Hirotaka Yanagida

A reaction kinetics model of water sonolysis in the presence of a spin-trap

The time development of the concentration of a spin-trapped OH radical was studied by electron spin resonance at various sound intensities and various 5,5-dimethyl-1-pyrroline N-oxide (DMPO) concentrations in water sonolysis. The lifetime of the spin-trapped OH radical was also studied, and factors governing sonolysis are discussed. We found that the production of spin-trapped OH radical increases with increasing ultrasound intensity. The lifetime of a spin-trapped OH radical decreases linearly with increase in sonication time. This result suggests that an unknown scavenger is produced by ultrasound. Based on the above results, we suggested a model of the reaction kinetics and estimated the production rate of OH radical from this model.

Chaotic mixing generated by acoustic streaming

The acoustic mixer presented in this paper is a closed cylinder containing chemical solutions. The ultrasound was generated in a water bath outside of the cylinder. The mixing efficiency was measured by using a laser-photodiode system and by mixing iodine and sodium thiosulfate. Iodine solution has a light brown color which becomes transparent if the solution is mixed with sodium thiosulfate. The unmixed regions of the solution in the container remain dark. Starch was used to make the solution darker. Considering the relative position between the cylinder and the transducer, it was shown that displacements parallel to the axes of the streaming have little effect on the mixing speed. Indeed, the distance of the cylinder from the center of the streaming is more important to obtain ideal mixing performances. The frequency and size of the transducers has been investigated too and little effect was found. In contrast, the wave amplitude seems to be the biggest factor in obtaining rapid mixing.

Development of ultrasonic time-of-flight computed tomography for hard wood with anisotropic acoustic property

The ultrasound computed tomography (CT) method presented in this paper is an improvement of conventional back projection imaging methods for wooden pillars. The sound velocity in wood changes with the direction of the ultrasound propagation path; therefore, the properties of a medium must be considered in the imaging method. We obtained the 36 time-of-flight (TOF) data of tangents on the same circumference for various diameters. We determined an irregular pathway for each diameter, if the sound velocity of the pathway is slower than 92% of the average velocity of 36 pathways. TOF data for 270 paths were measured in total by manual scanning for one CT image. Although a hole of 25 mm diameter and a slit-type (3×33 mm2) hole are not detected by the conventional back projection method, these artificial defects were detected by our method. Two slit-shaped defects were also detected by our method. We found some knots and cracks in the X-ray image in a wood specimen. These knots were detected by our method; however, it was impossible to distinguish the knots and holes from each other using the CT image.

Effect of Ultrasound Frequency on Sonochemical Luminescence under Well-Determined Sound Pressure

By determining sound pressure using the Ramann-Nath parameter and confirming sound form based on schlieren images, we investigated the effects of ultrasound frequency on the sonochemical luminescence of a luminol solution. Separating the effect into the luminescence threshold of sound energy and the rate of luminescence increase with respect to the sound energy, we found that the lower the frequency is the lower the threshold and the higher the rate of increase, and that only the standing-wave induces luminescence under the conditions where the running-wave does not induce luminescence at all.

Observation of Dynamic Structure Using Ultrasound 3D Imaging System with Encoded Wave Front

Dynamic ultrasound three-dimensional (3D) imaging using coded transmission is described. A sequence of 3D images of moving objects is reconstructed for each transmission of pulses modulated by Walsh functions. Then, the dynamic structure of the objects is extracted from the image sequence. In this paper, we discuss the relationship of the system performance to the parameters of the transmitting code such as duration time, repetition period, and total transmission length. A Doppler shift estimation and motion compensated image reconstruction method is described. The computer simulation for the motion compensation image reconstruction was carried out. Ultrasound 3D stroboscopic photography was demonstrated by a preliminary experiment utilizing the evaluation system in a 3D medical diagnostic scanner which has 32 transmitters and 32 receivers.

High-speed 3D imaging system using coded wavefront generated by Walsh function modulated signals

An experimental ultrasonic three dimensional (3D) imaging system for high-speed data acquisition has been developed. A 3D image can be reconstructed for each transmission of pulses modulated by Walsh functions. Matrix transducers of 40/spl times/40 2 MHz elements and a data acquisition system have been developed to evaluate the system performance. In this paper, we describe the principle, the fabrication process of the 2D array, and the data acquisition system. Three dimensional images of 20 dB dynamic ranges were successfully obtained for standard ultrasonic phantoms with 32 transmissions using the developed system.

Image Quality Improvement of Ultrasonic Computed Tomography on the Basis of Maximum Likelihood Expectation Maximization Algorithm Considering Anisotropic Acoustic Property and Time-of-Flight Interpolation

The anisotropic acoustic property is considered for the purpose of improving the image quality of the ultrasonic computed tomography (CT) scans of a wooden pillar. We propose a velocity anisotropy correction method of time-of-flight (TOF) data for image reconstruction on the basis of the maximum likelihood-expectation maximization (ML-EM) method. We also examine the effect of the interpolation of the TOF data as the density of the TOF data has a considerable effect on image quality in the ML-EM method. The feasibility of velocity anisotropy correction and TOF data interpolation are examined in detail using numerical and wood phantoms.

Motion Detection in Ultrasound Image-Sequences Using Tensor Voting

Motion detection in ultrasound image sequence using tensor voting is described. The system adopts synthetic aperture focusing techniques and short duration coded signals to realize high-speed data acquisition. However, many artifacts appear in the reconstructed image sequence because of the incompleteness of the transmitted code and insufficient number of array elements. In this paper, we examined the application of the tensor voting for precise motion detection and artifact reduction in synthetic aperture focusing technique.

P2B-6 Parallel Image Reconstruction Operation by Dedicated Hardware for Three-Dimensional Ultrasound Imaging

The feasibility of three-dimensional (3D) ultrasound imaging methods involving computations depends on the performance of a computer. To realize efficient high-speed image reconstruction, we examined hardware (HW) implementation that is required. The HW was designed by using VHDL for implementation on a field-programmable gate array (FPGA). This paper first presents an image reconstruction algorithm and subsequently discusses the dedicated HW architecture for performing the image reconstruction.

Two-Dimensional Pb(ZrxTi1-x)O3 Ceramics Arrays for a High-Speed Three-Dimensional Imaging System Using a Coded Wavefront

A two-dimensional matrix Pb(ZrxTi1-x)O3 (PZT) ceramics array has been developed to evaluate the principle of an imaging system using a coded wavefront. In this paper, the fabrication process of a PZT 40 ×40 element array for transmitter and receiver is described. Signals modulated by the Walsh functions were used for driving the transmitter array elements. Three-dimensional images were successfully obtained for a standard ultrasonic phantom. It is shown that this method is applicable in medical diagnosis.