Norio Tagawa

Performances of Various Types of Constrained Interpolation Profile Method for Two-Dimensional Numerical Acoustic Simulation

To date, various types of constrained interpolation profile (CIP) analysis have been proposed. In this study, the authors first examined the calculation accuracy of two-dimensional (2-D) acoustic field analysis by the CIP-conservative semi-Lagrangian of the second-order (CIP-CSL2) method, in which values of the acoustic field and the integrals between two neighboring points are used, whereas the CIP method involves the use of the values of the acoustic field and their derivatives at grid points. The results obtained by the CIP-CSL2 method, type-M CIP method, and type-C CIP method were compared for a 2-D acoustic field. The results indicate that CIP-CSL2 analysis provides high accuracy of the same order as that of the type-C CIP method. We also investigated the run-time and memory required for this method.

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.

Two-Dimensional Simulation of Nonlinear Acoustic Wave Propagation Using Constrained Interpolation Profile Method

In this study, a numerical simulation of the nonlinear sound wave propagation in the time domain is demonstrated by constrained interpolation profile/cubic-interpolated pseudoparticle (CIP) method. The CIP method is a novel numerical scheme which was proposed by Yabe et al. It is a method of characteristics (MOC) and is a low-dispersion and stable scheme. The CIP method is suitable for analysis of nonlinear wave propagation including weak shock formation because the rapid pressure change, such as that caused by a shock front, easily causes numerical dispersion error in a conventional numerical scheme. Some of the authors have reported application of the CIP method to a one-dimensional nonlinear sound wave propagation in air. Then, we demonstrate a numerical calculation of the nonlinear sound wave propagation for a two-dimensional acoustic field.

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.

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.

Examination of Sub-Grid Technique for Simulation of Sound Wave Propagation Using Constrained Interpolation Profile Method with Method of Characteristics

The constrained interpolation profile (CIP) method is a novel low-dispersive numerical scheme. It is a kind of method of characteristics (MOC). In our past study, we applied the CIP method to numerical analyses of sound wave propagation. For simulations of complicated heterogeneous media or large-scale simulations of wave propagation, a new grid system is indispensable. In this study, we examined a sub-grid technique for the CIP acoustic wave simulation. It is clarified that this technique has the advantages of its small memory requirements and less calculation time.

Medical Ultrasound Imaging Using Pulse Compression Technique Based on Split and Merge Strategy

A medical ultrasound image with a high spatial resolution and a high signal-to-noise ratio (SNR) is required for precise diagnosis. However, when a long chirp pulse is transmitted in order to improve the SNR, both the transmitted signal and the echo signal overlap. The dynamic range of the analog-to-digital (A/D) converter should be adjusted to that of the echo signal, and the transmitted pulse is saturated. Therefore, the transmitted pulse cannot be compressed completely, and the echo signal cannot be extracted from the overlapped signal. This indicates that a long chirp signal makes near-field imaging impossible. In this paper, we propose a method that can realize near- and far-field imaging processes with higher SNRs. The proposed method is based on a split-and-merge strategy. As a result, it is shown that our proposed method gives both near- and far-field images with approximately 40 dB higher SNRs than the short pulse.

Examination on Fast Algorithms of Compact Finite Difference Calculation for Finite Difference Time Domain Acoustic Wave Simulation

In this study we examined a fast and efficient calculation method for compact finite-differences (FDs). The proposed method employs a recursive filter (RF) method. This method is based on z-transformation and its RF algorithm. Analysis of sound propagation using compact FDs with the RF method was implemented. Using the RF algorithm, we can implement compact finite difference time domain (FD-TD) analysis as a simpler code than a conventional technique using LU factorization, i.e., the Tomas method. The results obtained in this study clarified that the RF method reduces calculation time required for compact FDs.

High Signal-to-Noise Ratio Ultrasonic Point Detection Method using a Fused Quartz Rod as a Pulse Compression Filter and a Sensor

In this paper we propose a method to detect ultrasound with high signal-to-noise ratio (S/N) at a point on the surface of a material. To obtain high S/N, we applied an frequency-modulation (FM) pulse compression method as used in radar. We also used a fused quartz rod for point detection, at the same time using it for the pulse compression filter. The concept is demonstrated with an image reconstructed using a computer tomography algorithm.