Hiroki Takahashi

Echo speckle imaging of blood particles with high-frame-rate echocardiography

Cardiac blood flow patterns such as the vortex flow pattern inside the left ventricle have been studied to provide new information for the diagnosis of the pumping function of the human heart. Complex blood flow is visualized by imaging echo speckles of blood particles because the speckle-like texture translates to the motion of blood particles. We proposed an imaging method for echo speckles of blood particles using high-frame-rate ultrasound for the visualization of the intracardiac blood flow direction. High-frame-rate ultrasound is useful for continuously observing the fast motion of echoes from blood particles in the heart. In the present study, weighting by coherence and compounding the magnitudes of echo signals in different transmissions were introduced to visualize weak echoes from blood particles. The feasibility of the visualization of cardiac blood flow using high-frame-rate ultrasound was demonstrated by basic and in vivo experiments.

Na3Ca2TaO6, a rock-salt superstructure phase with a fully ordered cation arrangement

The title quaternary oxide, trisodium dicalcium tantalum hexaoxide, is isostructural with Li(3)Ni(2)TaO(6), a partially ordered rock-salt phase. The Na, Ca and Ta atoms occupy octahedral sites in an orderly manner and form a cation-ordered superstructure.

Echo motion imaging with adaptive clutter filter for assessment of cardiac blood flow

Visualization of the vortex blood flow in the cardiac chamber is a potential diagnostic tool for the evaluation of cardiac function. In the present study, a method for automatic selection of the desirable cutoff frequency of a moving target indicator filter, namely, a clutter filter, was proposed in order to visualize complex blood flows by the ultrahigh-frame-rate imaging of echoes from blood particles while suppressing clutter echoes. In this method, the cutoff frequency was adaptively changed as a function of the velocity of the heart wall (clutter source) in each frame. The feasibility of the proposed method was examined through the measurement of a healthy volunteer using parallel receive beamforming with a single transmission of a non-steered diverging beam. Using the moving target indicator filter as above with the cutoff frequency determined by the proposed method, the vortex-like blood flow in the cardiac chamber was visualized as movements of echoes from blood particles at a very high frame rate of 6024Hz while suppressing clutter echoes.

Intraventricular blood flow vector and streamline imaging using high frame rate cardiac ultrasound

The relationship between the complex blood flow inside the human heart and the cardiac pumping function has received attention in recent years. We previously proposed a method for high-frame-rate imaging of echoes from blood particles with diverging beam transmission in order to visualize the flow direction in the human heart. In the present study, the velocity vector estimator with speckle-tracking technique using the inter-frame movement of blood echoes acquired at a very high-frame-rate was evaluated. Furthermore, the visualization of streamline was demonstrated by the 4th-order Runge-Kutta method with the obtained blood velocity vector. The accuracy of velocity vector estimation by the speckle-tracking technique suffers from low signal-to-noise ratios of echoes from tiny echo sources (blood particles) and low acoustic output of diverging beam. Hence, in this study, two-dimensional correlation functions used for the speckle-tracking technique were temporally averaged for a stable estimation of velocity vectors. In the steady flow experiment, it was confirmed that the estimation accuracy was improved by averaging of correlation functions even during 2 ms. The echo data was acquired in in vivo measurement of a 27-year-old healthy male at the ultrahigh-frame-rate of 6250 Hz with the single transmission of a non-steered diverging beam per frame. The fluxes flowing into and out of the cardiac cavity were visualized by blood flow vectors estimated by the speckle-tracking technique with averaging of correlation functions. In mid diastole, the vortex-like flow appeared in the distribution of velocity vectors. The blood flow toward the apex side of the heart was visualized by the obtained streamline in rapid filling phase.

Na2Ca3Ta2O9 with a simple stacking of oxygen triangular nets

The crystal structure of the title quaternary oxide, disodium tricalcium ditantalum nonaoxide, has a distorted simple hexagonal packing of the O atoms. The Na, Ca and Ta atoms are positioned in oxygen trigonal prisms. Two oxygen prisms containing Ta atoms constitute face-sharing prisms of [Ta 2 O 9 ] 8- .

Speckle-enhanced cardiac blood flow imaging with high frame rate ultrasound

Blood flow imaging in echocardiography helps users to evaluate the pumping function of the human heart. As a typical method, color Doppler imaging has been widely used to obtain the information of intracardiac blood flow. Color Doppler imaging, however, does not show the direction of blood flow stream because only flow velocity along a scan line is estimated. Echocardiographic particle image velocimetry (E-PIV) technique gives flow characteristic information, such as velocity vector fields and stream lines of blood flow, which are calculated based on motions of ultrasonic echoes from contrast agent. However, E-PIV is an invasive approach forcing physical and mental burden on patients because of intravenous injection of a contrast agent. To overcome this problem, we propose a non-invasive method for cardiac blood flow imaging by visualization of motions of echoes from blood particles. High frame rate measurement by parallel receive beamforming with spherically diverging wave was used for continuous observation of echoes from the same blood particles between frames. In addition, a coded excitation with 5-bit Barker code and clutter filtering were also used to enhance weak echoes from blood particles. Moreover, the power of echo signal was weighted by coherence calculated from demodulated signals to suppress the random noise which remained after clutter filtering. Through in vivo measurement of a 26-year-old healthy male, B mode image overlaid with enhanced echo speckle of blood particle was obtained in the three chamber view. Moreover, velocity vectors of blood flow could be estimated by applying enhanced echoes of blood particles with speckle tracking technique. The estimated velocity vector showed that blood is flowed out to the aorta in systole and is flowed into the left ventricular cavity in diastole. The in vivo result shows a potential of non-invasive imaging of blood flow pattern at high temporal and spatial resolution using our proposed method.

Automated Identification of the Heart Wall Throughout the Entire Cardiac Cycle Using Optimal Cardiac Phase for Extracted Features

In most methods for evaluation of cardiac function based on echocardiography, the heart wall is currently identified manually by an operator. However, this task is very time-consuming and suffers from inter- and intraobserver variability. The present paper proposes a method that uses multiple features of ultrasonic echo signals for automated identification of the heart wall region throughout an entire cardiac cycle. In addition, the optimal cardiac phase to select a frame of interest, i.e., the frame for the initiation of tracking, was determined. The heart wall region at the frame of interest in this cardiac phase was identified by the expectation?maximization (EM) algorithm, and heart wall regions in the following frames were identified by tracking each point classified in the initial frame as the heart wall region using the phased tracking method. The results for two subjects indicate the feasibility of the proposed method in the longitudinal axis view of the heart.

Improvement of Automated Identification of the Heart Wall in Echocardiography by Suppressing Clutter Component

For the facilitation of analysis and elimination of the operator dependence in estimating the myocardial function in echocardiography, we have previously developed a method for automated identification of the heart wall. However, there are misclassified regions because the magnitude-squared coherence (MSC) function of echo signals, which is one of the features in the previous method, is sensitively affected by the clutter components such as multiple reflection and off-axis echo from external tissue or the nearby myocardium. The objective of the present study is to improve the performance of automated identification of the heart wall. For this purpose, we proposed a method to suppress the effect of the clutter components on the MSC of echo signals by applying an adaptive moving target indicator (MTI) filter to echo signals. In vivo experimental results showed that the misclassified regions were significantly reduced using our proposed method in the longitudinal axis view of the heart.

Swarm of micro-quadrocopters for consensus-based sound source localization

Graphical Abstract Abstract In this paper, we propose an algorithm for simultaneous indoor self-localization and Sound Source Localization (SSL) using a swarm of microphone-embedded-micro-quadrocopters (size 10 cm). Micro-quadrocopters are extremely noisy, have low CPU power and cannot lift heavy equipment: the small payload of each micro-quadrocopter (5 g) only allows us to equip it with one microphone in addition to the inbuilt motion sensors. To perform robust SSL despite these issues, we propose three functions: (1) Self-localization of the quadrocopters using sound landmarks placed in the environment, and simultaneous localization of unknown sound sources; (2) Sound source detection; (3) Distributed data fusion based on noisy information from all members of the swarm. To achieve these, we propose three algorithms that are robust to noise, can perform with a varying number of quadrocopters, and do not rely on GPS nor motion capture to allow indoor operations: (1) A sound-based Unscented Kalman Filter (UKF) for self-localization of each quadrocopter; (2) A peak-based algorithm for sound source detection; (3) A distributed SSL algorithm for swarms with consensus-based integration using a new filter termed Unscented Kalman Consensus Filter (UKCF). We evaluated the proposed methods in real world and in simulated environments. The preliminary results show that the sound-based UKF represents an improvement of 37% on position estimation precision compared to basic dead reckoning approaches, even when the theoretical assumptions are violated; the distributed UKCF gives an improvement of 85% on SSL compared to a single-sensor approach in simulation.

Two dimensional blood velocity estimation using high frame rate echocardiography with transverse oscillation approach

Blood velocity estimation in the cardiac cavity has been useful to diagnose the heart function. In recent years, the two-dimensional (2D) blood velocity has been estimated by detecting echoes from blood cells obtained by high-frame-rate echocardiography with diverging ultrasound emission and parallel receive beamforming. However, the stability of estimated velocities in the transverse direction (perpendicular to the axial direction) was not enough due to a low transverse frequency of an echo. The transverse frequency can be increased by the receive apodization used in the transverse oscillation (TO) approach. In the present study, the effect of the TO apodization on the accuracy of the blood velocity estimation was examined and the receive apodization was optimized. The errors in 2D velocity vectors estimated by speckle tracking were evaluated by an in-house simulation software which simulates echoes from a scatter-filled tube. The movements of the scatterers were governed by the Hagen-Poiseuille flow with a velocity of 0.4 m/s. In the obtained result, the standard deviations of estimated transverse velocities were 9.5% with the rectangular apodization, 17.0% with the Hanning apodization, and 17.5% with the TO apodization with a distance between peaks in the apodization of 48 elements, respectively, at a flow angle of 45 degree.