Papers by Author: Yoshiki Yamakoshi

Abstract: An elasticity imaging method using continuous vibration wave excitation is expected to be a safe and quantitative technique. A velocity map is successfully produced by running wave number spectrum analysis of the 2D displacement map of the shear wave propagation. However, a problem is still remained that the accuracy and resolution is not sufficient for medical application. This paper presents an elasticity imaging method based on velocity filtering to clear the boundary of a hard target. We demonstrate an effectiveness of this method through the simulated data.

Abstract: Tissue elasticity measurements by an ultrasonic wave are a promising technique to qualitative diagnosis of tumor or liver diseases. The elasticity in the soft tissue can quantitatively be estimated by velocity of a shear wave propagating through the tissue. For safer and more accurate estimation of the velocity, an elasticity imaging method using continuous vibration wave excitation has been proposed. This method utilizes wave number vector analysis to individually estimate the velocity of the shear waves generated by multiple reflections. In this paper, applicability of the wave number filtering method is discussed to separate the plural shear waves through a phantom experiment. Then, an in-vivo experiment shows possibility to extract anisotropic information of muscle fiber for applying the tissue elasticity measurement.

Abstract: Local shear wave velocity measurements are effective to obtain tissue elasticity map. We have proposed novel wave number spectrum based shear wave velocity measurement system. However, the accuracy and resolution of this technique should be optimized and sophisticated in future clinical application for breast cancer diagnosis. We propose a simulator of RF signal in shear wave velocity measurement system which can consider arbitrary shear wave propagation. We demonstrate the usefulness of this simulator by experimental result. Moreover, accuracy and resolution of small object is discussed for breast cancer application.

Abstract: Quantitative shear wave velocity measurement inside the living tissue is a key technology in future qualitative diagnosis of breast tumor or liver diseases. We develop a novel shear wave velocity measurement system by using running wave number spectrum analysis of the complex displacement of the shear wave propagation excited by a single frequency. The velocity estimation method is demonstrated through the phantom experiments with the developed shear wave displacement measurement system. The validity of the measurement system is demonstrated by comparing with elastic wave simulation results. From the phantom experiments, it is shown that this method has high accuracy of velocity measurement even in the presence of large reflected waves.

Abstract: In order to control a large number of microbubbles with a pumping ultrasonic wave, it is essential to consider a bubble-to-bubble interaction. This paper proposes a simplified microbubble dynamics simulation method considered with bubble-to-bubble interaction in ultrasonic wave field. The microbubble dynamics is solved with difference method based on the Stokes’s low and the secondary Bjerknes force between microbubbles. The laminar flow is considered in the cylindrical calculation region. The effectiveness of the frequency sweep method in laminar flow is shown with simulation results. And a usefulness of this dynamics simulation is also discussed through the experimental result.

Abstract: Generally, a laser Doppler velocimetry can estimate particle velocity by forming a standing wave region with crossed beams and by counting the brinks of particle scattering. If we apply this concept to microwave measurement in near field, an arrayable measurement of object parameters will be expected with low cost. This paper presents a novel velocity and volume estimation method of small object based on reflection coefficient measurement using near field sensor with an interdigital ring coupler structure. The sensor is designed with electrostatic analysis and FDTD analysis. Experiments are carried out with a constructed sensor. Experiments and simulation results agree well. It implies that this sensor has possibility to measure not only the velocity but also the volume of the target.