attached at the end of the waveguide, and the obtained experimental results verify the basic principle of the motor. The torque and revolution speed for a typical motor having a diameter of 2 mm and a length of 5 mm were 60 µN⋅m and 5,000 - 9,000 r.p.m., respectively.

Line clustering with vanishing point and vanishing line

In conventional methods for detecting vanishing points and vanishing lines, the observed feature points are clustered into collections which represent different lines. The multiple lines are then detected and the vanishing points are detected as cross points of those lines. The vanishing line is then detected based on the cross points. However, for the purpose of optimization, these processes should be integrated and achieved simultaneously. In the present paper, we assume that the observed noise for the feature points is a two-dimensional Gaussian noise. And we define the likelihood function including obviously vanishing point and vanishing line parameters based on a Gaussian mixture density model. As a result the described simultaneous detection can be formulated as a maximum likelihood estimation problem. In addition, an iterative computation method for achieving this estimation is proposed based on the EM algorithm. The proposed method involves new techniques by which stable convergence is achieved and the computational cost is reduced. The effectiveness of the proposed method including these techniques can be confirmed by some experiments.

The effect of filler particle size on ultrasonic image of electrical breakdown region in filler-added insulating materials

The ultrasonic visualization method proposed provides an effective way to detect or visualize the electrical breakdown region in specimens of organic insulating materials even when filled with powder materials. However, there exist a few problems on ultrasonic visualization for such kinds of resins, mainly due to their peculiar acoustic characteristics, i.e. specific acoustic impedance, heavy signal decay within the material and scattering noises from filler particles. Above all, scattering noises prevent the formation of clear ultrasonic images of the electrical breakdown region. In this paper we report the dependence of filler particle size on the magnitudes of scattering noises reflected from filler particles, and recommend the use of filler materials with smaller particle size for convenient future insulation diagnosis.